DAMP-PROOFING AND WATER-PROOFING COURSE By Fazla Hasan Rabbi (106) Md. Rashedul Islam(108) y

WHAT IS DAMP PROOFING? Dampness a common problem in buildings. It refers to access and penetration of moisture content into buildings through its walls, floors, roof etc. It is important to take measures to prevent dampness. Such measures is called damp proofing. Water proofing is a treatment of the surface or structure in a building to prevent leakage.

Moisture from ground:-The materials used for the foundation and floors absorb moisture from the soil and it rises up the surface of the building, Splashing of rain:-When rain splashes on external walls dampness may enter the interior. Exposed top wall:-dampness enters from the top if the tops of parapet walls are not given sufficient damp proofing course. Condensation: dampness is caused due to condensation of atmospheric moisture, deposited on walls and ceilings. Construction defects:- Improper planning, lack of proper slope in roof, defective pipe fittings, improperly sealed construction joints are constructive defects. CAUSES OF DAMPNESS :-

Effects of dampness:- Ugly patches on walls and ceilings. Plaster softens and crumbles. Materials used for wall decorations are damaged. Stones ,bricks and tiles disintegrate due to efflorescence. Floor finishing may be damaged Woodworks decays due to dry rot. Metal components of building corrodes. Electrical fittings are damaged, Dampness leads to breeding of mosquitoes, growth of termites and germs carrying diseases such as tuberculosis, it also aggravates asthma. Effects of dampness:-

Materials for damp proofing Requirements of ideal materials for damp proofing:- They should be :- Impervious. Durable Capable of bearing the load Dimensionally stable Flexible Free from sulphates, chlorides and nitrates. Inexpensive Materials for damp proofing

Materials used for damping:- Hot bitumen :-hot bitumen,3mm thick may be applied on bedding of mortar or concrete. Mastic asphalt:-semi rigid material obtained by heating asphalt with sand and mineral fillers. It is laid on mortar or concrete bed. Bituminous felt:-flexible material available in rolls. It is laid on flat mortar finished surfaces. Metal sheets:-sheets of lead, copper and aluminum membranes may be used in damp proofing. Lead is the most ideally suited material.

Combination of sheets and felts:-economical and drabble damp proofing sheet is obtained by sandwiching a lead sheet and bituminous felt. plastic sheets:-a relatively cheap method of damp proofing is by laying 0.5-1.0mm thick plastic sheets made of black polythene. This is not a permanent method. Bricks:-quality bricks absorbing water less than 4.5% of their weight may be used for damp proofing. These bricks are laid in 2-4 courses in cement mortar. Mortar:-cement mortar in the ratio 1:3 is used for bedding layers over damp proofing course. It may be mixed with slaked lime to improve its workability. Cement concrete course:-a cement concrete course of proportion 1:2:4 and thickness 75-150mm is laid on masonry at plinth level.

Principles of damp proofing:- General principles to be followed in damp proofing are:- Mortar bed prepared to receive damp-proof course should be leveled. The horizontal damp proofing course should cover the full width of wall excluding rendering. If sheets or mastic asphalt are used, the gap should not be less than 100mm at any point. At joints and corners. Damp proof course should be continuous. Damp proofing course should not be kept exposed on the wall surface. At vertical and horizontal junctions, damp proof courses should be continuous and a cement mortar fillet of about 75mm should cover joints. Principles of damp proofing:-

METHODS OF DAMP PROOFING:- Different types of treatments are used for preventing dampness in different parts of the building:- Foundations:-this is method of protecting foundations of outer walls. An air drain is constructed parallel to the wall. The drain is covered with RCC slab, and gratings are provided at regular intervals, horizontal and vertical damp proof courses are also provided. METHODS OF DAMP PROOFING:-

Treatment for floors:- if there is no damp soil, a layer of coarse sand,75-100mm thick is provided over entire area under the flooring. Then 1:4:8 concrete of 100mm thickness is laid. This layer serves as DPC. the usual flooring is provided over this, If soil is wet, a membrane DPC is provided over the floor area, over which a layer of flat bricks is laid. The usual flooring is then provided.

Treatment for walls: the plinth level should preferably be 450mm above ground level.DPC should be provided over a concrete bed of thickness 100-200mm.the top of the parapet should be provided with capping over the DPC. the wall also needs DPC at the edge of the roof slab.

Methods of waterproofing basement:- Providing foundation drains and DPC:- to release hydrostatic pressure,trenches are made all around the building and filled with gravels etc. such trenches may also be required in buildings if the water table is at a higher level. The trenches lead the water to a catch drain.Horizontal and vertical DPCs are provided in the walls and foundation concrete. Methods of waterproofing basement:-

Providing RCC raft and wall slab:- if the water pressure is high, providing a drainage system will not solve the problem effectively. In such cases the floor slab and wall may be prepared right through the RCC structure and DPC is applied on it.

also known as membrane waterproofing. Asphalt tanking:- also known as membrane waterproofing. Construction of horizontal layers: A leveled course of mass concrete is laid for the flooring area ,over which a 30 mm thick DPC in form of asphaltic layer is provided. A protective layer of cement, concrete or a layer of brick work is laid over the asphaltic layer, after which the flooring is prepared.

construction of vertical face:- A vertical DPC is provided on the external face of the wall. The DPC consist of an asphalt layer of about 20mm built in three coats. This is then protected with a wall of ½ brick thickness.

Using waterproofing compounds:- Water proofing compounds may be grouped to 2:- Waterproofing admixtures:-these admixtures are in powder or liquid form. About 2% of powders are mixed while making cement mortar. when the finishing coat of mortar is provided, these compounds seal the pores in the slab and make them watertight. Using waterproofing compounds:-

Waterproofing membrane system:-these materials are available in the form of paints, they may epoxy or elastomeric and may be applied to roof slabs with rollers ,brush or spray. a minimum of 2 coats are applied to get desired waterproofing.

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