Materials Used For Damp Proofing (DPC) | What Are The Materials Used For DPC? (2024)

MATERIALS USED FOR DAMP PROOFING (DPC)

There are various materials, which are used as damp-proofcourses depending upon the location, economy and degree of damp proofing desired.However, while selecting a particular damp-proofing material, the followingrequirements of an ideal damp-proofing material should be remembered.

1. Thematerial for DPC should be impervious and durable, i.e., the material should beeffective during the useful life of the building.

2. Thematerial should be capable of resisting both dead loads and superimposed loadswithout being disintegrated.

3. Thematerial should remain steady in its position, without any movements, so thatthe walls overlying the DPC do not develop any cracks.

4. ForDPC above the ground level, with wall thickness up to 40 cm, any materiallisted below for DPC can be used.

5. ForDPC to be laid over larger areas, such as floors and roofs, and thicker walls, aDPC material that provides a lesser number of joints should be used, such asmastic asphalt, bitumen sheeting and plastic sheeting.

6. Thematerial for parapet walls and in other situations where differential thermalmovements are expected due to exposure should be of flexible material, likemastic asphalt, bituminous felt and metal sheets.

7. Inwater-retaining structures or situations, a jointless DPC should be provided totake care of the risk of leakage.

8. In the cavity or hollow walls, the cavity over the door or window openings should bebridged by flexible materials, like bitumen sheets, strips of lead and copper.

Thematerials generally used for DPC are listed below.

1. Flexiblematerials: Hot bitumen, bituminous felts, bituminous sheet, plasticsheet (polythene sheets), metal sheets of lead, copper, etc.

2. Semi-rigidmaterials: Mastic asphalt or a combination of materials or layers.

3. Rigidmaterials: Use of I-class bricks, stones, slates, etc.

Hot bitumen or hot asphalt

This is a flexible material, which is first heated and thenspread over the bedding of concrete or mortar (i.e., over walls). This shouldnot be applied in thickness less than 3 mm. Bitumen or asphalt forms anexcellent damp-proof course, as it offers an impervious, indestructible andtough surface.

Bituminous felts (6 mm thick sheet or asphaltic felt)

This is also a flexiblematerial, which is available in rolls of normal wall widths. For placing thisin position, first a layer of cement mortar is laid on the brickwork and thenDPC is bedded on it. An overlap of 10 cm in case of joints and full-widthoverlap in case of angles and crossings should be provided. Bitumen felt iscapable of accommodating slight movements but cannot withstand heavy loads.

Sheets of lead, copper and aluminium (metal sheets)

These are used as membranes for damp proofing and are offlexible type.

Sheets of lead

The thickness of the sheet shouldbe such that the weight of the sheet is not less than 20 kg/m2. These are spread onthe walls and overlapped at the joints. The sheets of lead should be embeddedin lime mortar and not in cement mortar (because cement chemically reacts withlead and destroys it). The surfaces of lead should be protected by a coating ofbitumen against corrosion. DPC formed by lead sheet provides an impervious andhighly resistant surface against lateral movements.

Sheets of copper (minimum 3 mm thick)

Like lead sheets, these arespread, lapped and jointed. They are embedded in lime or cement mortar. This isanother excellent DPC material that possesses characteristics such as highdurability, good resistance to dampness and high resistance against slidingaction.

Sheets of aluminium

These can also be used for DPC but not as good as to lead orcopper sheets. These sheets should be protected with a layer of bitumen.

Combination of sheets and bituminous felts

A lead foil is sandwiched between the sheets of asphalt orbituminous felt. This combined sheet is known as ‘lead core’ and DPC of thiscore possesses the characteristics of easy laying, durability, efficiency andeconomy.

Mastic asphalt

This is obtained by heating the asphalt with sand andmineral fillers. This is a semi-rigid material and forms an excellent imperviouslayer for damp proofing, i.e., DPC. However, it requires special care in itslaying. Good mastic asphalt has many characteristics, such as high durability,excellent water-proofing quality and reasonable elasticity. This can withstandonly very slight distortion and is liable to lateral movements under heavypressures or very hot climates.

ALSO READ: DampProofing | Sources Of Dampness | Effects Of Dampness | Techniques And Methods |Uses

Bricks

Good dense bricks, which absorb water less than 4 per centof their weight, are suitable as a DPC material at places where the damp is notexcessive. The joints are left open. They are widely used for providing orinserting a DPC membrane in an existing wall.

Stones

Generally, dense and sound stones, such as granite, trapand slates, are laid in cement mortar in two courses to form an effective DPC.The stones are used for the full width of the wall. While laying the stones,care should be taken in breaking the continuity of vertical joints.

Cement concrete layers

A cement concrete layer,having mixed proportions 1:2:4 (1 cement:2 sand:4 aggregates) with waterproofingagents, is used as DPC at the plinth level. It is effective in stopping thewater rising due to capillary action but allows the water to pass through thecracks, etc., and hence is suitable as DPC material where dampness is not inexcess. The concrete layer is used as a horizontal main DPC in thickness varyingfrom 4 to 15 cm followed by two coats of hot bitumen paint.

Mortar

It is used in two ways, either(i) as a bedding layer for taking up other types of DPC or (ii) as awaterproofing plaster. For the bedding layer, the mortar is prepared by mixingcement and sand in proportions 1:3 and adding slight lime to increase theworkability. For waterproofing plasterwork, the mortar is prepared by mixingeither of the following:

a. 1 cement:2 sand pulverized alum andsoap water,

b. Cement: sand in proportions 1:3, with patented waterproofingmaterial like pudio, dampro and sika. After applying this plaster in 2–4 cmthickness, it is painted with two coats of hot bitumen.

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