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BUILDING CONSTRUCTION DAMP PROOF COURSE (DPC). DAMPNESS. The access or penetration of moisture content inside a building through its walls, floors, or roof is known as DAMPNESS. SOURCES OF DAMPNESS.
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DAMPNESS The access or penetration of moisture content inside a building through its walls, floors, or roof is known as DAMPNESS.
SOURCES OF DAMPNESS • Damp rising from the soil either through the bottom or through the ground surface, adjacent to the walls. • Moisture penetrating the walls as a result of rain beating on them during continued wet weather. • Moisture penetrating into the building through defective construction, such as rain water pipes, leaking roofs, leaking or choked gutters, etc. • Damp rising from the ground either because there is no damp proof course or because the existing D.P.C. has been bridged by the earth outside, being banked up to form a flower bed or an other purpose.
ILL EFFECTS OF DAMPNESS • It causes rots to the wooden members provided in the building. • It causes corrosion of the metals, used in the construction of a building. • It causes peeling off and removal of plaster. • It causes paints to get blistered and bleached and the surface thus gets disfigured. • It causes floors of the building to remain ugly, since they cannot be cleaned well.
ILL EFFECTS OF DAMPNESS • Carpets if used on the floors of a damped building, gets destroyed earlier. • All electric installations get destroyed. • It reduces the life of the structure as a whole. • When dampness rises into brickwork, certain salts dissolved in it also rise with it and appear in the form of white deposit on the wall surface due to which brickwork disintegrates and falls to powder. • It causes unhygienic conditions for the occupants of the building and affects adversely their health. • Dampness produces unpleasant smell, foul air, mildew fungus, which makes it impossible to store supplies of household goods.
CAUSES OF DAMPNESS • RAIN PENETRATION Properly constructed walls offer considerable resistance to rain penetration but its rapid penetration takes place through the joints and porous bricks or stones. Rain penetration is also possible through the roof components, cracks, and joints b/w the walls and the roof. • LEVEL OF THE SITE Structures built on a higher ground can be drained off easily and hence they are less liable to dampness. But low lying areas cannot be easily drained off and thus causes dampness in the structure.
CAUSES OF DAMPNESS • DRAINABILITY OF THE SITE Gravel and sandy soil allow water to pass through easily whereas clayey soils retain moisture and also causes dampness due to capillary rise. • CLIMATIC CONDITIONS Dampness is also caused due to the condensation of moisture present in the atmosphere under very cold climate. Condensation of the atmospheric moisture can be identified by the drops of moisture present on the ceilings, walls, floors etc.
CAUSES OF DAMPNESS (- ctd -) • DEFECTIVE ORIENTATION The building having its walls subjected to direct showers of rain or getting less direct sun rays, due to defective orientation is liable to dampness. • MOISTURE ENTRAPPED DURING CONSTRUCTION Walls while being constructed are in wet conditions. These may persist moisture for a long period after the construction is over due to the use of salty or alkaline water, which causes dampness in the building. • DEFECTIVE MATERIALS Dampness is also caused due to soakage of moisture by the defective materials like porous bricks, soft stones, etc. especially when they are used in external walls. • DEFECTIVE CONSTRUCTION In case, there is any leakage in the sewers, down water pipes, kitchens, bathrooms, etc., it will be causing dampness in the building.
PREVENTION OF DAMPNESS PRECAUTIONS • Select a sit to make sure that the first point at which water is struck in a pit is at least 10ft below the surface of the ground even in the wet season. • Make the ground surface surrounding the building slope away from the house so that rain water drains away, before it has time to collect. • If the building is on a hill side, make sure that the land above the house is adequately drained around the building and not through it
METHODSThe following are the methods that can be adapted for the prevention of dampness in the buildings: (1) BY SURFACE TREATMENT The surface treatment consists in filling or blinding the pores of the material exposed to moisture by painting a water-repellent material over the surface. Some of the materials employed are: Sodium or potassium silicate, aluminium or zinc sulphates, barium hydroxide and magnesium sulphate in alternate applications, soft soap and alum also in alternate applications, lime and linseed oil, coal-tar, bitumen, waxes and fats, shellacs, resins and gums etc.
(2) BY INTEGRAL TREATMENT • The integral treatment consists in adding certain components to the concrete or mortar during the process of mixing, to make it more dense by filling the pores through chemical action or mechanical effect. • For example, compounds like chalk, talc, fuller’s earth etc. act mechanically and compounds like alkaline silicates, aluminium or zinc sulphates, calcium, aluminium or ammonium chlorides, iron fillings etc. act chemically. • It 5% soap is added in the water to be used for preparing the mortar, the pores get clogged and coating of water repellent substance stick to the wall surface which makes it sufficiently damp proof.
(3) BY SPECIAL CONSTRUCTIONAL TECHNIQUES • By constructing the external walls of sufficient thickness. • By using the bricks of good quality for constructing the external walls. • By building the walls in rich cement mortar. • By providing string courses and cornices. • By fixing down water pipes sufficiently so that water may not leak through the junction of walls and roof. • By constructing hollow brick walls. ( these walls are built, usually with a thick skin of 9in inside, the air space of about 2in between and the outer skin of 4 ½ in. outside. The two skins are boned together by means of galvanized iron wall ties).
(4) BY PROVIDING A DAMP PROOF COURSE The continuous layer of an impervious material, which is provided in between the source of dampness and part of the structure is called a Damp Proof Course.
BY PROVIDING A DAMP PROOF COURSE Damp proof course is of two types: • HORIZONTAL DPC • It is provided in the walls at plinth level in the form of 1 ½ in. thick layer of 1:2:4 cement concrete covered with two coat of hot bitumen or a polythene sheet or metal sheets of lead, copper or aluminum. • It is also provided in the roofs in the form of two coats of hot bitumen, bitumen felt, mastic asphalt or sheets of polythene, lead, copper, or aluminum over the R.C.C. slab. • Horizontal D.P.C. is also provided in floors if the sub-soil water table is high and moisture is likely to rise in the floors by seepage, added by the capillary action of the soil.
BY PROVIDING A DAMP PROOF COURSE (2) VERTICAL DPC • Vertical D.P.C. is mostly provided in the external walls in the form of ¾ in. thick 1:3 cement sand plaster, coated with two washings of hot bitumen. • It is also provided to prevent the dampness into the walls of the basements from the adjacent soils.
D.P.C. IN BASEMENTS (- ctd -) • As basements are built below ground level, these are most likely to be attacked by dampness from the soil below as well as from outside the walls. • A typical basement section showing the damp proof courses is shown in fig-119. • If the head of the water below the level of the floor is high, a layer of gravel 4 ½ in. thick, is laid under the bottom of concrete of floor as shown in fig-120. • Also, gravel is filed between the walls of the basement and adjacent soil.
D.P.C. IN BASEMENTS • The gravel under the floor collects the seepage water and delivers it to the gravel outside the external walls, through the communicating pipes, buried horizontally through the concrete foundation walls. • Drain pipes or footing drains are laid around the footing buried inside the gravel. • These footing drains lead the seepage water to a natural drain, if nearby, or to a dry well. • A dry well is a pit excavated in permeable soil or one having its bottom in such soil and filled with gravel or crushed rock. • If permeable soil is not present nearby, the water is pumped out of dry wells by hand pumps or other techniques.
