Waterproofing of Below Grade Structure

For homeowners and builders, preventing water out from a below-grade structure, commonly known as a basements, can be a significant challenge. Whether building a basement, foundation, or underground parking garage, effective waterproofing is crucial to avoid costly damage and maintain a safe environment. The selection of the right waterproofing system depends on various factors, including the basement's depth, groundwater level, foundation type, and the feasibility of waterproofing from positive or negative sides.

Case Study – Basement Bliss Turned Bust

A few years ago, Mr. Gupta, the owner of a beautiful bungalow in DLF Phase 1, Gurgaon, reached out to us. His house, constructed just a year before, featured a 3500 sq. feet basement designed for a home theatre, bar & lounge, entertainment area, and a well-appointed home office. Our waterproofing company, Dry Shield, was called in to inspect the basement, which experienced major seepages during rains, significantly damaging the entire interior. Expensive equipment, furniture, wall paneling, and flooring were all rendered unusable.

During the initial construction phase, I had met Mr. Gupta and recommended waterproofing from the positive (outside) side, providing a quote from Positive. However, the civil contractor advised against it, believing it unnecessary because the water table was 300 ft, and both the contractor and Mr. Gupta assumed that Gurgaon experienced little rainfall. Now, faced with substantial damage, Mr. Gupta wanted DryShield to undertake the waterproofing. We successfully waterproofed the basement at a cost of almost INR 76 Lakhs. However, the total expense, including rework and damages, amounted to nearly 1.80 crores. Compare it to our original estimate of INR 4.80 lakhs before construction had begun a few years back.

This case study emphasizes that the actual cost of waterproofing is not exorbitant. Instead, the cost of not doing waterproofing becomes significantly expensive. Selecting the right product, application, and timing for waterproofing is crucial. Conducting below-grade or basement waterproofing from the positive side (outside) is advisable, as it is cost-effective and more efficient. When it's not feasible from the positive side, negative side waterproofing should be employed, using suitable products.

This case study vividly illustrates the importance of choosing the right waterproofing solution during construction, tailored to the structure's specific needs.

Now, let's explore some popular waterproofing options for below-grade structures. Though consulting with a professional waterproofing expert is essential to determine the best system based on site conditions:

?1. Elastomeric Modified Bitumen: These cold-applied modified bituminous coatings made from a blend of special resins, rubber, and mineral stabilizers, reinforced with special water-repelling agents and sometimes with fibre also. This modified bitumen is highly resistant to water and chemicals. Applied in a thick layer over the concrete foundation or basement walls, they create a waterproof barrier with a very high elongation of 600% and above. Proper application and curing are crucial before backfilling or finishing the walls. It is advisable to protect them with either plaster or a protection board. Elastomeric Modified Bitumen is suitable for situations where the water table is low, and waterproofing is done from the positive side of the structure.

?2. Pre-formed Waterproofing Membranes: Made from synthetic materials like HDPE, APP, PVC, EPDM, or TPO, these sheet membranes are applied in single or multiple layers to form a continuous moisture barrier. Highly flexible, they can accommodate the natural expansion and contraction of the foundation. Pre-formed Waterproofing Membranes are appropriate for high water table conditions, and waterproofing is done from the positive side of the structure.

?3. Cementous Coatings: Various cementitious coatings are very popular for waterproofing basements, especially retaining walls. Options include Cement slurry modified with an over-the-counter Polymer, a two-component cementitious coating with a premix Powder and Polymer (ratio 1:0.25, 1:0.5, or 1:1 by weight), or a crystalline cementitious coating. These are used when the water table is very high, and waterproofing is done from the positive side of the structure. It's advisable to protect them with plaster or a protection board.

?4. Bentonite: Bentonite is a natural clay that swells when wet, and is commonly used in below-grade waterproofing systems as a self-sealing barrier. It can be mixed with water to create a slurry, which is applied to the foundation walls or poured as a solid sheet. When wet, the clay expands to create a watertight seal.? Though not very popular in India, Bentonite is used in high-water table areas.

?5. Drainage Systems: While not widely adopted in India, installing a drainage system is another method to waterproof below-grade structures. This includes interior or exterior drainage, such as French drains and sump pumps, redirecting water away from the foundation to prevent seepage.

?It's important to note that proper installation is crucial to achieve the effectiveness of any of these waterproofing options. Consulting with a professional waterproofing contractor is recommended to determine the best choice for your specific below-grade structure and ensure proper installation.

?