There is a subtle difference between damp proofing and waterproofing. The general objective of both is to minimize the travel or passage of water through a material.
People face a lot of problems due to leakage of water/seepage/dampness in buildings soon after construction and during life of buildings. Problem is faced by the occupants for repairing the same on permanent basis. This is a source of unhygienic condition, health hazard, etc., besides life of the building is shortened considerably.
Following are three types of problems:-
This is mainly on the floor, walls of ground floor or even walls of upper floor. The main source of dampness is due to low lying area and moisture rising from ground / foundation / earth filling below floor. It is also due to not providing proper Damp Proof Course at plinth level and due to defects in construction of DPC and foundation.
Leakages are found from various sources viz. wet areas in buildings (toilets, bathrooms, kitchen, roof, terrace, water supply & sanitary service installations, drainage & sewerage installations, overhead water tanks etc
One main source of seepage is leakages as stated above. Besides dampness is formed due to defective constructions / materials of external walls of building.
CAUSES FOR DAMPNESS IN DIFFERENT ELEMENTS OF STRUCTURE
The main causes which create dampness/leakage come under three heads:
(a) Inadequate investigation, defective planning/ design.
(b) Inferior quality of materials used in construction and
(c) Poor quality of workmanship
Though the literary meaning of both sounds same however almost all codes have defined these two separately in terms of form of moisture, based on methods to treat it which differs in terms materials used, thickness of preventive layer applied and of course methods of applying it. CPWD ( Indian government building department, American Concrete Institute as well as International Residential codes have defined both.
The American Concrete Institute (ACI 515.1) defines waterproofing as a treatment of a surface or structure to resist the passage of water under hydrostatic pressure, whereas damp proofing is defined as a treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.
Damp proofing is intended to keep out soil moisture, while waterproofing keeps out both moisture (and water vapor) and liquid water. The International Residential Code (IRC) specifies that “any concrete or masonry foundation walls that retain earth and enclosed interior spaces and floors below grade shall be damp proofed from the top of the footing to the finished grade.” Waterproofing is required only “in areas where a high water table or other severe soil-water conditions are known to exist.”
The purpose of the damp course treatment is to prevent rising of dampness from the sub-soil or foundation reaching the brick masonry at the plinth level. Damp proof treatments are generally flexible i.e. bituminous-based or bituminous-based membranes. Polymer membranes made out of butyl rubber based formulations can be used for achieving damp proofing of basement RCC/CC floor surfaces, provided the membranes are applied with appropriate latex type adhesive to develop proper bondage to the concrete and remain undamaged in the process of receiving a layer of concrete over them and are sandwiched between two concrete layers. It has one main purpose: stopping the transference of ground moisture through masonry or concrete. Typically the damp proofing coating cured thickness is less than 10 mm thick. Damp proofing is not intended to keep all water and moisture out, but rather its goal is to retard moisture infiltration by blocking the capillaries of concrete or masonry, which slows water penetration.
The damp proof treatments must be preceded by collateral measures of sub-soil water collecting systems, proper construction of rainwater collection and disposal systems and impervious plinth protection all around the structure.
Similarly in the CPWD Schedule of Rates, 2002 under the Sub-head 4.0—Concrete Work, the items of providing 40mm thick cement concrete 1:2:4 and applying a coat of residual bitumen of penetration 80/100 @ 1.70 kg per square meter come under damp proof. The treatment carried out to the basement also comes under the classification of damp proof course. In the same schedule of rates, there is a special Chapter on waterproofing (Chapter: 25).
The goal of building waterproofing is to prevent as much water as possible from entering the building, and to provide outlets and drainage so that if water does get inside, it is not allowed to remain. Many designers while designing simply forgets that there is going to be water.
Waterproofing materials have the ability to seal cracks that develop over time due to their elastic, flexible nature and the thickness of the applied coating. Waterproofing materials also are designed to withstand hydrostatic pressure and are often in excess of 40 mm.
Treatment to the roof and other parts of the structure comes under the nomenclature of waterproofing and not damp proofing. Waterproofing treatment ensures or expected to ensure foolproof mechanisam against ingress of water. The problem with the penetration of water into the RCC is that it initiates the damage and the damage in course of time gets propagated to the other areas of the structure causing more and more damage.
Waterproofing is essential in areas where there are significant rain and high water tables or building is near to water bodies like lake, river etc. As water enters the ground, it collects around the foundation. The higher the water rises up the foundation, the greater the hydrostatic pressure exerted against the concrete or masonry surface. This is especially true in areas with clay soils, as clay will absorb and hold more water than granular soil. This hydrostatic pressure forces water through porous concrete/ masonry. So the sub-grade depth of the concrete structure, the degree of inherent hydrostatic pressure in the area and the use of the interior space are important criteria to consider when determining whether damp proofing or waterproofing is appropriate.
Of course damp proofing will not seal large pores or cracks. It also cannot take care of poor workmanship resulting from coarse or careless back filling, limited thickness of DPC, brittle material used etc. It will succeed if there is adequate foundation drainage leading to absence of hydro static pressure.
Hence whether to adopt damp proofing or water proofing will depend on many factors like soil type and soil conditions, water table, drainage in the surrounding area, amount of damp or moisture that one may allow within the structure. It is natural that waterproofing will definitely cost more than damp proofing. One has to make a right choice based on discussions above.