Damp Proofing

NATIONAL INSTITUTE OF TECHNOLOGY, WARANGAL

ASSIGNMENT ON

DAMP PROOFING IN MASONRY CONSTRUCTION

SUBMITTED TO Prof. D. RAMASESHU Dept. of Civil Engg. 09108)

SUBMITTED BY Y. KARTHEEK (CE 09207) G. V. RAVIKIRAN (CE

CONTENTS 1. Introduction 2. Sources (or causes) of Dampness 3. Effects of Dampness 4. Techniques and Methods of Damp Prevention 5. Damp-proofing(i.e., D.P.C) Treatment in Buildings

DAMP PROOFING: Damp proofing is the chief requirement to ensure the safety of buildings against dampness. The entry of water in different components of a buildings such as walls, roofs, parapets , etc.., can be done by the way of damp proofing materials and techniques which is termed as damp proofing or damp prevention. The various materials that are used for the damp proofing are bitumen sheets, plastic sheets, mastic asphalt, bricks, stones, cement concrete, slates are applied in courses (known as damp proof courses) at appropriate positions in the building. Techniques such as guniting, cavity wall construction, etc…, are also adopted for damp proofing of buildings. SOURCES OR CAUSES OF DAMPNESS: Dampness in buildings is generally because of the following reasons: 1. Faulty design of structure. 2. Faulty construction or poor workmanship and 3. Use of poor quality materials in construction. The various sources which create dampness in buildings are as follows: 1. RISING OF MOISTURE FROM THE GROUND: The sub-soil or ground on which the building is constructed may be made of soils which easily give an access to water to create dampness in buildings, through the foundations. 2. ACTION OF RAIN WATER: Whenever the faces of walls are not suitably protected from the exposure to heavy showers of rains, they become the sources of dampness in a structure. 3. RAIN PENETRATION FROM TOPS OF WALLS: All parapet walls and compound walls of the building, which have not been protected from rain penetration by using damp proof course or by such measures on their exposed tops, are subjected to dampness. This dampness in buildings of serious nature and may result in unhealthy living conditions are even in structurally unsafe conditions. 4. CONDENSATION DUE TO ATMOSPHERIC MOISTURE: Whenever the warm air in the atmosphere is cooled, it gives rise to the process of condensation. On account of the condensation, the moisture is deposited on the whole area of walls, floors, and ceilings. 5. MISCELLENEOUS SOURCES OR CAUSES:

The various other sources or causes which may be responsible for dampness in buildings are mentioned below: a. Poor drainage on the site. b. Imperfect orientation. c. Constructional dampness. d. Dampness due to defective construction. EFFECTS OF DAMPNESS: The various effects caused due to dampness in buildings are: A damp building creates un healthy living and working conditions for the occupants. 1. It may result in softening and crumbling of plaster. 2. Presence of damp conditions result in the disintegration of bricks, stones, tiles etc.., and hence in the reduction of strength. 3. It may cause flaking of the paint which results in formation of the coloured patches on the wall surfaces and ceilings. 4. It may result in corrosion of metals used in the construction. 5. Dampness promotes the growth of termites and hence creates unhygienic conditions in buildings. All these effects mainly result in poor functional performance, ugly appearance and structural weakness of the buildings. PRECAUTIONS TO PREVENT DAMPNESS: 1. The site should be located on a high ground and well drained soil to safe guard against foundation dampness. 2. All the exposed walls should be of sufficient thickness to safe guard against rain penetration. 3. Bricks of superior quality, which are free from defects such as cracks, flaws, lump of lime stones etc.., should be used. 4. Good quality cement mortar (1 cement: 3 sand) should be used to produce a definite pattern and perfect bond in building units throughout the construction work. 5. Cornices and strings courses should be provided. 6. All the exposed surfaces like tops of walls, compound walls, etc.., should be covered with water proofing cement plaster. 7. Hollow walls are more reliable than solid walls in preventing dampness and hence the cavity wall construction should be adopted where ever possible.

PREVENTION OF DAMPNESS:

The various techniques and methods generally adopted to prevent the defects of dampness are as follows: 1. 2. 3. 4.

Use of damp proofing courses or damp proofing membranes. Water proof or damp proof surface treatments. Integral damp proofing treatments. Cavity walls or hollow walls. 5. Guniting or shot concrete and 6. Pressure grouting or cementation. 1. USE OF DAMP PROOFING COURSES: These are the layers or membranes of water repellent materials, such as bituminous felts, mastic asphalts, plastic sheets, cement concrete, mortar, stones etc.., D.P.C. is provided to prevent the water rising from the sub-soil or ground and getting into the different parts of the building. The best location or position of the D.P.C in case of buildings without basements lies at the plinth level or in case of structures without plinth it should be laid at least 15cms above the ground level. These D.P.C’S may be provided horizontally or vertically in floors, walls etc.., 2. WATER PROOF (OR DAMP PROOF) SURFACE TREATMENTS: The surface treatment consists in filling up the pores of the material exposed to moisture by providing a thin film of water repellent material over the surface. Many surface treatments like pointing, plastering, painting, distempering, are given to the exposed surfaces and also to the internal surfaces. The most commonly use treatment to protect the walls against dampness is lime cement plaster of mix (1 cement: 1 lime: 6 sand) proportions. A thin film of water proofing materials can be applied to the surface of concrete after it is laid. 3. INTEGRAL DAMP PROOFING TREATMENT: The integral treatment consists adding certain compounds to the concrete or mortar during the process of mixing, which when used in construction, acts as barriers to moisture penetration. Compounds like chalk, talc, fuller’s earth fill the pores result in the concrete or mortar and make them denser and waterproof. The compounds like alkaline, silicates, aluminium sulphates etc.., react chemically and act as water resistant. The synthetic compounds available in commercial forms like pudlo, sika, dampro, permo raines can also be used.

4.

CAVITY WALLS OR HOLLOW WALLS: Cavity wall consists of two parallel walls or skins of masonry separated by a continuous air space or cavity. Cavity walls consists of three main parts namely, the outer wall or

leaf (10 cm thick) which is the exterior part of the wall, the cavity or air space of 5cms to 8cms and the inner wall or leaf which is the interior part of the wall. The provision of continuous cavity in the wall efficiently prevents the transmission or percolation of dampness from outer wall to the inner wall. Under climatic conditions of India this cavity type of construction is most desirable as it offers many advantages such as better living and comfort conditions, preservation of the building against dampness. The cavity wall construction offers the following advantages over solid wall construction: a. As there is no contact between outer and inner walls of a cavity wall the moisture penetration is reduced to a minimum. b. As air in the cavity is non conductor of heat, so it prevents the transmission of heat through the walls and maintains better consistency of temperature inside the building. c. The cavity walls offers good insulation against sound. d. The cavity tends to reduce the nuisance of efflorescence. e. This type of construction also offers many other benefits such as economy, better comfort and hygienic conditions in buildings. 1. GUNITING(OR SHOT CONCRETE) This is a technique of forcing or ejecting through a cement gun an intimate mixture of cement, sand (or fine aggregate) and water and applying shot into place by means of compressed air. The cement mortar so applied to exposed concrete surfaces acts as a waterproofing course. This technique is also applied for re conditioning old concrete, brick or masonry walls which are deteriorated either due to climatic effects or bad workmanship.

2. PRESSURE GROUTING(OR CEMENTATION): Cementation is the process or technique of forcing the cement grout (i.e., mixture of cement, sand and water) under pressure into the cracks. Voids or fissures present in structural components of a structure in general and foundations in particular, which are liable to moisture penetration, are consolidated and hence made water-resistant by this concentration process.

DAMP-PROOFING (i.e., D.P.C) TREATMENTS IN BUILDINGS The use of damp-proofing courses for the treatment of buildings, against dampness, can be grouped into the following categories:

1. Treatment of foundations dampness from adjacent ground 2. Treatment of foundations on bad (poor) soils. 3. Treatment of basement. 4. Treatment of floors. 5. Treatment of walls. 6. Treatment of flat roofs, parapets and copings. 7. Treatment of pitched roofs. 1. TREATMENT OF FOUNDATIONS DAMPNESS FROM ADJACENT GROUND: In case the moisture rises up the walls through the foundations where water is percolating from the adjacent ground, this may be treated by providing air drains and damp-proof course or by D.P.C. alone. Sub-soil drainage may also be provided to solve this problem. An air drain is a narrow dry space (20 to 30 cm width) which is provided on the outer face of the wall below the ground level. It is formed by a thin outer wall resting on the base slab of foundation and carried little above the ground level to prevent water entering the drain. 2. TREATMENT OF FOUNDATIONS ON BAD (POOR) SOILS: Where the foundations of basements are not properly drained and subjected to great hydrostatic pressure, then in such cases the structure should be disconnected from the face of the ground excavation and a trench made all around for width of about 30 cm taken down to a point as low as under side of the concrete footings. This becomes essential, because the provision of continuous D.P.C. may not give satisfactory results. The bed of the trench should be provided with a good slope at each end and the trench filled with coke, gravel, or stone graded with fines to fill the voids. In this case the basement is relieved of hydrostatic pressure by suitably draining the sub-soil water. Subsoil water may be drained by providing open jointed land drain at the bottom of trench and also drainage-pipes below the concrete base.

D.P.C. treatment of foundation on bad soils

3. TREATMENT OF BASEMENTS: To ensure the dryness, the whole of the structure below ground level should be provided with a continuous membrane of asphalt or bituminous felt supported on the inside. This can be achieved by spreading a layer of an impervious material over the whole area of the floor and continuing the same through the external walls extending vertically up, forming a sort of water proof tank.

4. TREATMENT OF FLOORS:

For dry locations, generally a filling of 7.5 to 15 cm of dry coarse sand under the floor masonry is specified. A hardcore filling of stones with small stones can be used to fill in voids. The filling should be well rammed but not unduly consolidated. It is observed that a thin layer of cinders and coal tar under a tiled floor acts as a good D.P.C. to prevent the moisture as well as efflorescence. In case, there is possibility of moisture penetrating the floor, it will be necessary to lay a waterproofing membrane of mastic asphalt felt, before a concrete floor is laid. If there is a possibility of the floor is subjected to excessive uplift pressures due to soil and water table characteristics, then concrete floor should be reinforced. 5. TREATMENT OF WALLS:

In case of basements, the external face of the wall is well grouted with a waterproofed cement plaster. This forms the base for the asphalt layer which is continued from the basement floor and extended vertically up covering the whole area of the external wall face. This vertical D.P.C. is further protected by a thin skin wall or protective wall. The horizontal D.P.C. in external walls is generally provided at least 15 cm above the ground level. It is further essential to provide a vertical D.P.C. between the floor level and the D.P.C. level on the inside of external walls. In internal walls, the D.P.C. is provided in level with the upper surface of the concrete floor 6. TREATMENT OF FLAT ROOFS, PARAPETS AND COPINGS: In case of flat roofs, the rain water enters either through the defective parapet wall, or cracked roofing tiles or broken pointing, etc. , The waterproofing treatment given to flat roofs in the various regions of the country is of three types namely, Lime concrete terracing, Lime concrete terracing with flat tiles, and Mud phuska terracing with tiles. To check the penetration through parapets and copings, they should be protected from the weather by providing D.P.C. at various locations such as a D.P.C. covering whole of the roof and then extending up the junction against the parapet wall atleast upto 15 cms height, a D.P.C. for a parapet wall at this height is laid for full thickness of the wall including plaster,etc., a D.P.C. under the coping may be provided where the bricks used are of poor quality. As a general precaution, the tops of the walls should be finished with one course of hard, well burnt bricks set on edge in cement mortar over two courses of slates or dense tiles projecting over the wall.

7. TREATMENT OF PITCHED ROOFS: In case of pitched roofs or sloping roofs, the main causes, of water penetration are: Insufficient lap of tiles or roofing sheets, Insufficient roof slopes or flat pitches and inadequacy of rain water gutters. First two causes are taken care of by proper design and construction as per recommendations. Like flat roofs, the parapet wall should itself be protected by means of a coping of stone or well burnt bricks with a D.P.C. underneath.