Dampness | Damp Proofing Construction

Dampness
Damp Proofing Construction

• Dampness indicates the entry of presence of moisture in building due to several causes such as rainwater penetration, a rise of groundwater, condensation in building, improper drainage & orientation, use of defective materials or bad workmanship. 

• The treatment given to prevent leakage of water from the roof is called water-proofing.
• The treatment given to keep the walls, floors, and basement dry is called damp-proofing.

Causes of Dampness

• Dampness rising through the foundation walls. Moisture from the wet ground may rise well above ground level on account of capillary action.
• Splashing rainwater which rebounds after hitting the wall surface.
• Penetration of rain-water within unprotected tops from walls,  parapets, compound walls, etc.
• In the case of sloped roofs, rain-water may percolate through a defective roof covering.
• On condensation, this moisture present in the atmosphere becomes deposited on the components of each building.
• In the case of flat roofs, inadequate roof slopes, improper rain-water pipe connections and a defective junction between roof slab and parapet. 
• Due to leakages in wet regions of a building which combine kitchen, bathroom, water closet, etc.
• The leakages could be on account of the use of sub-standard plumbing fittings and fixtures as well as faulty execution of work and bad work­manship.

Effect of Dampness

• This causes efflorescence which may presently result in that disintegration about bricks, stones, tiles, etc.
• It may result in softening and crumbling of plaster.
• That may cause bleaching also flaking of paint include the formation of coloured patches.
• It may lead to the corrosion of metals.
• It may damage electrical fittings.
• It promotes the growth of termites.
• It breeds mosquitoes and creates unhealthy living conditions for the occupants.

Methods of  Damp-Proofing

1. Membrane damp-proofing
2. Integral damp-proofing
3. Surface treatment
4. Guniting
5. Cavity wall construction

Membrane Damp-proofing

• This consists of providing layer or membrane of water repellent material between the source of dampness and the part of the structure adjacent to it.
• This type of layer is commonly known as a damp proof course (D.P.C.)
• It consists of materials like bituminous felts, mastic asphalt, silicon, polymers, plastic or polythene sheets, cement concrete, etc. 
• Depending upon the source of dampness, D.P.C. may be provided horizontally or vertically in floors, walls, etc.
• The provision of D.P.C in a basement is normally termed as 'tanking.’

Integral damp-proofing

• A dividend of certain water-proofing compounds by the concrete mix to improve its impermeability.
• Such compounds are available in the market in powdered as well as liquid form.
• The compounds made from clay, sand or lime (chalk, fuller’s earth, etc.) help to fill the voids in concrete and make it waterproof.

Surface treatment

• Surface treatment consists of filling up the pores of the surfaces subjected to dampness.
• The value of water repellent, metallic soaps so as calcium also aluminium oleates including stearates is much effective in protecting the building upon the heavy rain.
• The bituminous solution, cement coating, transparent coatings, paints and varnishes fall are also used.
• Other surface treatments given to walls are lime cement plaster.
• The walls plastered with cement, lime, and sand mixed in proportions of 1:1:6 are found to serve the purpose of preventing dampness in the wall due to rain effectively.

Guniting

• This consists of depositing an impervious layer of rich cement mortar over the surface to be water-proofed.
• The operation is carried out by the use of a machine known as a cement gun.
• Each assembly broadly consists from a machine having arrangements for mixing materials including a compressor as forcing the mixture below pressure within a 50 mm dia flexible tube pipe.
• The hose a pipe has a nozzle at its free end to which water is supplied under pressure through a separate connection

Cavity wall Construction

• This consists of shielding the main wall of the building by an outer skin wall leaving a cavity in between the two.
• Each cavity prevents the moisture of travelling from the external to the inner wall.
• That consists of two walls with a 5 cm to 8 cm cavity within them
• The outer wall is also known as outer leaf and  thickness to 10 cm (half brick)
• Some inner wall is sufficiently thick also strong to carry  those imposed load safely
• The minimum thickness of the inner wall is 10 cm (half brick)
• The provision of a continuous cavity in such wall efficiently prevents this transmission of dampness above head the inner wall.

Purposes or advantages

• There is no contact between every two leaves except at the wall ties impervious material, there not a possibility of moisture moving from the outer leaf before the inner
• Then a layer of air in the cavity being non-conductor of heat from external face to the internal one
• This wall has a 25% greater insulating value than solid walls
• They have good sound insulation property
• They are economical.

Materials used for Damp Proofing

• Flexible material:- bitumen felts, plastic sheeting (Polythene sheet), etc.
• Semi-rigid materials:- Materials like mastic asphalt or a combination of materials or layers.
• Rigid materials: A materials same first-class bricks, stones, slates, cement concrete, etc.
• Grout consist like cement slurry also acrylic-based ingredients polymers

A requirement of the ideal material for Damp proofing

• It should be impervious.
• It should be strong and durable.
• It Should be capable of withstanding both dead as well as live loads without damage.
• It should be dimensionally stable.