Various permutations and combinations in specifications can avoid such problems, for example, the following options for waterproofing can be considered:
- Give a water impermeable coating on the finished surface of IPS – Though this method can prove effective on a short-term basis, may create problems subsequently. It is observed that the coatings based on pure solvent-based polymers, though effective do not function for a larger duration due to their requirement for a thoroughly clean and dry surface.
From an economic point of view also these coatings turn to be fairly expensive and basically being a costly commodity, cannot be given in a bigger thickness. These coatings also need to be taken care of for the abuse of UV rays, which involves improvising the formulations knowledgeably with proper UV-absorbent chemical inputs.
2. In order to take care of the above shortcomings, these days, polymeric cementitious coatings are more preferred the world over. These systems have better adhesion to the surfaces and can tolerate to an extent deficiency of the surface like slight wetness and micro dusting etc.
The thickness of these coatings also is 8 to 10 times more than pure polymer coatings. However, in this type also, one needs to select the polymer judiciously so that the UV interaction and disintegration due to the same can be avoided.
Though the systems based on the comatrix of polymer and cement are more preferred due to their composite properties like adhesion, waterproofing, flexibility, resistance to UV rays, and improved resistance to wear and tear, a discerning specifier has to bear in mind that after all this system is a film and it is quite possible that due to any physical damage to the concrete surface underneath the coating, the coating itself can get damaged.
However, by and large for inaccessible RCC slabs or terraces above, treatment is proved to be very useful and effective even in high rainfall areas like coastal regions or mountain ranges.
3. Another practical approach adopted is to incorporate these water-based polymers in the IPS itself. This increases the water impermeability of the IPS and at the same time decreases the extent of shrinkage cracks due to an increase in the flexural strength of the matrix.
Additionally, the use of polymers in cement concrete/ mortar is found to increase the adhesion of the concrete mortar to the surface. This integral addition of polymer in mortar is very useful and beneficial for any high-rise structure if applied in the form of plaster, particularly for the fact that it becomes difficult for any engineer, either from the client’s side or from the contractor’s side to supervise the work effectively on the floors beyond 3rd or 4th floor.
The permeability of polymer-modified mortars has been experimentally checked by various researchers including the authors. The studies have revealed that at approximately 4 percent dosage of polymer to cement, a substantial reduction in permeability is observed.
Though on a long-term basis, incorporation of polymer in concrete/mortar is very useful to the structures from a waterproofing point of view or even otherwise, there is also an important role of economics, which comes into play.
Since the consumption of polymer in the earlier case of waterproofing, the film is to be considered only on the surface spread basis, and comparatively, in a small thickness, the cost per unit will be substantially less. However, when the polymer is to be dispersed throughout the mass of concrete/mortar then depending on thickness the consumption of polymer substantially increases, adding to the cost.
But the fact should not be overlooked that the addition of polymer throughout the mass of concrete/mortar adds to the durability of the structure due to a substantial increase in impermeability, adhesion, flexural strength (i.e. decrease in shrinkage cracks), and added resistance to in-service aggressive attacks by environmental pollutants or even carbonation. Once again the prevailing wisdom will decide the course of selection of the option.
4. Looking at the cost and benefit ratio, another method is gaining ground and acceptance with the consultants and clients. In this method, the polymer cementitious comatrix film is applied to the existing RCC slab or the mother surface.
Obviously, this application is done in a way that no pinholes or holidays are left on the surface. This layer is tested for impermeability by ponding test and then is sandwiched by completing subsequent brickbat Coba or the IPS as the case may be.
In this option, even if the IPS develops cracks due to shrinkage etc. (which can be minimized by adding anti-shrinkage compounds and good curing) and the water percolates through the section, it will be totally stopped at the polymeric cementitious film which is applied on the bare slab. In this case, though the water is effectively stopped, the cost would not unduly increase, as the polymer demand involved will be only for the film formation.
Moreover, the film is not likely to get damaged due to wear and tear as the same is sandwiched between two strong phases viz. RCC slab and subsequent BB Coba and /or IPS. In our opinion and experience, this method is more acceptable due to its cost and effectiveness to fulfill the requirement of healthy and durable structures.
All the four options illustrated above can be applied for the waterproofing of toilets, baths, swimming pools, flowerbeds, overhead and under-ground tanks, etc.