If yo u’re like most tilt-up con-t ra c t o r s, you probably don’tseal tilt-up panel joints yo u r-self. By the time the joints are

ready to caulk, yo u’re busy on an-other tilt-up job. So how do yo ue n s u re that the subcontractor yo uh i re does the job right? He re areten tips.

1 . Speci f y t he r i ghtseal ant .

Si l i c o n e s, polysulfides, andp o l y u rethanes have all been usedto seal concrete tilt-up panels.These thermosetting, chemicalc u ring sealants resist we a t h e ri n g ,u l t raviolet radiation, and ozo n e.T h e y ’re flexible and resilient atboth high and low tempera t u re s,and they’re inert to a wide range ofc h e m i c a l s.

Silicone sealants can tolera t e

much greater movements thanpolysulfides or polyure t h a n e s :+100% and -50%, compared with±25% for most polysulfides andp o l y u re t h a n e s. They maintain thisflexibility over a wider tempera t u rerange than polyurethanes or poly-s u l f i d e s, and they also resist sol-ve n t s, fuels, and oxidizing agentsb e t t e r.

Howe ve r, silicones do not re s i s talkalies well. And compared top o l y u re t h a n e s, they don’t adhere aswell to concrete without a pri m e r,they can’t be color-matched to con-c rete as well, they can’t be painted,and they pick up more dirt. Theyalso cost more.

For best results at an economicalp ri c e, specify a polyure t h a n esealant that meets the re q u i re-ments of Re f e rence 1 for:• Type S (single-component) or

Type M (multicomponent)• Grade NS (nonsagging when ap-

plied between 40°F and 122°F)• Class 25 (withstands 25% in-

c rease and decrease in jointwidth)

Sh o p a ro u n d . So m e p o l y u re t h a n e sa re a va i l a b l e t h a t e xc e e d C l a s s 2 5re q u i re m e n t s. On e p ro p ri e t a ryp ro d u c t c a n t a k e m ove m e n t s o f± 5 0 % .

Though polysulfides are stillused and still acceptable,p o l y u rethanes have been re p l a c i n gthem over the last 15 to 20 ye a r s.

“Po l y u rethane is the material ofm y c h o i c e,” says Joe Na r by, genera lm a n a g e r, construction, Ha s k e l lCo., Ja c k s o n v i l l e, Fla. “It holds upb e t t e r, cures better, and stands upto weather and movement betterthan polysulfide.” Haskell buildsh u n d reds of thousands of square

Sealing Joints InTi l t - Up Pa n e l s

BY MARK A. WALLACE

Ten ways for tilt-up contractors tomake sure that joints betweenpanels get properly sealed

feet in tilt-up each ye a r.Ma rk Beamish Wa t e r p ro o f i n g

In c., Anaheim, Calif., switchedf rom using polysulfides top o l y u rethanes about five years agobecause polyurethanes cost less:$30 a gallon compared with $33 to$34 a gallon for polysulfides. Own-er Ma rk Beamish, who annuallyinstalls more than $2 millionw o rth of caulking in tilt-up panelj o i n t s, also found that polysulfidestended to wrinkle because of theirs l ower cure.

“In Las Vegas and Re n o, wherewe do some work ,” says Be a m i s h ,“tilt-up joints can open from 1⁄4 to 1⁄2inch in one day, as the tempera t u regoes from hot to cold. Po l y s u l f i d esealant would wrinkle as the panelsm ove d .”

2 . On i nt er i or j oi nt s,use an acr yl i c seal ant .

To economize without sacri f i c i n gp e rf o rm a n c e, many specifiers arecalling for acrylic sealants on thei n t e rior of tilt-up joints. At $12 to$15 a gallon, acrylics cost abouthalf as much as polyure t h a n e s. Un-like polyure t h a n e s, they can bepainted within hours.

Since acrylics don’t tolerate asmuch movement (usually only ±7%to ±12.5%) as polyurethanes do, usea c rylics only on the interior andp o l y u rethane sealants on the exte-rior of the joints. Be aware thata c rylics va ry in price and quality.Some cost 75¢ a cart ridge; othersrun $3 a cart ri d g e. Mo re expensivep roducts generally have morem ovement capability.

3 . For f ast est cur e,choose a t w o- par tseal ant .

Field-molded sealants usuallycome in one or more part s. On e -p a rt sealants cure as they pick upm o i s t u re from the air, so they’rem o re dependent on enviro n m e n t a lconditions (mainly tempera t u reand humidity) than multiparts e a l a n t s. Commonly used two-partsealants cure chemically once thep a rts are mixed together. Thus, theirc u re is less affected by we a t h e r.

Many applicators prefer two-p a rt sealants because they comein bulk, are slightly cheaper, andc u re quickly. Though mixing isnot difficult, it must be donep ro p e r l y, or the sealant may notc u re at all.

“It stays gooey,” says Na r by. “Itgets a surface crazing, and whenyou touch it, you get bubble gum. Itstays like that fore ve r.”

Properly mixed and cure dsealant behaves like a pencil era s-e r. You can push your fingernail in-to it or cut it with a ra zor knife.

Despite the extra labor that mix-ing re q u i re s, Na r by prefers using at w o - p a rt sealant. A two-partp o l y u rethane that’s applied in them o rning can cure by the aftern o o n ,he says, creating less worry aboutunexpected rain. Cu ring so quickly,the two-part polyurethane alsopicks up less dirt. In contrast, ao n e - p a rt polyurethane stays tackyl o n g e r, and wind can then coat itwith a disfiguring layer of dust.

Beamish, on the other hand, at-t ributes his company’s success, inp a rt, to the efficiency of one-parts e a l a n t s. “For a 100,000-square -foot tilt-up warehouse building,we’ll bring out five or six work e r sand do the job in one day. We pur-chase sealant in 5-gallon bucketsand suck the sealant out of thebucket directly into the [caulking]gun. We like the one-part sealantbecause it’s fast.”

4 . Use seal ant s t hat donot r equi r e pr i mer s.

Ac c o rding to Re f e rence 2, ther-mosetting, chemical curi n gsealants such as polysulfides,p o l y u re t h a n e s, and silicones g e n -e ra l l y re q u i re a primer if they areto adhere satisfactorily to con-c re t e. Ma n u f a c t u rers of theses e a l a n t s, howe ve r, usually re q u i rea primer only on certain finishes,under seve re conditions, or injoints that can’t be cleaned ade-q u a t e l y. Primers can fill pore s,s t rengthen the substra t e, and im-p rove adhesion.

When conditions warrant theuse of pri m e r s, manufacturer re c-

ommendations should be fol-lowed. Primer, for example, shouldbe applied uniform l y, any exc e s sshould be re m oved, and the coatshould be allowed to dry beforesealant is applied.

If possible, though, choose asealant that doesn’t re q u i re ap rimer on new tilt-up panels(many polyurethanes don’t). Se a l-ing contractors don’t like using ap ri m e r. It adds work and materi a lcost. Mo re ove r, if too much pri m e ris used or if it doesn’t dry complete-ly before caulking, the primer itselfcan cause pro b l e m s.

5 . Cont r ol seal antdept h.

Keeping the depth of sealant thinin relation to the joint width con-s e rves material and improves per-f o rm a n c e. So check that the caulk-ing contractor always installs thep roper size backer rod to thesealant manufacture r’s re c o m-mended depth. In general, for tilt-up joints, which usually are 1⁄2 to 3⁄4inch wide, sealant depth should beone-half the joint width and neve rm o re than 1⁄2 i n c h .

If the backer rod is placed tood e e p, the sealant gets applied toothick and can’t stretch enoughwhen the concrete panels contra c tin cold we a t h e r. The result: adhe-s i ve failure as the sealant pulls offthe sidewalls of the joint.

If the backer rod is placed toos h a l l ow, not enough sealant gets

Generally, sealant depth should beone-half the joint width and nevermore than 1⁄2 inch.

injected into the joint. The re s u l t :c o h e s i ve failure. Applied too thin,the sealant tears when the tilt-uppanels move. Even when thebacker rod is installed at thep roper depth, this problem canoccur if the caulker fails to injectenough sealant.

Beamish says you can tell whenthe joint doesn’t contain enoughsealant. “When you press on thesealant, it feels spongy. You can feelthe foam backer rod close by un-d e rneath. It’s almost as if thesealant was painted on.”

When you press on the sealantwithout making much of a dent,you know that enough sealant wasa p p l i e d .

Closed- or open-cell polye t h y l-ene or polyurethane foam can beused as backer rod. (Don’t use ma-t e rials containing bitumen orvolatile materials; these may im-pair adhesion.) To keep the backerrod from falling out or gettingpushed further into the joint, use arod that is larger in diameter thanthe joint is wide. Ac c o rding to Re f-e rence 3, rod diameter should ex-ceed joint width by 25% to 33% forclosed-cell rods and 40% to 50% foropen-cell ro d s.

In all cases, the sealant shouldnot adhere to the backer rod, a con-dition called three-sided adhesion.If it does, the sealant won’t be fre eto extend and compress as the tilt-up panels contract and expand.

6 . Make sur e t he j oi nt sget cl eaned w el l .

Sealant won’t bond to concrete ifthe concrete is not clean. Jo i n t smust be free of moisture, fro s t ,dust, sealers, form release agentsand, as Na r by puts it, “w h a t e ver goton the panels while they we re lyingon the gro u n d .”

After wire brushing the joints,Na r by has his workers wrap a ra ga round the wire brush and wipe thejoints clean. Be a m i s h’s crew wipesout the joints with a rag and some-times with a piece of backer rod.

W h a t e ver you do, don’t let thesealing contractor use solvents toclean the concre t e. So l vents in-

tended to re m ove oil can carry thecontaminants deeper into the con-c rete instead.

The joints are clean if no dust orlaitance comes off on the hand. Yo ucan also check for laitance by ap-plying masking tape, then lookingfor any white powder on the tapeafter stripping it off (Ref. 4).

Many bond breakers and formrelease agents used today dissipatewith time. These materi a l s, howe v-e r, can still pre vent sealants fro ma d h e ring to concrete if the jointsa re caulked before they dissipate.To avoid this problem, check thedissipation time of the bond bre a k-er or form release agent and makes u re that the caulking contra c t o rwaits this long to caulk joints. Also,be sure a dissipating bond bre a k e ri s, in fact, being used. So m enondissipating form release agentsa re still in use today.

7 . Pr ohi bi t seal i ng i ncol d or w et w eat her .

In cold we a t h e r, the surface we t-ting chara c t e ristic of a sealant is re-duced, some sealants don’t flow aswell, and frost or ice in the jointmay inhibit adhesion. Thus, it’sbest to apply sealants at tempera-t u res above 40°F.

Hot weather generally poses nop ro b l e m s, though it may accelera t ec u re and thus reduce pot life, tool-ing time, and tack-free time. How-e ve r, if joints are sealed in thehottest part of the ye a r, the sealantwill experience a lot of move m e n twhen cold weather comes and thetilt-up panels contract. To mini-m i ze the amount of this move-ment, it’s best to apply sealants att e m p e ra t u res below 90°F. In fact,the closer the tempera t u re at in-stallation is to the mean annualt e m p e ra t u re, the less strain on thesealant there will be.

“If yo u’re going to have a sealantf a i l u re, it commonly will occur dur-ing the first season change,” saysNa r by. That’s when both the panelsand sealant experience the mostm ove m e n t .

Tilt-up panels also can’t be we twhen they are sealed. Si n c e

p o l y u rethane and most othersealants don’t stick well to wet sur-f a c e s, have the caulking contra c t o rwait a day or two after a rain beforesealing, or make sure the panels aresufficiently dry.

D o n’t allow caulking too soon af-ter the panels are cast, or the con-c rete may be too wet. Wait at least28 days after casting before sealing.In cold we a t h e r, wait even longer,maybe 40 days. To be sure that thepanels are dry enough, check thepH of the concre t e. It should be be-t ween 7.2 and 7.4, compared with 9for green concre t e. In warm we a t h-e r, the pH of concrete is in this ac-ceptable range after one month ofc u ri n g .

8 . Make sur e t he j oi nt sget t ool ed.

Immediately after the sealant isapplied, joints should be tooled.Tooling with a concave tool thatlooks like a brick mason’s jointerf o rces the sealant into contact withthe sides of the joint. It also helpseliminate air pockets and cre a t e san hourglass cross section thatplaces the maximum stress in themiddle of the sealant rather than atthe joint sidewalls, where it couldcause adhesive failure.

To keep the tool from sticking tothe sealant, rinse it regularly ins o a py water. Don’t use oils, alco-h o l s, or solve n t s. They may conta-minate unsealed joints or discolorthe surf a c e.

Caulkers must learn how to usethe tool. If they push too hard ,sealant slops out and creates amessy job. Excess sealant andsmears should be re m oved imme-d i a t e l y. Wo rkers should scra p e,w i p e, or scrub the spill with drytools or ra g s. Again, don’t use sol-ve n t s, as they may dri ve the sealantdeeper into the concre t e, leaving ap e rmanent stain.

9 . I nspect t he w or k.No standard field test has been

d e veloped for checking the adhe-sion of joint sealants. But there areways a tilt-up contractor or build-ing owner can make sure the seal-

ing was done well. To check sealant depth, poke the

sealant with a pencil while the ma-t e rial is still soft. Then have thecaulker re-tool over the pencil hole.One or two weeks after the caulkersh a ve completed their work, have afield foreman check bond at ra n-dom spots and re c o rd the re s u l t s.

With a blunt end of a pocketk n i f e, pencil, or trowel, probe thesealant and see if it pops off. If yo uc a n’t induce failure in this way,sealant adhesion is probably good.Or try a pull test: Cut the sealantalong one edge of the joint, thent ry to pull the sealant out of thejoint. If you can pull sealant awayf rom the opposite joint face,sealant adhesion is inadequate.

It’s best to also perf o rm thesetests on mock-up panels before thejob begins to make sure materi a l sand application techniques are ap-p ro p ri a t e.

1 0 . Choose a qual i t ycaul ki ng cont r act or .

“Caulking needs to be done by ap rofessional waterpro o f e r,” Na r byc l a i m s. “Most painting contra c t o r sa re n’t equipped to do caulking andd o n’t have trained people.”

If you don’t seal the joints yo u r-self, hire a contractor with experi-ence in caulking, pre f e rably one

like Beamish, who specializes incaulking tilt-up. Check if the con-t ractor warranties its work (somere p o rtedly give five - year war-ranties). And always check re f e r-e n c e s.

Fo l l ow these ten tips, and thejoint sealants on your tilt-up workp robably will last 10 to 12 ye a r s,possibly longer. Ig n o re them, andthe sealants may fail during thefirst change of seasons.

References1. Standard Specification for Elas-tomeric Joint Sealants, ASTM C 920-95, ASTM, West Conshohocken, Pa.,1987.

2. ACI Committee 504, Guide to Seal-ing Joints in Concrete Structures, ACI504R-90, American Concrete Insti-tute, Farmington Hills, Mich., 1990.3. Standard Guide for Use of JointSealants, ASTM C 1193-91, ASTM,1991.4. Hugh Brooks, The TILT-UP Designand Construction Manual, 3rd ed.,HBA Publications, Newport Beach,Calif., 1994.

Mark A. Wallace is a fre e l a n c ewriter based in Oak Park, Ill. Hespent several years on the editorials t a ff of C o n c rete Constru c t i o n a n dis a former editor of A b e rd e e n ’sMagazine of Masonry Construction

To check sealant depth,poke the sealant with apencil while the materialis still soft. Then havethe caulker re-tool overthe pencil hole.

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