Dampproof Materials

7/31/2019 Dampproof Materials

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Water may be present in soils in many forms namely :A. CAPILLARY WATER- water contained in minute pores of

individual soil particles binding them together.B. GRAVITATIONAL WATER: water that flows through the soil and

can be removed by pumping..C. FIM WATER: water surrounding individual soil grains and can

be removed by oven drying.

Ground water level or water table is basically the level of gravitational

water in the soil.

This aspect is best demonstrated by the use of a number of glasstubing of various bores stood upright in a shallow dish of colouredwater.

Water will be found to rise up the tubes of the smallest diameter

tubing.The height to which the water will rise increases as the diameter ofthe tube decreases.

EXPLANATION: reduction in liquid surface area reduces thedownward pull caused by gravity and the upward pull willthereforehave a greater effect.Similarly , capillary rise in soilk depends on the size of pores betweensoil particles.

In sandy soils, pores between grains are relatively large hence verylittle capillarity. In contrast, the capillary rise in fine grained clays isconsiderable . such movement of moisture may also be passed on tobuildings.


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This is basically a surface coating that may be applied by brush,spray or simply bedded in mortar to prevent passage of moisture

especially in situations where there is no hydrostatic pressure fromthe ground.

This is basically the prevention of water that is under pressure byforming a continuous membrane around walls, through concretefootings and / or within concrete floor slabs.

1. Hydrostatic pressure forces water into pores of masonry orconcrete surfaces where it can chemically attack cementitiousmaterials forcing them to deteriorate.

2. reinforcements corrode in the presence of moisture.3. entrapped water can freeze causing cracks4.

fungi growth leads to dry and wet rot.5. adhesion of plaster work and paints will be greatly be affected.6. mould growth and condensation will result in staining of walls.7. pungent smells from condensation, mould growth and rotting

timber creates an unhealthy environment.8. paints will bleach as a result of moisture9. efflorescence develops on brickwork and plaster .

Basically moisture gets into a structure from the TOP, SIDES ANDFROM THE GROUND (capillary action or hydrostatic pressure).


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- -suitable for stepped damp proof courses but tends to corrodewhen it gets in contact with fresh lime mortar.

B. copper: does not extrude under pressure, highly resistant tocorrosion but is known to stain external surfaces of brickwork

or stone work.C. Bitumen felt/ malthoid: flexible and impervious moisture .withstands distortion due to average settlementobtained in various bases such as FIBRE; ASBESTOS; HESSIAN.bitumen is distilled from petroleum and can be impregnated in a

fibrous base to form bitumen felt.d. polythene-0.5mm: flexible and impervious to moisture and hasa moderate resistance to sliding.- should be laid on an even bed of mortar

-has a high chemical resistance.E. mastic asphalt: a semi rigid damp proof material applied in itsmolten state to a 13mm thick layer. Liable to extrude underpressure.

Bricks: engineering bricks

2 courses laid in 1:3 cement mortar

SlatesAt least 230mm long and not less than 4mm thick.2 courses laid in 1:3 cement mortar

Factors to consider when selecting an appropriate dpm1. position on the building2. design of the structure

3. total loading on the dpc4. cost considerations5. other building materials


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Dampproof Materials