Damp Proof: Treatment, Cure and Prevention
Damp proofing is defined by the American Society for Testing and Materials (ASTM) as a material that resists the passage of water with no hydro-static pressure and waterproof as a treatment that resists the passage of water under pressure. Generally damp proofing keeps moisture out of a building where vapor barriers keep interior moisture from getting into walls. Moisture resistance is not necessarily absolute: it is usually defined by a specific test method, limits, and engineering tolerances.
1. METHODS OF DAMP PROOFING
1.1 Integral damp proofing
– Integral damp proofing in concrete involves adding materials to the concrete mix to make the concrete itself impermeable.
– This consists of adding certain water proofing compounds with the concrete mix to increase its permeability. These compounds are available in liquid or powdered form.
– The compounds like alkaline silicates, aluminium-sulphates, calcium chlorides, react chemically, when mixed in concrete to produce water proof concrete.
1.2 Surface treatment
This treatment consists of filling up the pores of the surfaces through which moisture enters.
The use of water repellent metallic soaps, such as calcium and aluminum oleates is much effective in protecting the building against the heavy rain. In addition to these, the cement lime plaster (1:1:6) is done to prevent the dampness in the walls due to rain.
1.3 Cavity wall construction
This is an effective method of damp prevention, in which the main wall of the building is shielded by an outer skin wall leaving a cavity in between the two. Cavity wall construction such as rain screen, construction, is where the interior walls are separated from the exterior walls by a cavity.
This treatment consists of depositing an impervious layer of rich cement mortar over the surface to be water proofed. The cement mortar (1:3) to (1:4) is shot on the prepared surface under a pressure of 2 to 3 kg/cm². The nozzle of the cement gun is kept at s distance of 75 to 90 cm. from the working face. The treated surface ids then cured for at least 10 days.
1.5 Pressure grouting
This consists of forcing the cement grout, under pressure, into the cracks, voids, fissures, etc. present in the structural components of the building or in the ground. This method is quite effective in checking the seepage of raised ground water through foundations and sub-structure of a building.
2. MATERIALS USED FOR DAMP PROOFING
Materials widely used for damp proofing include;
– Flexible materials like butyl rubber, hot bitumen, plastic sheets, bituminous felts, sheets of lead, copper, etc.
– Semi-rigid materials like mastic asphalt
– Rigid materials like impervious bricks, stones, slates, cement mortar or cement concrete painted with bitumen, etc.
– Mortar with waterproofing compounds
– Coarse sand layers under floors
– Continuous plastic sheets under floors
3. DAMP-PROOFING TREATMENT IN BUILDINGS
3.1 Treatment to foundations on ordinary soil
In case of building foundations on ordinary soil, where the subsoil water table is not high, brick masonary below ground level can absorb moisture from adjacent ground make the wall damp by capillary action. This can be prevented by providing DPC, at least 150mm above ground level or plinth level.
3.2 Treatment of foundations on damp soil
In case of building constructed on damp soil in wet areas, the wall as well as the ground floor is liable to become damp due to capillary rise of moisture from ground. In such case the DPC, is laid over the entire ground floor area including wall thickness.
3.3 Treatment to basements in ordinary soil
In case where the subsoil water table is low, & there is no water pressure, a horizontal DPC over the entire area of floor & vertical DPC on external faces of the basement walls is provided as follows;
– Apply hot bitumen at the rate of 1.5kg/m² over the prepared surface as primer coat
– Lay bitumen felt in single layer over primer coat.
3.4 Treatment to basement in damp soil
In case where the ground water table is high, the PDC of basement is provided in three ways;
– Provision of foundation, drains &DPC.
– Provision of RCC raft & wall slab & DPC.
– Water proofing treatment by using grout consisting of mortar admixed with acrylic based chemicals along with stone slabs.
3.5 Treatment to floors
– The stone soling laying is provided & rammed properly.
– The floor topping comprise of tiles, stones & cement concrete is provided.
3.6 Treatment to walls
– The moisture may enter from the external face to the internal face of the wall due to the porosity of bricks & mortar joints.
– The various treatments can be given to the exposed surface of the wall, to prevent dampness include plastering, pointing &painting etc.
– The plaster made out of cement lime & sand mixed in proportion of 1:1:6 mat be very effective to protect the walls against dampness in normal weather conditions.