188

FAILURE TERMS an excerpt from SSPC's Protective Coatings Glossary

A

ABRASIONThe wearing away of a surface by action such as by rubbing, scraping, erosion, or otherfrictional process.

ABRASION RESISTANCEThe ability of a coating to resist being worn away and to maintain its original appearanceand structure when subjected to rubbing, scraping and wear. [ASTM]

ACCELERATED AGINGAny set of conditions used in an attempt to produce in a short time the results obtainedunder normal conditions of aging. In accelerated aging tests, the usual factors considered areheat, light, water, and oxygen, either separately or combined. [Painting/Coatings Dictionary]

ADHESION FAILUREA failure between two distinct coating layers or between the substrate and the first layer ofcoating. See ADHESION TEST, TENSILE (PULL-OFF) in main glossary.

ADULTERATIONThe addition of foreign materials to a manufactured product.

AFTER-TACKFilm defect in which the coated surface, having once reached a tack-free state, subsequentlydevelops a sticky condition. [CED]

AGING(1) Storage of paints, varnishes, etc., under defined conditions of temperature, relative hu-midity, etc., in suitable containers, or as dry films of these materials for the purpose of sub-sequent tests [Painting/Coatings Dictionary]; (2) Gradual changing of a coating’s chemicaland/or physical properties over a period of in-service response time.

AIR BUBBLEDry bubble in coating film caused by entrapped air. [CED]

AIR ENTRAINMENT(1) The process of causing small air bubbles to form in paint or wet paint film; (2) Intentionalincorporation of small air bubbles in concrete to improve such physical properties as freeze-thaw resistance.

AIR ENTRAPMENTInclusion of air bubbles in coating film or other solids such as concrete. [CED] See BUB-BLING.

ALLIGATORING(1) A type of crazing or surface cracking of a definite pattern, as indicated by its name. Theeffect is often caused during weather aging; (2) the cracking of the surface bitumen on abuilt-up roof, producing a pattern of cracks similar to an alligator’s hide; the cracks may notextend through the surface bitumen. [CED]; surface cracking of a paint film having the ap-pearance similar to alligator hide. [ASTM]; alligator cracking is the vertical cracking of acoating with a pattern of closed cells or islands of unbroken coating. See also CRACKING.

AMINE BLUSHSurface opalescence (blush) on epoxy films caused by reaction of amine co-reactant with car-bon dioxide and water to form an amine carbamate. This can affect adhesion of any subse-quent coat if not properly removed.

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FAILURE TERMS

ANTI-FOAMING AGENTAdditive used to control or prevent foam formation during the manufacture or application ofcoatings.

ANTI-LIVERING AGENTAdditive used to prevent the livering of a coating. See LIVERING.

ANTI-SAG AGENTAdditive used to control sagging of a coating.

ANTI-SETTLING AGENTSubstance incorporated into a pigmented paint to retard settling and to maintain uniformconsistency during storage or painting operations. These additives normally function by al-tering the rheological properties of the paint.

ANTI-SKINNING AGENTAny material added to a coating to prevent or retard the processes of oxidation or polymer-ization that result in the formation of an insoluble skin on the surface of the coating in acontainer. [Painting/Coatings Dictionary]

ANTI-WRINKLING AGENTMaterial added to surface coating compositions to prevent the formation of wrinkles in filmsduring curing.

B

BALD SPOTArea or patch, usually in a wrinkle finish film, which has failed to wrinkle or give the desiredoptical effect. [CED]

BIOCIDEA chemical agent capable of killing organisms such as those responsible for microbiologicaldegradation.

BIODETERIORATIONAny undesirable change in material properties brought about by the activities of microor-ganisms. [CED]

BIOFOULINGBiological encrustation of surfaces in sea water by flora and fauna, e.g., barnacles. See FOUL-ING.

BIOLOGICAL DEFACEMENTDisfiguring of surfaces by growth of microorganisms.

BLEACHING(1)Bleaching is a uniform loss of color of a paint or varnish. This may be due to internalchemical or physical action in the paint itself, to influences from the surface on which it isapplied or to weathering or contamination from the atmosphere; (2) Intentional lightening ofthe color of a material such as wood, vegetable oils, varnishes, etc. [CED]; removing color.[AM]

BLEEDCoating discoloration by the diffusion of coloring matter from a previously painted or un-painted surface (e.g. asphalt) by the action of the coating solvent.

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FAILURE TERMS

BLEEDINGThe diffusion of colored matter from a substrate (including a previously applied paint film)into a newly applied finish, resulting in a discoloration of the finish. The solvent carrier ofthe newly applied finish normally transfers the coloring matter. Examples are bituminoussurfaces, wood knots, organic pigments, contaminants.

BLEEDING KNOTUsually circular-shaped discoloration in stained or painted siding. [CED]

BLEED-THROUGHAppearance of color on a newly painted surface by migration of a previously painted sub-strate beneath it.

BLISTERAn undesirable rounded elevation of the coating resulting from the local loss of adhesion.See also BLISTERING.

BLISTERING(1) Formation of dome-shaped projections (blisters) in paints or varnish films resulting fromlocal loss of adhesion and lifting of the film from an underlying paint film (intercoat blister-ing) or the base substrate. The standard test method for evaluating the degree of blisteringof paints is described in ASTM D 714; (2) The irregular raising of a thin layer at the surfaceof placed mortar or concrete during or soon after completion of the finishing operation, or inthe case of pipe after spinning; also bulging of the finish plaster coat as it separates anddraws away from the base coat [ACI]; (3) Formation of blisters in films of paint or varnish.Blistering may be caused by solvent entrapment, moisture diffusion through the coating, orexcessive moisture in the substrate.

BLISTERING RESISTANCEA coating’s ability to resist the formation of blisters.

BLOCK COATA barrier coat or transition primer/tie coat that prevents incompatible paints from touching.See also BARRIER COAT, TIE COAT in main glossary.

BLOCKING(1) The undesirable sticking together of two painted surfaces when pressed together undernormal conditions or under specified conditions of temperature, pressure, and relative hu-midity; (2) Undesired adhesion between touching layers of material, such as occurs undermoderate pressure and sometimes pressure and heat, during storage or fabrication. [CED]

BLOCKING RESISTANCEThe ability of two coated surfaces to resist sticking together during normal handling andstorage.

BLOOMINGThe reduction of a coating gloss caused by materials exuding in or from an applied film.Unlike bleeding, the solvent-caused movement of material is from the coating itself and notthe substrate.

BODYINGThickening of an oil through thermal processing; (2) An increase in the viscosity or thixot-ropy of a paint, varnish, or lacquer which occurs during storage. [MPDA]

BOUNCE BACK(1) The rebound of atomized paint particles during spray application. This effect is mostpronounced when paint is being applied into corners or boxed areas. The resultant returnflow of atomized air carries some of the paint particles away from the surface. See also DRYSPRAY, OVERSPRAY; (2) Rebound of abrasive particles during abrasive blasting.

191

FAILURE TERMS

BRITTLESusceptible and being easily broken, fragile.

BRITTLENESSDegree of susceptibility to cracking or breaking by bending. [AM]

BRONZINGA subjective, descriptive, appearance term applied to metal-like reflectance which sometimesappears at the surface of nonmetallic colored materials. It is perceived at the specular angle,by observing the image of a white light source, for example, and is characterized by a distincthue of different predominant wavelength than the hue of the paint itself. The origin of theselective specular reflectance is generally considered to be reflectance from very small par-ticle size pigments partially separated from the surrounding vehicle at or near the surface.[CED]

BRUSH MARKS(1) Marks produced in a coating by the bristles of a brush during application. Depending onthe leveling characteristics of the paint, brush marks may or may not remain in the driedcoating; (2) Small ridges or valleys produced in a paint film by the combing action of thebristle of a brush. [CED]

BUBBLE BUSTERCompound used to control the formation of bubbles in a coating.

BUBBLINGAir bubbles or solvent vapor bubbles found temporarily in the wet film of a coating or perma-nently in the dry film.

BUG HOLESSmall regular or irregular cavities, usually not exceeding 15 mm in diameter, resulting fromentrapment of air bubbles in the surface of formed concrete during placement and compac-tion.

C

CAKINGHard setting of pigment from a liquid paint during storage.

CAN STABILITYResistance to deterioration of liquid paint in original container.

CASE HARDENINGSurface hardening without thorough drying of film.[CED] See SURFACE DRYING, TOPDRYING in main glossary.

CATASTROPHIC COATING FAILUREA coating failure that is sudden, very dramatic, and serious.

CATASTROPHIC CORROSIONMetallic degradation resulting in substantial loss of metal.

CAT EYE(S)Hole or holiday shaped like a cat’s eye; cratering. [AM] See CRATERING.

CATHODIC DISBONDINGMechanical lifting of a coating caused by hydrogen bubbles formed when cathodic protection

192

FAILURE TERMS

is excessive.

CAVITATIONThe formation and instantaneous collapse of innumerable tiny voids or cavities within aliquid subjected to rapid and intense pressure changes. Cavitation produced by ultrasonicradiation is sometimes used to effect violent localized agitation. Cavitation caused by severeturbulent flow often leads to cavitation damage. [ASM]

CAVITATION CORROSIONA process involving conjoint corrosion and cavitation. [ASM]

CAVITATION EROSIONProgressive loss of original material from a solid surface due to continuing exposure to cavi-tation.

CHALKINGThe formation of loose powder on the surface of a coating, usually caused by degradation ofthe organic binder by the sun’s ultraviolet light. ASTM D 4214 is the Standard Test Methodfor Evaluating the Degree of Chalking of Exterior Paint Films.

CHALKING RESISTANCEThe ability of a pigmented coating to resist chalking. See also CHALKING.

CHAMPAGNE FINISH (EFFERVESCENCE)The slight surface roughening caused by small bubbles of escaping solvent vapor.

CHECK(S)Fine, shallow cracks in a coating resulting from surface weathering.

CHECKING(1) The fine cracking that develops in paint films during prolonged curing and/or weatheringthat does not penetrate to the underlying surface. ASTM D 660 is a Standard Test Method forEvaluating Degree of Checking of Exterior Paints; (2) Development of shallow cracks at closelyspaced but irregular intervals on the surface of plaster, cement paste, or concrete [ACI].

CHECKING RESISTANCEThe ability of a coating to resist checking. See also CHECKING, CRACKING RESISTANCE.

CHIPPINGTotal or partial removal of a dried paint film in flakes by accidental damage or wear duringservice; in traffic paints, this failure is usually characterized by sharp edges and definitedemarcation of the base area. [CED]. ASTM D 913 is the Standard Test Method for Evaluat-ing Degree of Resistance of Wear to Traffic Paint. ASTM D 3170 is the Standard Test Methodfor Chipping Resistance of Coatings.

CHIPPING RESISTANCEThe ability of a coating or layers of coatings to resist total or partial removal, usually insmall pieces, resulting from impact by hard objects or from wear during service.

CISSINGA mild form of crawling.

CLOUDINESSThe lack of clarity or transparency in a paint or varnish film. [CED]

COATING FAILURELoss of a coating’s function or purpose, i.e., when it no longer protects the substrate, provides

193

FAILURE TERMS

an attractive appearance, or serves some other function such as providing a non-slip surface.The time of failure is considered to occur when some action is needed to restore its propertiesto the level necessary to again provide its intended purpose.

COBWEBBINGThe rapid drying of a coating (often a lacquer) during application to form fine strings insteadof normal atomization.

COHESIONThe propensity of a substance to adhere to itself. The force holding a substance together.[Painting/Coatings Dictionary] The ability of a single coating layer to resist internal parti-tioning or fracturing.

COHESIVE FAILUREA failure or break within a given coat or material (the coating breaks within itself).

COLD CHECKINGThe formation of hairline cracks in lacquers exposed to low temperatures.

COLD CRACKINGCrazing and cracking of a coating subjected to low temperatures or cold/ambient cycling.[CED]

COLD WALL EFFECTIn tank linings, a driving, permeating force assisting ionic passage through a coating to ametal in the direction from a hot liquid to a cold wall.

COLORFASTNESSThe ability of a film of paint or varnish to show little change in original color after beingexposed to a specific environment, generally light and weathering.

COLOR RETENTIONProperty of a material relating to its ability to maintain constant color during surface expo-sure, especially to sunlight. Color retention requirements usually are described in terms ofcolor difference defined according to a standard test procedure.

CONTAMINATIONCondition causing a surface, material, or process to become dirty or impure; also, the mate-rial that causes a surface to be in this state.

CORROSIONThe chemical or electrochemical reaction between a metal and its environment that resultsin the loss of material and its properties. Metals corrode because they exist in chemicallyunstable states.

CORROSION FATIGUEThe process in which a metal fractures prematurely under conditions of simultaneous corro-sion and repeated cyclic loading at lower stress levels or fewer cycles than would be requiredin the absence of the corrosive environment.

CRACKING(1) The splitting of a dry paint film. Different types of cracking include hair-cracking orhairlines, checking, cracking, crazing, crocodiling or alligatoring, and mud cracking. Thestandard test method for evaluating degree of cracking is described in ASTM D 661; (2) Tobreak up into simpler chemical components, as with cracking of petroleum.

CRACKING RESISTANCEThe ability to resist formation of cracks that extend through at least one coat of paint. See

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FAILURE TERMS

CRACKING, CHECKING RESISTANCE.

CRACKLETopcoat cracking caused by application of topcoat before the previously applied coat has suf-ficiently cured.

CRATERINGThe formation of small, shallow depressions in a coating generally resulting from foreignmatter in or deposited on the wet film.

CRATERSSmall, rounded depressions in a coating film that do not expose the previous coat or thesubstrate. See CRATERING.

CRAWLINGThe drawing back of a liquid film from a uniformly thick layer to form areas of little, if any,thickness. It occurs when the surface tension of the coating is greater than the surface ten-sion of the substrate. [WJP]

CRAZINGA network of intersecting checks or cracks appearing on a coated surface. See CRACKING.

CREEPAGESee CRAWLING, UNDERCUTTING.

CREVICE CORROSIONCorrosion that occurs within or adjacent to a crevice formed by contact with two pieces of thesame metal or another metal or with a nonmetallic material. In these locations, the inten-sity of attack is usually more severe than on surrounding areas of the same metal surface.[Painting/Coatings Dictionary]

CRINKLINGSee WRINKLING.

CROCKINGRemoval of color upon abrasion or rubbing. Staining of a white cloth by rubbing lightly overa colored surface. [Painting/Coatings Dictionary]

CROCKING RESISTANCEThe ability of a coating to resist color transfer when rubbed or abraded.

CROCODILINGSee ALLIGATORING.

CROWS FOOTINGA coating film defect in which a pattern of wrinkles resembling a crow’s foot is formed. SeeWRINKLING.

CURTAININGSee SAGGING.

CURTAINSSags with a draped appearance.

D

DEFECTA surface or film imperfection (flaw), deficiency, or incompleteness that deviates from a speci-

195

FAILURE TERMS

fication or industry-accepted condition.

DEFLOCCULANTAn additive that prevents pigments in suspension from coalescing to form flocs.

DEFOAMER(S)Additives used to reduce or eliminate foam formed in a coating or coating constituent. SeeANTI-FOAMING AGENT.

DEGRADATIONA gradual loss of coating materials and/or properties resulting from their service conditionsand weathering.

DELAMINATESee DELAMINATION.

DELAMINATION(1) The separation of a coat or coats of paint from the previous coat or from the substrate.Failure of a coating to adhere to the previous coating; (2) In the case of a concrete slab, ahorizontal splitting, cracking, or separation of a slab in a plane roughly parallel to, andgenerally near, the upper surface; found most frequently in bridge decks and caused by thecorrosion of reinforcing steel or freezing and thawing; similar to spalling, scaling, or peelingexcept that the delamination affects large areas and can often be detected by tapping. [ACI]

DETACHMENTSee DISBONDING.

DETERIORATIONSee DEGRADATION.

DEZINCIFICATIONSelective loss of zinc metal from a brass alloy.

DILATANCYStiffening and loss of fluidity of paint upon agitation. The opposite of thixotropy.

DIRT ACCUMULATIONThe collection of air-borne dirt, soot, or other foreign material on the exterior surfaces ofcoatings or other substrates. ASTM D 3274 is the standard Test Method for Evaluating De-gree of Surface Disfigurement of Paint Films by Microbial (Fungal or Algal) Growth or Soiland Dirt Accumulation.

DIRT PICK-UPSee DIRT ACCUMULATION.

DIRT RESISTANCEThe ability of a coating to resist soiling.

DISBONDINGThe separation resulting from insufficient adhesion of a coating to an undercoating or othersubstrate.

DISCOLORATIONChange in the color of a coating after application (usually an undesired darkening), normallycaused by exposure to sunlight or chemical atmospheres.

DISCONTINUITIESSee HOLIDAY.

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FAILURE TERMS

DRAGResistance of paint to being spread by a brush. A paint with a lot of drag is hard to work witha brush.

DRIFTSee OVERSPRAY.

DRIPA drop of wet coating that forms on or falls from the edge of the coated substrate.

DRY SPRAY(1) A rough, powdery, noncoherent film produced when an atomized coating partially driesbefore reaching the intended surface; (2) Overspray or bounce back falling dry on unintendedsurfaces and producing an adherent, sand-like covering. See also BOUNCE BACK,OVERSPRAY.

DULLINGLoss of gloss or sheen. [AM]

DURABILITYDegree to which paints and paint materials withstand the destructive effect of the conditionsto which they are subjected.

E

EDGE FAILUREA type of coating adhesion failure in which undercutting (penetration of corrosion beneaththe coating) occurs at an unprotected or incompletely protected edge.

EFFLORESCENCEA white crystalline or powdery deposit on the surface of concrete. Efflorescence results fromleaching of lime or calcium hydroxide out of a permeable concrete mass over time by water,followed by reaction with carbon dioxide and acidic pollutants.

ELECTROENDOSMOSISPenetration of water through a coating film caused by excessive cathodic protection poten-tials. Often results in blistering of coatings.

EROSIONThe gradual loss of coating by wear or weathering. ASTM D 662 is the Standard Test Methodfor Evaluating Degree of Erosion of Exterior Paints.

EROSION-CORROSIONA joint action involving corrosion and erosion.

EXFOLIATETo separate in flakes, scales, or layers.

EXUDATIONThe migration of a substance to the surface, such as resin from wood, or plasticizer fromfilms. (CED)

F

FADEOMETERAn apparatus for determining the resistance of coatings and other materials to fading. It

197

FAILURE TERMS

accelerates the fading by subjecting coated panels to high-intensity ultraviolet wavelengthssimilar to those found in sunlight.

FADINGA cosmetic coating defect consisting of reduction in color intensity.

FAILURESee PAINT FAILURE, COATING FAILURE.

FAILURE ANALYSISAn investigation conducted to determine the causes and responsibilities of coating defects,loss of coating function, and/or corrosion, if present.

FALLOUT (SPRAY)See OVERSPRAY.

FILIFORM CORROSIONCorrosion exhibiting a thread-like structure and directional growth under coatings on metalsurfaces such as steel or aluminum. [Painting/Coatings Dictionary]

FIN(1) A narrow linear projection on a formed concrete surface, resulting from mortar flowinginto spaces in the formwork; (2) A type of blade in a concrete mixer drum. [ACI]

FISH EYEINGSee FISH EYES.

FISH EYESCoating film defects related to cratering in which small dimples or holidays resembling fisheyes form in the wet coating. See CRATERING.

FLAKINGThe detachment of pieces of the paint film itself either from its substrate or from paint pre-viously applied. Flaking is generally preceded by cracking, checking or blistering and is theresult of loss of adhesion usually due to stress-strain factors. ASTM D 722 is the standardtest method for evaluating degree of flaking of exterior paints. Also referred to as scaling.

FLAKING RESISTANCEThe ability of a coating to resist the actual detachment of film fragments either from thepreviously applied coating or the substrate. Flaking is generally preceded by cracking, check-ing, or blistering, and is the result of loss of adhesion. Also known as scaling resistance.[ASTM D-16]

FLASHINGThe occurrence on the surface of a coating film of patches glossier than the surroundingcoating. See HOT SPOTS.

FLEX-CRACKINGThe development of cracks in coating when subjected to repeated bending.

FLOATINGThe segregation of individual pigments in a coating system during curing related to differen-tial movement in surface tension currents caused by solvent evaporation. Produces a varigatedpaint surface.

FLOCCULATIONFormation of clusters of pigment particles in a fluid medium that may occur after dispersion.The condition usually is reversible, and the particle clusters can be broken up by applying

198

FAILURE TERMS

relatively weak mechanical forces or by a change in the physical forces at the interface be-tween the liquid and the solid dispersed particles. Flocculation is often visible as a “JackFrost” pattern in a flowout of a dispersion; microscopically, it appears as a lacework or reticu-lum of loosely clustered particles. It results in more rapid settling although it is usually soft,shows loss of color strength and poor dispersion. Surface-active agents are often useful inreducing the extent of flocculation and hence the yield value.

FLOODINGThe segregation of pigments in a coating system caused by different rates of settling in thewet film to form a uniform appearance different from that expected. Compare to FLOATING.

FOAMINGThe development of small air bubbles into liquid coatings during mixing. Latex coatings areespecially susceptible to this phenomenon because of their surface active agents used to sta-bilize the dispersion.

FOGGINGMisting. [AM]

FOREIGN MATTERAny material in a paint or varnish or on a coating film that does not belong there.

FOULING (BIOFOULING)Marine organisms, both flora and fauna, attached to the hulls of ships and other structuresin sea water that cause drag.

FRETTING CORROSIONThe accelerated deterioration at the interface between contacting surfaces as the result ofcorrosion and slight oscillatory movement between two surfaces. [ASM]

FROTHINGSee FOAMING.

G

GALVANIC CORROSIONAccelerated corrosion resulting from two dissimilar metals in electrical contact, exposed toconductive medium.

GELLING(1) A defect in which an oil or alkyd paint or varnish thickens to jelly-like consistency in anunopened container; (2) The first stage in the cure of an epoxy or polyurethane coating inwhich a soft, semisolid network is formed. See also LIVERING.

GHOSTINGA cosmetic coating defect occurring to low sheen finishes in which there are areas with lesscolor or difference in sheen from surrounding areas.

GLOSS RETENTIONAbility of a coating material to maintain its gloss.

GRAFFITIMarkings, slogans, or drawings that deface a wall or other surface.

GRAININESSA rough, bumpy, or sand-like texture in a dry coating film.

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FAILURE TERMS

GRINNING THROUGHShowing through of the underlying surface layer due to inadequate opacity of a paint filmwhich has been applied to it. [CED] See INCOMPLETE HIDING.

H

HACKLE(S)Thin, needle-like or sliver-like protrusions (ranging from 3 to 6 mils [76 to 152 micrometers])found on steel plates that have been blasted with steel shot or grit. [Painting/Coatings Dic-tionary]

HAIRLINE CRACKSVery fine cracks which do not penetrate the topcoat; they occur erratically and at random.[CED] See CRACKING.

HAZINGSee CLOUDINESS.

HEAT AGINGDeterioration of a coating as a result of exposure to elevated temperatures.

HEAT RESISTANCEThe ability of a coating to resist deterioration when exposed continuously or periodically tohigh temperatures at or below a given level. Heat resistance depends on the binder type andother coating ingredients.

HIDING PIGMENTA pigment with a high refractive index that gives the most hiding power to a coating. Rutiletitanium dioxide, followed by anatase titanium dioxide, zinc sulfide, and zinc oxide are mate-rials with high refractive indices.

HOLIDAYPinhole, skip, discontinuity, or void in a coating film that exposes the substrate. [ASTM]

HOLIDAY DETECTORInstrument utilizing electric current (low-voltage, high-voltage or AC electrostatic) to detectnicks, scrapes or pinholes (holidays) that penetrate a coating film.

HONEYCOMBVoids left in concrete due to failure of the mortar to effectively fill the spaces among courseaggregate particles. [ACI]

HOT SPOTSAreas of higher gloss than surrounding areas often caused by being relatively resin-richwhere coating was applied more thickly than other areas.

I

IMPACT RESISTANCEAbility of a coating to resist a sudden blow; ability to resist deformation from impact.

IMPACT STRENGTHSee IMPACT RESISTANCE.

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FAILURE TERMS

INCLUSIONPresence of foreign material in the finished material. [CED]

INCOMPATIBILITYInability of coating materials to perform satisfactorily when in direct contact with anothercoating or substrate. The incompatibility may be chemical (e.g., causing bleeding or saponi-fication) or physical (e.g., inability to expand and contract with substrate).

INCOMPLETE HIDINGFailure to completely obscure from vision any underlying coating or other substrate.

INDENTATION HARDNESSResistance to penetration by an indenter. [CED]

INTERCOAT CONTAMINATIONContamination between successive coats of paint or a coat of paint and the base substrate.

INTERCOAT DELAMINATIONThe separation (disbonding) of two adjacent coats of paint.

INTERCOAT DISBONDINGSee INTERCOAT DELAMINATION.

INTRACOAT ADHESIONCohesion within a coat of paint. The ability of a paint film to hold itself together. See COHE-SION.

INTRACOAT DISBONDINGSee COHESIVE FAILURE.

L

LAITANCEA thin, weak, brittle layer of cement and aggregate fines on a concrete surface. The amountof laitance is influenced by the type and amount of admixtures, the degree of working, andthe amount of water in the concrete.

LAP MARKSVisually darker section edges where paints or stains have dried before adjacent areas havetied into them, i.e., where a wet edge has not been maintained.

LEVELINGThe ability of a coating to flow out after application so as to obliterate any surface irregulari-ties such as brush marks, orange peel, peaks, or craters which have been produced by themechanical process of application.

LEVELING AGENTChemical added to coating to increase the ability of the wet film to settle to a uniform thick-ness.

LIFTINGSoftening and raising or wrinkling of a previous coat by the application of an additional coat.[Painting/Coatings Dictionary] Lifting often occurs because the solvents in the new coat aretoo strong for the previous coat.

LIVERINGThe progressive, irreversible increase in consistency of a pigment-vehicle combination.

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FAILURE TERMS

Livering usually results from a chemical reaction of the vehicle with the solid dispersedmaterial, but it also may result from polymerization of the vehicle. The irreversible charac-ter of the changes distinguishes livered material from thixotropic “build-up,” which is re-versible. [Painting/Coatings Dictionary]

M

MICSee MICROBIOLOGICALLY INFLUENCED CORROSION.

MICROBIOLOGICALLY INFLUENCED CORROSION (MIC)Corrosion that is affected by the action of microorganisms in the environment, e.g., sulfate-reducing bacteria found in some petroleum products and in sewage.

MILDEWMicroorganisms, particularly fungi, that grow on paint and other surfaces, particularly indamp, shady places, causing discoloration and disfigurement.

MILDEWCIDEAn additive used to enhance a coating’s ability to resist mildew growth.

MILDEW DEFACEMENTUnsightly appearance on coated or uncoated surfaces caused by growth of microorganisms,particularly fungi. ASTM D 3274 is the Standard Test Method for Evaluating Degree of Sur-face Disfigurement of Paint Films by Microbial (Fungal and Algal) Growth or Soil and DirtAccumulation.

MILDEW RESISTANCEA coating’s ability to resist the growth of mildew (fungus growth) on its surface.

MILKINESSWhitish or translucent appearance in an unpigmented liquid coating or film which shouldnormally be transparent. [CED]

MISSESHolidays, skips, voids. [AM]

MOTTLINGThe presence of differently colored spots or blotches on a surface.

MUD CRACKINGA coating defect resembling the irregular cracking of drying mud that typically arises duringthe curing of a relatively inflexible coating applied too thickly.

N

NATURAL WEATHERINGGradual deterioration of a coating as a result of exposure to an exterior environment, asopposed to artificial (laboratory) accelerated weathering.

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FAILURE TERMS

O

OFF COLORAn unacceptable variation of color from that desired or specified.

OIL CANNINGBowing of the edges of a steel plate due to thermal expansion and contraction or cyclic load-ing and unloading. Oil canning can lead to cracking of the coating at the edges.

OIL SOFTENINGThe conversion of a satisfactory coating into an unacceptably soft and tacky one, when incontact with household or industrial oils.

ORANGE PEELA coating application (usually spray) defect in which the coating surface has the irregularappearance of an orange skin because of insufficient leveling of the wet film. On productssuch as appliances, orange peel may be desirable.

OVERATOMIZEDDispersed too finely by use of excessive atomizing pressure. [AM]

OVERBAKINGAn exposure of the coating to a temperature moderately higher or for a longer period of time,or both, than that recommended by the manufacturer of the coating for normal curing, [CED]so as to adversely affect coating performance.

OVERCURECaused by an aftercure or being subjected to too high a temperature or too long a period at aproper temperature and resulting in a product with lowered performance. [CED]

OVERSPRAY(1) Atomized paint particles that deflect from or miss the surface being spraye; (2) Sprayparticles that are not wet enough to fuse when they reach the surface being sprayed. As aresult, overspray may contaminate property beyond the surface being sprayed. See also DRYSPRAY, BOUNCE BACK.

P

PAINT CHIPPINGSee CHIPPING.

PAINT FAILURESee COATING FAILURE.

PEELINGDisbonding of particles of paint, varnish, or lacquer film from a surface due to loss of adhe-sion. It may be caused by dampness, grease, an improperly prepared surface, or excessivemoisture behind the surface.

PERISHINGSee DETERIORATION.

PIGMENT OVERLOADUse of more pigment in a coating than can be completely wetted by the resin; exceeding the

203

FAILURE TERMS

critical pigment volume concentration (CPVC).

PINHOLEA holiday or discontinuity that extends entirely through a coating film, approximately thesize of a pin; normally caused by solvent bubbling, moisture, or foreign particles.

PINHOLINGFormation of small holes through the entire thickness of coating; see CRATERING. [AM]

PINPOINT RUSTINGTiny, dispersed points of rust that can appear at pinholes and holidays in a coating. Verydense pinpoint rusting can appear on painted steel surfaces where the coating does not com-pletely cover the blast cleaning profile.

PITA small hole in the surface of a metal or other material that is deeper than its diameter.

PITTING(1) Localized corrosion of a metal surface, confined to a point or small area, that takes theform of cavities [ASM]; (2) In concrete, pitting is localized disintegration, such as popout.[ACI]; (3) Formation of depressions (pits) in the surface of a coating often caused by theescape of gas or solvent vapor.

POCKMARKINGSee PITTING.

PONDINGThe accumulation of a liquid or paint in a shallow depression. [MPDA]

POPPINGFormation of blisters of solvent vapor in wet coating surfaces that break but do not levelbecause of too great a viscosity.

POROSITY(1) The ratio, usually expressed as a percentage of the volume of voids in a material to thetotal volume of the material including the voids [ACI]; (2) Small interconnected voids, suchas in concrete, which allow fluids to penetrate an otherwise impervious material.

PROTECTIVE LIFEThe length of time a coating system provides protection to a substrate.

R

RAIN SPOTTINGParticular case of water spotting caused by rain. [CED]

REBOUNDIn spraying of coatings, the atomized particles that bounce back from the surface being painted.See BOUNCE BACK, OVERSPRAY.

REDUCED SERVICE LIFELessened time during which the coating provides its intended function(s).

RETICULATIONA surface defect of net-like appearance. [AM]

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FAILURE TERMS

RETRACTIONSee CRAWLING.

ROPEYA quality of paint that does not flow out evenly and dries with slight ridges. This effect alsocan be the result of poor workmanship.

ROPY FINISHSee BRUSH MARKS.

RUNNINGSee SAGGING.

RUNSIrregularities of a surface due to uneven flow, frequently due to application of a coat that istoo heavy and not brushed out well. Also known as “sags” or “curtains.” [MPDA] See SAG-GING.

RUSTAn iron oxide that forms naturally on ferrous metals as a result of exposure to normal weath-ering or industrial atmospheres.

S

SAGGING(1) The irregular downward flow of wet paint under the force of gravity to produce a thickerlower edge. Thus, denser, thicker, and lower viscosity coatings are more likely to sag; (2)Subsidence of shotcrete, plaster, or the like, due generally to excessive water in the mixture;also called sloughing. [ACI]

SAGSee SAGGING.

SAG RESISTANCEThe ability of a wet paint film to resist the downward flow that results in an uneven filmwith thick edges and runs. See also RUNS.

SALT AND PEPPER RUSTINGSee PINPOINT RUSTING.

SALT FOG RESISTANCEResistance to deterioration during salt spray testing. See SALT SPRAY TEST in main glos-sary.

SANDY FINISHA surface condition having the appearance of sandpaper; overspray. [AM]

SAPONIFICATIONAlkaline hydrolysis of fats to form soaps.

SAPONIFICATION, COATINGThe akaline hydrolysis of coating binders (usually their drying oils) to disbond and degradethem. This commonly occurs on the alkaline surfaces of concrete and galvanizing.

205

FAILURE TERMS

SCALINGPaint failure that causes a coating to fall off in flakes or chips. Scaling is the last stage ofcracking. Moisture entering cracks in the paint film destroys its adhesive property and re-sults in the flaking or scaling of the paint. [PDCA]

SEDIMENTATIONAction or process of depositing matter (sediment) that settles to the bottom of a liquid.

SEEDINESSThe occurrence of particles in a coating formed from action of reactive pigments and acidiccomponents of the binder during storage that result in a roughened surface on the curedfilm.

SEEDINGFormation of small, undesirable particles or granules in a paint, varnish, or lacquer. [CED]

SEEDSSee SEEDINESS.

SEEDYDescriptive of a paint finish that is not smooth owing to undispersed pigment particles orinsoluble gel particles in the paint. [CED]

SEPARATIONDivision into components or layers by natural causes. [AM]

SETTLINGThe sinking of pigments, extenders or other solid matter in a paint in a container, with aconsequent accumulation on the bottom of the can.

SHADOWINGA coating of paint showing through a subsequent coating.

SHRINKAGEThe roughening of the surface of a coating resulting in loss of gloss or wrinkle.

SILKINGA surface defect characterized by parallel hairlike striations in coated films. [AM]

SISSINGSee CISSING.

SKINA solid or semisolid membrane that sometimes forms on paint or varnish in the can.

SKINNINGFormation of a thick film (skin) on the surface of a liquid paint during storage, more likely tooccur to a previously opened or partially filled container.

SKIPSHolidays; misses; uncoated areas; voids. [AM]

SOILINGSee DIRT ACCUMULATION.

SOLVENT ENTRAPMENTThe failure of solvent to completely evaporate from a paint film due to inadequate drying

206

FAILURE TERMS

conditions and/or recoating too soon. It may cause blisters or pinholes, sometimes called“solvent pop,” to form.

SOLVENT IMBALANCEA proportion of solvent types in a coating that causes inadequate solvency or improper evapo-ration rates.

SOLVENT POPSee SOLVENT ENTRAPMENT, POPPING.

SOLVENT RESISTANCEThe ability of a coating to resist solvent attack, solution or disfigurement. See SOLVENTRUB TEST in main glossary. [CED]

SOLVENT SHOCKThe situation wherein some of the protective vehicle is washed off the fine pigment particles,allowing them to pull together into clusters or flocs or when flocs of resin form due to dilutionwith a solvent or diluent of insufficient strength. [CED]

SPALLINGThe chipping or fragmenting of a surface or surface coating caused, for example, by differen-tial thermal expansion or contraction. [MPDA]. Spalling of a concrete surface also may re-sult from corrosion of rebar or other embedded steel.

SPATTER COATINGAn incomplete or not continuously wet coating caused by a faulty spray painting application.

SPECKLINGSee MOTTLING.

SPOTTINGDevelopment of small areas on a painted surface which differ in color or gloss from the majorportion of the work. [CED]

SPRAY MOTTLESee ORANGE PEEL.

STABLEResistant to change. In the case of corrosion, resistant to chemical reaction with oxygen.

STAIN(1) A solution or suspension of coloring material formulated to provide a color to a surface,especially wood, without completely hiding it or forming a continuous film; (2) An undesir-able surface coloration.

STAIN RESISTANCEThe ability of a coating to avoid change in appearance after a material capable of staininghas been applied and removed.

STREAKINGLong, narrow, irregular lines or bands or layer-edges, especially ones distinguished by color,visible on a surface. [CED]

SURFACE DRYINGDrying of the surface of a liquid coating film before the body of the coating film. The resultoften is that the under portion is slow in drying and that solvent is trapped within the coatingor the coating remains soft for an extended period of time. See TOP DRYING in main glos-

207

FAILURE TERMS

sary.

SWEATINGThe exudation of oil from a coating after it appears to have cured.

T

TACKThe stickiness of a surface such as a paint or varnish film during the drying period. Oilpaints and spar varnishes may retain tack for several weeks after they are considered dry.[PDCA]

TACK-FREEAbsence of tack or stickiness in an applied coating after suitable drying time. In some cases,coatings are tack-free after application; tack may not develop until a little later.

TELEGRAPHINGGeneral term used to describe surface defects such as crawling that give rise to unique pat-terns. [WJP]

THROUGH DRYINGUniform drying throughout the film as opposed to bottom-drying or top-drying.

TUBERCULATIONFormation of localized corrosion products scattered over the surface in the form of knob-likemounds.

U

UNDERCUREFailure of a coating to reach its optimum degree of cure, with a resultant loss of performanceproperties.

UNDERCUTTINGThe gradual penetration and spread of corrosion beneath a coating from a break or pinhole inthe film or from unprotected edges. Also referred to as creepage.

UNDERFILM CORROSIONCorrosion that occurs between a coating and the metal substrate without a break in thecoating layer.

UNEVEN LOSS OF GLOSSUneven loss of gloss is a cosmetic coating surface defect in which there is a variation inreduction of sheen such as may occur where there is partial shading.

USEFUL LIFEThe length of time a coating adequately performs its function. See SERVICE LIFE in mainglossary.

V

VACATIONSee HOLIDAY.

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FAILURE TERMS

VOIDSee HOLIDAY.

W

WATER SPOTTINGSee WATER STAINING.

WATER STAININGAny nonuniform change in appearance, including color, gloss, or sheen in the shape of spotsand streaks, resulting from the accumulation of water on or the contact of water with thepainted surface. It is apparent after drying. [CED]

WEATHERINGThe behavior of paint films when exposed to natural weather or accelerated weathering equip-ment, characterized by changes in color, texture, strength, chemical composition, or otherproperties. [CED]

WEATHERING CHAMBERAn apparatus in which specimen materials can be subjected to artificial and acceleratedweathering tests that simulate natural weathering by the use of controlled cycles of ultravio-let radiation, light, water, and heat. Electric arcs, fluorescent bulbs, or other sources of ul-traviolet light, water spray, and heating elements are used to simulate the natural condi-tions of sun, rain, and temperature changes.

WEATHERING CONDENSATION TESTA test that exposes coated specimens to a cycle consisting of fluorescent ultraviolet light andcondensing humidity to accelerate the effects of sunlight and moisture.

WEATHER RESISTANCEThe capability of a coating to resist the combination of exposures created by weather, such asheat, cold, thermal cycling, rain, and sunlight.

WEBBINGSee WRINKLING.

WHITE RUSTWhite oxidation products (oxide, hydroxide, carbonate) of zinc formed on galvanized andother zinc coated surfaces.

WRINKLINGA defect that creates small furrows or ridges in a coating film. Wrinkling usually occurs withthick films of oil-based paint.

Y

YELLOWINGThe formation of a yellow color or cast on a white or light-colored coating.

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CORROSION MANAGEMENT July 2000

by CM Staff

based on information supplied by Wattyl Paints

INTRODUCTION

Recognising the type of paint failure encountered inthe field is an important mechanism in ensuring qualitycoatings and coating application. Identification ofcauses of problems can be fed back into thespecification and application process to avoidrepetition of failure events.

Causes of paint coating failure are frequentlyassociated with either:

• incorrect specification• faulty material• incorrect application• incorrect curing/post handling procedures.

All paints eventually fail by weathering and the lifeexpectancy of a paint system will be well defined bythe manufacturer or within performance standardssuch as AS/NZS 2312 - Guide to the Protection ofIron and Steel from Atmospheric Corrosion.

Those that fail prematurely will have done so becauseof an identifiable problem associated with theirapplication.

A great deal of research has gone into painttechnology development by the major Australian andinternational paint companies as they compete witheach other and with other coatings and materials toproduce better performing products.

Environmental pressures on paint manufacturers toeliminate potentially hazardous pigments and reducethe amount of volatile organic greenhouse-causingsolvents in paint coatings has accelerated thedevelopment of new types of paint coatings.

Water based, low solvent or solventless coatings havereplaced many of the standard industrial coatings ofyesteryear. Hybrid organic/inorganic binder systemshave also been developed that, while expensive, offeradvances in durability over traditional technologies.

Again, AS/NZS 2312 provides one of the mostvaluable reference works for paint coatings and paint

systems, with detailed descriptions of a wide rangeof generic paint types, their suggested uses andcharacteristics.

In some cases, paint failures can be traced to theincorrect selection of paint for the particularapplication.One of the most common examples ofincorrect paint selection is the use of alkyd (oil based)paints, for painting galvanized coatings.

The paint reacts with the zinc in the galvanized coatingand loses its adhesion, resulting in the commonphenomenon of flaking or peeling paint.

Many paints have poor UV resistance, and again, oilbased paints, unless they are specially formulated willrarely give the same durability as water-based acrylicpaints, which have excellent UV stability over time,or two-pack uretahne or acrylic systems.

Water based acrylic paints have very goodcompatibility with galvanized coatings and rarely haveadhesion problems on properly prepared surfaces.

Industrial or marine applications are criticalapplications where the performance requirements ofthe paint system must be clearly understood.

Epoxy coatings are often considered the cure-all formost industrial applications, but may perform poorlyin highly acidic exposures or where movement orvibration may result in cracking of the relativelyinfexible paint film.

It is therefore important for specifiers to clearlyidentify the environment in which the coating has tooperate and ensure that paint systems selected arecapable of delivering the life cycle performanceexpected.

There is always a reason for every coating failure,and frequently, coating defects do not always affectthe coating’s performance, but only its appearance.

The following catalogue of paint defects has beenassembled with associated descriptions of causes andremedies to assist in identifying problems and dealingwith them to ensure a quality coating.

�������� �� ���� ����� ��������� �� ���� ����� ��������� �� ���� ����� ��������� �� ���� ����� ��������� �� ���� ����� �

22

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CORROSION MANAGEMENT July 2000

DESCRIPTION

SAGS - also called runs or curtains.Excess flow of paint

ORANGE PEEL - hills, valleys inpaint resembling skin of orange

OVERSPRAY - also called dry spray.Dry, flat, pebbly surface

COBWEBBING - thin, stringy paint,spider web-like particles

CRATERING - also called pitting.Small, uniform identations in film

FISH EYES - separation or pullingapart of wet film to expose underlyingfinish or substrate

BLUSHING - flat finish with milkyappearance

UNEVEN GLOSS - non uniformsheen, shiny spots

FADING - colour changes orirregularities

WRINKLING - rough, crinkledsurface

BLISTERING - small to large brokenor unbroken bubbles

PINHOLING - tiny, deep holesexposing substrate

PINPOINT RUSTING - rusting atpinholes or holidays

CAUSE

Spray gun too close to work; toomuch thinner; too much paint; orsurface too hard or glossy to holdpaint.

Paint too viscous; gun too close tosurface; solvent evaporated too fast;or air pressure too low for properatomization.

Particles reaching surface not wetenough to level because of too rapidsolvent evaporation; gun too far fromsurface; or paint particles fallingoutside spray pattern.

Solvent evaporating too rapidly.Most common with fast evaporatinglacquers, such as vinyls andchlorinated rubbers.

Air pockets trapped in wet film duringspraying.

Application over oil, dirt, silicon, orincompatible coating.

Moisture condensation in highhumidity with fast evaporating orunbalanced thinner in sprayapplication.

Non uniform film thickness; moisturein film. Temperature change duringcuring; or paint applied over soft orwet undercoat.

Ultraviolet light degradation; ormoisture behind paint film.

Surface skinning over uncured paintbecause of too much thickness and/or too warm weather, especially withoil-based paints.

Solvent entrapment; oil, moisture orsalt-contaminated surfaces; orcathodic disbonding.

Insufficient paint spray atomization;coarse atomization; or settledpigment.

Pinholing or too high a steel surfaceprofile for coating thickness.

REMEDY

Before cure, brush out excess paintand modify spray conditions. Aftercure, sand and apply another coat.

Before cure, brush out excess paintand modify spray conditions. Aftercure, sand and apply another coat.

Before cure, remove by dry brushingfollowed by solvent wiping. Aftercure, sand and apply another coat.

Use slower evaporating solvent orapply when cooler. After cured, sandand apply another coat.

Sand or blast to smooth finish andapply additional coats.

Sand or blast remove; brush apply afresh coat plus topcoat.

Sand or blast remove; respray withretarder added to thinner.

Allow to dry and apply another finishcoat under acceptable conditions formoisture and humidity.

Repaint and avoid possible sourcesof moisture.

Scrape off wrinkles and apply thinnercoat; avoid intense sunlight.

Blowers in enclosed areas toaccelerate solvent release; adequatecleaning of surface contamination;proper levels of cathodic protection.

If uncured, brush out and applyadditional coat. If cured, applyadditional coat.

Use holiday detector for earlydetection of pinholes; applyadditional coats after mechanical orblast cleaning.

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CORROSION MANAGEMENT July 2000

DESCRIPTION

CHECKING - narrow breaks, usuallyshort, in topcoat that exposeundercoat

CRACKING - deep cracks in paintthat expose substrate

UNDERCUTTING - blistering and/or peeling of paint where exposedsteel is rusting

DIRT UNDER PAINT - peeling; dirtdried in paint film

DELAMINATION - peeling fromundercoat or substrate

PIGMENT OVERLOAD - also calledpigment float, mottled surface

IRREGULAR SURFACEDETERIORATION - deterioration atedges, corners, crevices, channels,etc.

ABRASION DAMAGE - mechanicaldamage

FOULING DAMAGE - penetration orpeeling by action of marine foulingorganisms

MUD CRACKING - deep, irregularcracks as with dried mud

PEELING OF MULTIPLE COATS -peeling of heavy paint build-up fromsubstrate

PEELING OF THICK, INFLEXIBLEPAINT - peeling of thick paint fromsubstrate

PAINT APPLIED TO DAMPSURFACE - heavy wrinkling

MOISTURE DAMAGE - peeling ofpaint by underlying moisture

REMEDY

Sand or mechanically removechecked coat and apply another coat.

Sand, blast, or mechanically removetotal paint and apply new coat.

Early detection of defects withholiday detector and correction; useinhibitive pigments in primer.

Sand, blast, or mechanically removepaint and re-coat.

Sand or mechanically remove allloose paint, clean and roughensmooth surface, and re-coat.

Apply properly prepared finish coat.

Round edges; fillet weld seams andcrevices; avoid configurations thatpermit collection of contaminants;provide drainage.

Provide fendering protection; spotrepair and use more abrasion orimpact-resistant coatings.

Remove and replace damaged paint withone tougher or more adherent; use anti-fouling paints for fouling control.

Remove coating and abrasively blaststeel before reapplying lesser thickness;sanding/mechanical cleaning may beacceptable on older substrates.

If limited, spot-remove loose paintand apply flexible paint (e.g. latex); ifextensive, scrape, sandblast,mechanically or chemically removepaint to substrate before re-coating.

Same as above

Remove by scraping or sanding andre-coat under dry conditions.

Use wedges between adjacent lapboards, vents, etc, for migration;clean painted vent holes.

CAUSE

Limited paint flexibility; too thick acoat; or applied at too high atemperature.

Paint shrinkage; limited flexibility;excessive thickness (especially zinc-rich paints); or applied/cured at toohigh a temperature.

Corrosion products formed wheresteel is exposed, undermining andlifting paint.

Contaminated surface, spray, or workarea.

Separation/lifting of paint fromchalky substrate or smooth, poor-bonded undercoat.

Critical pigment level exceeded(sometimes by tinting white paintrather than tint base).

Difficult to coat surfaces; orconfigurations that permit collectionof moisture, salt, and dirt.

Physical damage by abrasion (alsoimpact).

Barnacles, etc, penetrating softcoatings (eg. coal tar); weight offouling peeling poorly bonded paint.

A relatively inflexible coating appliedtoo thickly (especially common withinorganic zincs).

Stress from weathering (contractionof total system) exceeds adhesion tosubstrate.

Stress from cured, weathered(contracted) paint exceeds adhesionto substrate.

Moisture on substrate distorts wetfilm.

No means by which interior moisturecan be vented to exterior.

24

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CORROSION MANAGEMENT July 2000

DESCRIPTION

EFFLORENSCENCE DAMAGE -paint disbonding and peeling byloose, powdery material

VINE PENETRATION OF PAINT -vine tendrils penetrate paint

MILDEW GROWTH - black fungalgrowth

CHALKING EROSION - gradualthinning of finish coat to exposeundercoat

BLEEDING - brown staining of paintin asphalt or coat tar coating

SKINNING/DETERIORATION OFSTORED PAINT

CAUSE

Moisture through concrete,masonry, or brick picks up solublesalts and deposits them on thesurface from the interior (can be oninterior or exterior well of building).

Vines so close to structure thattendrils penetrate paint for support.

Microorganisms grow, especially ondamp, shaded paint, defacing anddegrading it.

Degradation of coating resin bysunlight leaving loose residue;especially bad with thin coats,epoxies, and substrates where chalkis frequently removed.

Organic solvent in wet paint or freshasphalt dissolves bituminousmaterial and causes it to migratethrough paint.

Improper storage of paint (e.g. in sunand rain), especially fast dryingpaints.

REMEDY

Treat as in NCEL Tech Data Sheet77-10 or NAVFAC MO-110, 4.4.3.5 forconcrete/masonry before painting;seal more humid side of wells.

Relocate vines away from structure;sand and re-coat damaged areas.

Clean and repaint as described inNAVFAC MO-110,10.3.2.5 and10.2.2.73

Remove loose chalk and apply chalk-resistant finish coat.

Use latex paint over bituminousmaterials; allow asphalt pavementsto cure 21 days before applying paint.

Store indoors in cool environment;avoid opening and resealing of largecontainers.

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CORROSION MANAGEMENT July 2000

26

Description: Flaking paint over gal-vanized surface.

Cause: Incorrect surface preparation.Incorrect primer/topcoat.

Remedy: Remove flaking paint byscraping or wire brushing. Highbpressure water wash surface. Applyappropriate water based or epoxypriming systems.

Description: Flaking two-packepoxy paint on crane rails in galva-nizing plant pre-treatment building.

Cause: Low pH condensation (pH1)and flexing and vibration of cranerails in service cause brittle paintfilm to crack and promote underfilmcorrosion.

Remedy: Wet abrasive blast back toremove surface contamination andold paint. Apply flexible, acid resist-ant recoatable mastic type coating

Description: Efflourescence bleedingthrough pinholes in paint film in ma-rine exposure.

Cause: Pinholes in paint film causedby solvent entrapment or single coatapplication.

Remedy: Ensure piant is currectlyapplied and cured. Use multi-coatsystem to eliminate pinholes.

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CORROSION MANAGEMENT July 2000

27

Description: Underfilm corrosion indefined regions of coating.This largetank has areas of clearly defined paintsystem performance.

Cause: Area on far left has severelocal underfilm corrosion indicatinginitial poor surface preparation/prim-ing. Centre zone is in good condi-tion. Right hand zone shows generaloverall deterioration consistent withnormal weathering but ealy failureindicative of low initial dry film thick-ness for the system.

Remedy: Apply as for centre zone.

Description: Early failure of mainte-nance topcoat system along beamedges.

Cause: Adhesion of old paint insuffi-cient to accommodate surface tensioneffects of new two-pack system epoxytopcoat.

Remedy: Completely remove old paintprior to re-coating or use moreflexibible re-coating system compat-ible with old paint.

Description: Blistering of paint onhandrail.

Cause: Areas of contamination on sur-face interfering with primer adhesion.

Remedy: Ensure surface cleanlinessprior to application. On existing item,mechanically remove any blisteredareas and feather back to sound paint.Re-apply primer and topcoat.

Chapter 12Coating Failures

Richard W. Drisko

IntroductionAll coatings have limited service lives. Unfortu-

nately, there are occasions when coatings fail muchsooner than they should. When this occurs, it isnecessary to determine the causes of the failure andwhat actions must be taken to correct this conditionand prevent its recurrence.

There are numerous causes of coating failure.These may be related to structural design, the sub-strate, the coating itself, surface preparation, coatingapplication, or coating curing, or combinations of thesebasic causes. Historically, improper or inadequatesurface preparation has been the most commonlyreported cause of coating failure; more recently,governmental restrictions on coating VOCs and toxicconstituents (e.g., solvents, pigments, and biocides)have restricted coating formulations and made themmore difficult to apply successfully. This chapter willaddress the common causes of coating defects onindustrial structures and the associated preventative orcorrective actions.

Commonly Used Failure Terms Many different terms commonly used to describecoating failures mean different things to differentpeople. SSPC’s Protective Coatings Glossary definesfailure terms and these definitions are used for allfailure terms in this chapter.1 Some of the definitions ofgeneral terms commonly associated with coatingdeterioration/degradation are:Catastrophic Coating Failure. A coating failure that issudden, very dramatic, and serious.

Defect. A surface or film imperfection (flaw), deficiency,or incompleteness that deviates from a specification orindustry-accepted condition.

Degradation. A gradual loss of coating materials and/orproperties resulting from service conditions andweathering.

Deterioration. See degradation above.

Failure of Coating. Loss of a coating’s function orpurpose, i.e., when it no longer protects the substrate,provides an attractive appearance, or serves someother function such as providing a non-slip surface.The time of failure is considered to occur when someaction is needed to restore its properties to the levelnecessary to again provide its intended purpose(s).

Failure Analysis. Systematic investigation conductedto determine the causes and responsibilities of coatingdefects, loss of function, and/or corrosion, if present.

Premature Failure. Failure that occurs significantlybefore a coating’s life expectancy.

Service Life of Coating. The period of time duringwhich a coating provides its intended function(s). Thiswill vary with different exposures and services.

Effects of Structural Design on Metal andCoating Deterioration

It has been shown that structural design maybe an important factor in metal and coating deteriora-tion.2-3 It is important that these design factors berecognized and corrected at the planning stage ratherthan later when their adverse effects have becomeapparent. Although each of the major design factorsleading to early coating deterioration will be discussedseparately, they often occur in conjunction with otherfactors that further aggravate the deterioration.

Contact of Dissimilar Metals Resulting in GalvanicCorrosion

When two dissimilar metals are in physicalcontact with each other in an electrolyte (electricallyconductive medium), the more active metal willcorrode preferentially, while protecting the other metalfrom corrosion. The greater the difference in electro-chemical activity between the metals, the greater willbe the rate of dissimilar metal corrosion. The relativesurface areas of the touching metals may also greatlyaffect the corrosion of the more active metal (the

anode in the reaction). A small anode area and a muchlarger cathode (protected) area may result in ex-tremely rapid corrosion of the smaller anode area.Thus, in painting, care should be taken to ensure thatall cathode areas are especially well covered. Galvaniccorrosion may also be minimized by using metalsof similar composition, or using a non-conductiveinsulator between them.

CrevicesCrevices are likely to occur in structural

components that are bolted, riveted, or skip-weldedtogether. Inside crevice areas, there is invariably alower concentration of oxygen as compared to the airoutside the crevice. This results in a corrosion cell withaccelerated corrosion occurring within the crevicearea. Thus, continuous welding is the preferredmethod of joining metal components. Welds shouldbe ground smooth and weld spatter removed beforecoating in order to obtain good coating adhesionin these areas. Also, back-to-back angle designsshould be avoided because they have crevicesbetween them.

Water TrapsWater traps are design features, such as

upward facing angle iron, that collect the rain thataccelerates deterioration of coatings and corrosion ofmetals. Such designs should be oriented downward sothat the water drains. Drill weep holes into existingwater traps to permit collected water to drain.

Sharp EdgesWhen sharp edges are coated, the paint tends

to draw back from the edge to leave a much thinnercoat of paint there than on flat areas. In order toproduce a coating film of more equal thickness (andthus equal barrier protection) on all surfaces, edgesare usually striped (brushed with an additional coat ofprimer) before or after applying a full coat to thesubstrate. Relatively recently, new edge-retentivecoatings (usually amine-cured, solvent-free epoxies)have been developed to address this problem.

Faying SurfacesFaying surfaces are contacting surfaces where

joints in steel structures are formed by riveting or bythe use of high-strength bolts. Most coatings areunsuitable for use in the joint itself, because they do

5

not provide the proper coefficient of friction to maintainthe joint in a static state. However, inorganic zinc-richsilicate coatings have adequate coefficient of friction toperform well in this service.

Limited Access to WorkLimited access to surfaces to be cleaned

and coated often results in poor quality work andconsequently early coating deterioration. Thus,structures should be designed for access both forthe original work and for subsequent maintenancepainting.

Effects of Substrate Properties on CoatingPerformance

It has been shown that the chemical andphysical natures of a surface to be coated may have avery profound effect on the performance of the coatingsystem.4 It should be noted that, in general, texturedsurfaces provide more bonding sites and thus havegreater coating adhesion than smooth areas of similarcomposition.

Hot-Rolled SteelMost structural steel is made by the hot-rolling

process. This process results in a loosely bonded layerof iron oxide called mill scale. Mill scale must beremoved before the steel is coated, or its subsequentloss with time will result in coating deterioration.

Coatings on metal structures are susceptibleto underfilm corrosion. Undercutting of a coating filmby corrosion at breaks or pinholes in the barrier filmmay result in rapid loss of coating and its protection.

Cold-Rolled SteelCold-rolled steel is used more for manufactur-

ing office furniture, appliances, and automobile bodiesthan for applications where structural strength isrequired. Cold rolling produces a denser, smoothersurface than hot-rolling. Coatings do not bond as wellto these surfaces. Thus, chemical treatments such asphosphating are often used to promote coating adhe-sion. Abrasive blasting can also be used to produce aprofile to improve coating adhesion.

High-Strength Alloy SteelsIn some environments, high-strength alloy

steels may require a coating system to supplement itsnatural corrosion resistance. In these cases, the

54

cleaning requirements are similar to those of conven-tional steels, but harder abrasives (e.g., siliconcarbide, aluminum oxide, or garnet) may be necessaryto produce the desired surface profile. Because oftheir inherent corrosion resistance, they will normallyhave less corrosion and undercutting of coating atfilm holidays.

Figure 1. Corrosion undercutting of coating at scratch.

Zinc-Coated SurfacesZinc-coatings, both galvanizing and zinc-rich,

always have alkaline surfaces created by the naturalcorrosion of zinc. This alkalinity will saponify (hydro-lyze) alkyds and other coatings that cure by oxidationof drying oils.

New galvanized surfaces are sometimes givena thin coat of oil or chromate conversion coating toprotect them from corrosion called wet storage stain orwhite rust during exterior storage. These treatmentsmust be removed prior to coating to permit goodcoating adhesion. The oil is best removed by solventcleaning (i.e., SSPC-SP 1), and the chromate conver-sion coating can be removed chemically or byprolonged weathering.

AluminumEpoxies normally bond quite well to

aluminum. For other coatings that do not, one the

following treatments may be used:• Chemical treatment such as phosphating• Wash priming (good with alkyds)• Blasting with a soft abrasive (e.g., plastic) to producea suitable profile

Aluminum is susceptible to exfoliation, anadvanced stage of intergranular corrosion character-ized by a delamination of metal along grain bound-aries. Rolled metal products such as aluminum alloyplate are especially susceptible to exfoliation due totheir longitudinal grain structure.

Coated aluminum is particularly susceptible toa form of corrosion called filiform. It is characterized bythreadlike directional growths proceeding away fromdamaged areas. In the past, chromate inhibitivepigments were widely used to control filiform corrosion;chromate-free inhibitive pigments are now used.

Figure 2. Filiform corrosion.

ConcreteConcrete has unique properties (e.g., alkalinity

and porosity) that make its coatings especially suscep-tible to certain defects. These are described exten-sively in SSPC’s The Fundamentals of Cleaning andCoating of Concrete.5

WoodThe properties of woods vary greatly with the

types of tree from which they came. Soft woods suchas redwood and fir are penetrated by coatings topermit good bonding much more easily than are hard(dense) woods such as ash and oak.

Pine and fir have variable grain structures,while redwood and cedar have uniform grain andbrown color. The brown color of the latter two woodscomes from water-soluble dyes that may bleedthrough latex coatings to cause staining, unless sealed

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before painting. An oil-based or water-borne stain-blocking primer can be used for this purpose.

Resinous materials in some trees, such aslower grades of pine, may seep to the wood surfaceafter painting to cause staining and paint deterioration.This can be minimized by using weathered wood andsealing it before use.

Woods are very sensitive to moisture so thatthey swell during periods of high humidity and shrinkduring periods of low humidity. Rigid coatings on woodmay crack when they are unable to expand andcontract with dimensional changes.

Coatings hide wood grain and greatly reducewater permeability. However, water that enters into thewood interior may try to escape through impermeablecoatings to cause blistering and/or delamination. Forthis reason, latex coatings that permit the passageof water vapor (sometimes called breathing) mayminimize this problem. Many people prefer to usesemi-transparent stains that do not seal the surfacesof wood.

Defects/Failures Associated with theCoating Itself

Some coating defects and failures are directlyrelated to the coating itself. These include:• Errors by the manufacturer in production ofthe coating• Coatings that have exceeded their shelf life• Inherent limitations of properly formulated coating• Incompatibility of a coating with its substrate orundercoat

Coatings with Errors in Manufacture or that HaveExceeded Their Shelf Life

Errors in coating manufacture do not occurvery often. They can usually be detected in the fieldbefore use by testing for condition in container, asdescribed in Federal Test Method Standard 141. If theviscosity does not appear to be at the proper level, itcan be checked in the field using a viscosity cup. Also,a test patch of coating can be applied to the intendedsubstrate to check for such properties as ease ofapplication, hiding, leveling, and complete curing.

If a stored coating has exceeded its shelf life,it may have deteriorated to the extent that it can nolonger be successfully utilized. Such coatings shouldbe checked for condition in container before use.

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Limitations of Coating FormulationsAll coating formulations have some limitations

that restrict their uses to appropriate environments andservices. In this section, some of the more importantlimitations are addressed.

Figure 3. Chalking.

Chalking. Chalking is the formation of loose powder onthe surface of coatings. It is typically caused bydeterioration of the organic coating binder by ultravio-let light (usually from the sun) to leave a loose residueof pigment and oxidized binder. All organic coatingbinders chalk to some extent, but those containingaromatic chemical groups (e.g., epoxies and pheno-lics) chalk much faster than others.

Some pigments such as the anatase form oftitanium dioxide chalk very freely, while other pigmentssuch as rutile, another crystalline form of titaniumdioxide, are quite chalk-resistant. Opaque pigments,of course, reduce chalking of underlying organicbinders by shielding them from sunlight. Leafingaluminum pigments formulated to float to coatingsurfaces protect underlying binders especially well.

Chalking of finish coatings can best becontrolled by proper selection of pigments and bindersand by use of additives such as ultraviolet lightabsorbers.

Erosion. Erosion is the gradual loss of coating by wearor weathering. Thus, coatings that chalk freely aremore susceptible to erosion than are coatings that aremore chalk-resistant. Erosion may also be caused bywind-blown sand or rain.

Accelerated erosion may significantlyreduce coating thickness and even expose under-coats. Erosion may be minimized by selecting a

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chalk-resistant coating with good leveling properties.

Figure 4. Erosion of topcoat on deck of a ship.

Discoloration. Discoloration is the change in coatingcolor after application (usually an undesirable darken-ing), normally caused by exposure to sunlight orchemical atmospheres. Thus, lead pigments areblackened by the attack of hydrogen sulfide gas. Tominimize discoloration, coating formulations shouldhave stable pigments and binders.

Fading. Fading is the reduction of color intensity,usually by sunlight. This adverse cosmetic effect canalso be minimized by using formulations with stablepigments or binders.

Loss of Gloss. Loss of gloss is still another defect thatis caused by sunlight and can best be minimized byselecting ultraviolet-resistant coating components. Allcoatings lose gloss in sunlight to some extent, butsome do much more than others. This cosmeticdefect, as well as discoloration and fading, is espe-cially distracting when it occurs on the side of astructure that is partially shaded so that there is anuneven loss of gloss or color.

Mildew Defacement. Mildew defacement is an un-sightly appearance on coated or uncoated structurescaused by the growth of micro-organisms, particularlyfungi. This is more of a cosmetic effect than one thatadversely affects coating film properties. Mildewdefacement may be controlled in architectural coatings(i.e., drying oil and water-borne latex coatings) byusing EPA-approved mildewcides. Also, smooth,chalk-free coating surfaces in dry locations exposed tosun light are less susceptible to mildew than othercoated surfaces.

Figure 5. Uneven loss of gloss.

Figure 6. Mildew defacement.

Moisture Blushing. Moisture blushing is the formationof a milky opalescence that may occur in humidenvironments where solvent evaporation reduces thetemperature of an uncured coating to the dew point sothat moisture condensation occurs on it. This cosmeticdefect most commonly occurs with fast evaporatingcoatings such as vinyl lacquers. Moisture blushingmay also occur by the reaction of moisture in the airwith polyurethanes and other moisture sensitivecoatings on humid days. Moisture blushing can best

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be prevented by avoiding the application of moisture-sensitive coatings on humid days.

Figure 7. Moisture blushing.

Amine Blushing. Amine blushing is the formation of amilky opalescence on the wet-film surfaces of amine-cured epoxies by the reaction of the amine with carbondioxide and water in the air to form an amine carbam-ate. This film may cause adhesion problems fortopcoats if not removed as recommended by theepoxy manufacturer.

Figure 8. Brush marks.

Brush Marks. Brush marks may occur in brush-applied coatings with insufficient leveling for thewet film to flow together to form a film of uniformthickness. Localized areas of lesser film thicknessalmost always exhibit deterioration before areas of

greater film thickness.

Orange Peel. Orange peel is similar to brush marks inthat it is caused by insufficient leveling of the wet film.However, this defect occurs with spray rather thanbrush application of coatings.

Figure 9. Orange peel.

Wrinkling. Wrinkling is a defect that results in theformation of small furrows or ridges in coating films. Itoccurs most commonly with thick films of alkyds andother drying oil-curing coatings. In these cases, curingby air oxidation occurs much more rapidly at thecoating surface than below it, and a surface skin isformed that prevents further curing of the underlyingbinder. Contraction of the surface skin causes thewrinkling. Through-dry metal driers will help acceleratecomplete film curing, but the use of lead driers (someof the best through-driers) is now greatly restricted.Wrinkling can also be minimized by avoiding thickerfilm than recommended by the manufacturer.

Chemical Attack on Coatings. Chemical attack oncoatings will occur when the coating system is notresistant to the environment. This most commonlyoccurs to linings in storage tanks where they comeinto contact with stored chemical liquids. Chemicalattack may also occur in atmospheric service whereharsh chemical fumes or vapors come into contact

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with the coating.

High-Temperature Attack on Coatings. High-temperature attack is likely to occur to organic coat-ings even during intermittent high-temperature service.Thus, heat-resistant inorganic coatings are usuallyused at temperatures above 450°F (230°C).

Figure 10. Wrinkling.

Figure 11. Mottling.

Mottling. Mottling is the presence of differently coloredspots or blotches on a painted surface. It is commonlycaused by pigment overload (using more pigment thancan be completely wetted by the limited amount ofresin present).

Osmotic Blistering by Soluble Pigments. Osmoticblistering may occur to coatings with primer pigments

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having significant water solubility. This is especiallylikely to occur during water immersion service. Thesepigments can be detected during a laboratory failureanalysis of the water (sometimes colored) in filledblisters.

Osmotic blistering may also occur if solublesalt contaminants are not completely removed fromsubstrates during surface preparation.

Flooding and Floating. Flooding and floating are twocosmetic formulation defects that are sometimesconfused with each other. Flooding is the segregationof pigments in a coating system caused by differentrates of settling in the wet film to form a uniformappearance different from that expected. Floating isthe segregation of individual pigments in a coatingsystem during curing related to differential movementin the surface tension currents caused by solventevaporation to produce a varigated paint surface.

Figure 12. Cracking.

Cracking. Cracking is a general term for the splitting ofa coating film to relieve stresses. Most of thesestresses originate by shrinking during curing, bysolvent evaporation, and/or polymerization. Stressesincrease with further polymerization and weathering.When stresses exceed the cohesive strength of thecoatings, they crack to relieve the stress.

The greater the coating thickness, the morerigid it is and thus the greater its tendency to crack.Different types of cracking, other than commoncracking, include hairline cracking, checking, crazing,

alligatoring, other intercoat cracking, and mud crack-ing. Cracking usually occurs all the way through thecoating to expose the substrate.

Figure 13. Checking.

Checking. Checking is the fine surface cracking thatdevelops in coating films during prolonged curing and/or weathering that does not penetrate to the underlyingsubstrate. Wetting and drying, heating and cooling,and exposure to sunlight all contribute to checking.

Alligatoring. Alligatoring is a type of crazing or surfacecracking with a definite pattern, as indicated by itsname. The effect often occurs when a relatively rigidcoating is applied over a more flexible undercoat. Theresulting stresses cause the topcoat to crack toexpose the undercoat but not the substrate.

Intercoat Cracking. Cracking from intercoat stressesmay occur when a relatively rigid topcoat is appliedover a more flexible undercoat. These stresses aresimilar to those previously described for alligatoring,but cracking does not always occur in such a regularpattern.

Mud Cracking. Mud cracking is a cracking pattern thatresembles the irregular cracking of drying mud. Ittypically occurs when a rigid coating is applied toothickly. This defect often happens with inorganic zinc-rich coatings, which are very rigid.

Figure 14. Alligatoring with bleeding.

Figure 15. Mud cracking of inorganic zinc-rich coating.

Coating IncompatibilitiesIncompatibilities may occur between individual

coats in a total coating system or between an existingsystem and a topcoat to be applied over it. It is wiseto obtain all coatings for a total system that are knownto be compatible with each other and that areproduced by the same manufacturer. Five types of

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incompatibility between coatings are described here.

Topcoat Solvent Attack on Undercoat Binder. Topcoatsolvent attack on undercoat binder may cause thelatter to soften, swell, or disbond. In any case, theintercoat adhesion is significantly diminished. Anexample of this is a chlorinated rubber or an epoxycoating with a strong solvent being applied over a vinyldispersion (latex) coating.

Figure 16. Bleeding of alkyd coating on asphalt

pavement.

Bleeding. Bleeding often occurs when a topcoat with astrong solvent is applied to a coal-tar or asphaltcoating. The solvent dissolves some of the coloredmaterial in the existing coating and allows it to migratethrough the topcoat to impart a brown surface discol-oration. This defect is somewhat similar to the previ-ously described bleeding from an asphalt pavementand migration of water-soluble dyes from woodthrough latex coatings.

Limited Adhesion. Limited adhesion and subsequentpeeling may occur to a water-dispersed (latex) coatingapplied over a smooth oil-based enamel. There isoften insufficient solvent in the topcoat to penetrate theexisting coating to achieve good intercoat adhesion.

Intercoat Cracking. Cracking from intercoat stresseswas described earlier in the discussion of different

forms of cracking.

Saponification (hydrolysis). Saponification may occurto an alkyd or other drying oil applied over a zinc-richprimer. As with concrete, the surface alkalinity on thezinc-rich primer causes this chemical degradation.

Figure 17. Saponification of alkyd coating.

Incompatibilities with Cathodic ProtectionThere are three basic mechanisms by which

coatings may be deteriorated by cathodic protectionsystems. Coatings to be used in conjunction withcathodic protection to control the corrosion of steelmust be resistant to these problems.

Saponification of Coatings. Alkalinity is always pro-duced on cathodically protected surfaces. If coatingson these surfaces are not alkali-resistant, they aresubject to saponification.

Blistering of Coatings by Hydrogen Gas Evolution.Blistering of coatings by hydrogen gas evolution mayoccur on cathodically protected surfaces where thevoltages are excessively high (e.g., in excess of–1.1 volts). This seldom occurs if steel-to-soil or

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steel-to-water potentials are regularly monitored.

Electroendosmosis. Electroendosmosis is a mecha-nism of coating deterioration in which excessivecathodic potentials causes electrolyte to penetraterapidly through a coating film. It normally results incoating blistering and peeling.

Coating Defects/Failures from InadequateSurface Preparation

Inadequate surface preparation is generallyrecognized as being the chief source of coatingdefects and failures. Surface preparation inadequaciesare either caused by inadequate removal of contami-nants or by improper profile height. Each commerciallyavailable primer has a surface preparation recom-mended by its manufacturer. These recommendationsshould be carefully followed.

One of the best ways of minimizing adverseeffects of surface preparation is by careful inspectionof the cleaned surfaces and immediate correction ofany deficiencies found. These deficiencies cannot becorrected after coating application.

The coating manufacturer also provides therecommended ranges of ambient conditions suitablefor successful application of each company product.These recommendations may be as important as anyother manufacturer recommendation.

Inadequate Surface CleanlinessInadequately cleaned surfaces are very

difficult to wet with coatings, because the remainingcontaminants reduce the number of bonding sites.Intimate contact between coating and substrate isnecessary for good adhesion.

Disbonding, Peeling, and Blistering. Disbonding,peeling, and/or blistering may result from incompleteremoval of rust, mill scale, dirt, or other loosely heldcontaminants from the substrate surface or from thepresence of moisture. Flash rusting of properlycleaned steel before coating is another source of thesedefects.

Incomplete removal of contaminants from anexisting coating before topcoating may result inintercoat disbonding, peeling, and/or blistering.

Crawling (Fisheyes). Crawling, sometimes called fisheyes, is the drawing back of a liquid film from a

uniformly thick layer to form areas of little, if any,thickness. It occurs when the surface tension of acoating is greater than the surface tension of thesubstrate. Crawling is caused by substratecontamination with oil or some other low surfaceenergy contaminant.

Figure 18. Crawling (fish eyes).

Figure 19. Osmotic blistering caused by inadequate

removal of soluble salts.

Osmotic Blistering by Incomplete Removal of SolubleSalts. Incomplete removal of soluble salts during

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surface preparation may result in osmotic blistering ofcoatings subsequently applied. These salts are usuallynot readily visible and so must be removed andanalyzed using special techniques.6 The adverseeffects of soluble salts are much greater on coatings inimmersion service than in atmospheric service.

Improper Surface ProfileEach primer has a profile height recom-

mended by its manufacturer for best performance. Anysignificant deviation from this recommendation mayresult in reduced coating system performance. Ingeneral, recommended profile heights vary directlywith the primer film thickness. Thus, primers withgreater film thickness usually have higher recom-mended surface profiles.

Insufficient Profile Height. Insufficient profile height ofcleaned surfaces may provide insufficient bondingareas for adequate coating adhesion. This, in turn,usually results in early coating loss by disbondingand peeling.

Figure 20. Pinpoint rusting.

Excessive Profile Height. Pinpoint rusting may occuron coated steel structures where abrasive blastcleaning has produced so high a profile that it is notadequately protected by a relatively thin primer.Pinpoint rusting may also occur when erosion signifi-cantly reduces coating film thickness.

Coating Defects/Failures from ImproperCoating Application

As with surface preparation, the best way toavoid coating failures resulting from improper coatingapplication is by (1) carefully following the coatingmanufacturer’s recommendations for application and(2) carefully inspecting the work to permit early

detection of defects and their immediate correction. Itis much easier to prevent coating problems associatedwith improper spray application than to correct themafter application.

When applying two-component thermosettingcoatings, careful attention must be paid to themanufacturer’s recommendations for induction, potlife, and recoat times. If this is not done, catastrophicfailure may occur.

Mixing CoatingsAlthough coatings are prepared ready to

apply, settling of the heavier pigment portion mayoccur during storage. Thus, all paints should bethoroughly mixed before application to ensure that thematerial being applied is the homogeneous blendoriginally manufactured. Improper mixing can lead touneven color in cured paint, inadequate film thickness,poor coating adhesion, and checking or cracking of thepaint film.7

Coatings should not be overmixed to avoidentrapping air into them. Thus, a mechanical mixershould be used at a speed set so that a small ratherthan a large vortex or depression on the paint surfaceis created in the center of the can. Use of paint shak-ers is not recommended. Allowing stirred paint to setfor several minutes before application may permit therelease of entrapped air.

Two-component coatings such as thermoset-ting epoxies and polyurethanes are normally suppliedin kits composed of Component A and Component B.The components of each kit must be properly propor-tioned for mixing together to achieve proper curing andoptimum coating performance. Therefore, use ofcomplete kits rather than partially filled kits are recom-mended. Each component should be mixed separatelyand then mixed together in the order specified by thecoating manufacturer.

Plural-component spray application systemscombine Components A and B together automaticallyin a specific ratio. However, the proportions should bechecked before beginning coating application to besure that the proportions are those specified by themanufacturer. When spraying with plural-componentequipment, it is common practice not to use thetriggering technique commonly used with other sprayequipment because the ratio of components may varysignificant at the start and stop of each trigger stroke.Skilled applicators are required for the successful use

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of plural-component application equipment.

ThinningCoatings are manufactured for application as

received without thinning. However, low temperaturesor other conditions may necessitate thinning to reducethe viscosity for effective application. When necessaryto use a thinner, it should be of the type and in theamount recommended by the coating manufacturer.Thinner should be added to the coating slowly andwith thorough mixing to avoid overthinning one portionof the paint and the possibility of curdling the coatingor flocculation of the pigment.

Figure 21. Sagging.

StrainingCoatings should be strained after mixing to

eliminate any skins, lumps, or other foreign matter toavoid clogging spray equipment. Inorganic zinc-richcoatings are especially susceptible to clumping.

Effects of Improper Coating ThicknessIt is important that coatings be applied

uniformly, holiday-free, and in the thickness rangespecified by the manufacturer. Otherwise, maximumcoating performance will not be achieved. Use of a wetfilm thickness gauge, as described in ASTM D 4414,Practice for Measurement of Wet Film Thickness byNotch Gages, will help ensure that the desired dry filmthickness is achieved.

Insufficient Coating Thickness. If a coating is appliedwith less than the specified minimum thickness, itsbarrier protection will be lessened, and thus its servicelife will be reduced. As discussed earlier, a thinner thandesired coating may contribute to pinpoint rusting onsteel surfaces.

Excess Coating Thickness. If a coating is applied toothickly, its weight may cause the wet coating to flowdownward to form sags, runs, or curtains. Suchdefects should be detected and corrected as soon asobserved.

Excessive coating thickness may lead to theacceleration of common cracking, mud cracking, and/or disbondment of relatively rigid coatings. As de-scribed earlier, thicker films have more rigidity thanthinner films and thus are less able to expand andcontract with substrate dimensional changes.

Excess coating thickness may be graduallybuilt up by application of additional coats to an existingcoating system during periodic maintenance painting.When the total stress built up in the coating systemexceeds the adhesion at its weakest point (usuallyprimer to substrate), disbondment will occur.Disbondment may take the form of chipping, flaking,peeling, or delamination.

As described earlier, wrinkling occurs moreoften with thicker than thinner coatings that cure byoxidation of drying oils. Excess thickness may alsoresult in other types of incomplete or improper curing.

Non-Uniform Coating Thickness. If coating thicknessesvary significantly outside the specified range, the firstsigns of deterioration invariably occur in areas of lowfilm thickness. Thus, low thickness areas limit theperformance of the total coated area.

Coatings with variable film thicknesses tend tobe resin-rich in localized areas of greater thickness.This often results in unsightly glossy areas sometimescalled hot spots.

Effects of Improper Spray TechniquesThe most uniform coating application and the

best looking finishes are achieved by spray applica-tion. Deviation from the recommended gun-to-substrate distance, constant rate of gun travel, properspray pattern, and standard triggering can results indefects and early coating failure.

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Figure 22. Dry spray.

Dry Spray. Dry spray is a rough, powdery, non-coherent film produced when an atomized coatingpartially dries before reaching the intended surface sothat the coating cannot flow to form a uniform continu-ous film. This condition most commonly occurs withfast drying coatings. Holding the spray gun too far fromthe substrate may also contribute to dry spray. Dryspray film have little, if any, protective value.

Dry spray should not be confused withoverspray. Overspray consists of atomized paintparticles that deflect from or miss the surface beingsprayed and fall on unintended surfaces.

Pinholing. Pinholing is the formation of small holes thatextend through the entire thickness of a coating. Itoccurs most often with lacquers and other coatingsthat contain fast evaporating solvents. Solvent imbal-ance is an important source of pinholing.

Pinholing is sometimes caused by holding thespray gun too close to the surface with excessiveatomization pressure or a combination of a low atomi-zation pressure and excessive material pressure.

A special case of pinholing often occurs during

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Figure 23. Pinholing.

the topcoating of inorganic zinc-rich coatings on warmdays. Topcoat solvent that enters the naturally porousfilm of the inorganic zinc-rich coating evaporates in thewarm environment, and the resulting vapors rise to thesurface of the uncured topcoat to form pinholes. Thisphenomenon is somewhat similar to outgassing of wetcoatings on concrete, in which, during periods of risingtemperature, interior air and solvent vapors rise to theconcrete surface to form small bubbles in the topcoat.

Cratering is a special form of pinholing causedby foreign matter in or deposited on the wet film.

Coating Holidays. A holiday is a pinhole, skip, disconti-nuity, or void in a coating film that exposes the sub-strate. Unless detected and corrected, holidaysconstitute a source of early electrolyte penetration andcoating deterioration. Holidays in coatings are bestdiscovered using holiday detectors, as described in thechapter of this book on coating inspection.

Topcoating Outside of Recommended RecoatWindow

Manufacturers of two-component thermoset-ting coatings specify a window of time during which

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their coatings can be successfully topcoated. Iftopcoated too soon, the curing of both coats may beadversely affected. If topcoated too late, the topcoatwill have limited adhesion to the undercoat.

Coating Defects/Failures from ImproperCuring

Most coatings require special conditions forproper curing. These include ranges of temperatureand relative humidity. Curing wet coatings at tempera-tures significantly above or below the recommendedrange may result in improper or incomplete curing.

Moisture-curing polyurethanes and alkylsilicate inorganic zinc-rich coatings cure to a solid filmby reaction of their binders with moisture from the air.They must cure within a specific relative humidityrange to achieve complete and proper curing.8 Mois-ture-blushing of coating surfaces during periods ofhigh humidity was discussed earlier in this chapter.

Coatings applied in confined spaces such asstorage tanks may require both heating and ventilatingto remove coating solvents and permit complete curingor curing to the extent required for topcoating. Other-wise, osmotic blistering may be caused by the en-trapped solvent.

SummaryThere are many causes of coating deteriora-

tion. In order to avoid or minimize deterioration, thefollowing actions should be taken:• Proper selection of a high-performance coatingsystem appropriate for the particular environment andservice• Preparation of a job specification that includes allrequirements necessary to achieve long-term coatingperformance• Appropriate surface preparation for the environment,service, and coating system, as recommended by thecoating manufacturer• Appropriate application of the coating system, asrecommended by its manufacturer• Thorough inspection of all phases of the work toensure that all specification requirements are met• Rapid corrective actions to address any deviationsfrom recommendations or early signs of coatingdefects.

References1. Protective Coatings Glossary; Richard W. Drisko,ed; SSPC: Pittsburgh, 2000.2. Drisko, Richard W.; Jenkins, James F. Corrosionand Coatings; SSPC: Pittsburgh, 1998.3. Munger, Charles G.; Drisko, Richard W. A Review ofCommon Failures of Paint Coatings: Part I, DesignFactors. Journal of Protective Coatings and Linings;July 1989, pp 36-41.4. Munger, Charles G.; Drisko, Richard W. A Review ofCommon Failures of Paint Coatings: Part II, Factors ofUncoated and Coated Substrates that Affect CoatingPerformance. Journal of Protective Coatings andLinings; May 1990, pp 62-66.5. The Fundamentals of Cleaning and CoatingConcrete; Randy Nixon and Richard W. Drisko,eds.;SSPC: Pittsburgh, 2001.6. SSPC-TU 4. Field Methods for Retrieval andAnalysis of Soluble Salts on Substrates; SSPC:Pittsburgh.7. Skinner, Jim. Applicator Training Bulletin: Mixing andThinning; Technology Publishing Company: Pittsburgh,1992, pp 65-68.8. Hare, Clive H. Protective Coatings, Fundamentals ofChemistry and Composition; Technology PublishingCompany: Pittsburgh, 1994.

About the Author

Dr. Richard W. DriskoDr. Richard W. Drisko has been the senior technicaladvisor to SSPC: The Society for Protective Coatingssince January 1995. Prior to this, he was employed forover 40 years at the Naval Civil Engineering Labora-tory, Port Hueneme, California, where he conductedresearch, evaluation, and testing, and served as theNavy’s center of expertise on coatings for shorestructures. He is a professional engineer in the state ofCalifornia, an SSPC certified protective coatingsspecialist (PCS), and a NACE International certificatedcorrosion specialist. Dr. Drisko received his BS, MS,and PhD degrees from Stanford.

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