Sunny SurlakerIndia is seeing a spurt in urbanization. As we continue to build bigger, faster and taller, reinforced concrete is the choicest of materials to meet the needs of speed and durability. If we understand concrete simplistically, it consists of the aggregate skeleton that is strong, inert and relatively waterproof (except for a small bit of absorption). This aggregate skeleton is suspended in a matrix composed of the cementitious binder and water, what we commonly refer to as the paste. By virtue of the structure of the paste, it is this component of the concrete that is susceptible to porosity, capillarity and cracks. This makes concrete the hydrophilic, absorptive material that it is.
Marketing Manager, Tremco India
Marketing Manager, Tremco India
Therefore the concept of waterproofing too can be simplified as:
- Reducing Permeability / Porosity / Capillarity of the concrete itself with integral waterproofing additives
- Treatment of cracks and joints to prevent entry of water into the structure
- Draining / keeping water away from the porous concrete surface, using surface applied barriers.
Load bearing elements such as walls and columns of superstructure above the podium slab may not align with substructure load bearing elements below. Generally, this type of slab is constructed and placed at ground level parking with multiple levels of conventional residential construction above. The name is derived from the “podium” that separates the two occupancies . Podiums are the areas which are otherwise known as common areas, mostly used for parking and other landscape / garden spaces.
Podiums are structures that may contain a combination of trafficable surfaces (cars, fire tenders, pedestrian / cycling pathways and other similar abrasive loads), garden / plantation areas and other general public use areas.
Waterproofing driven on podiums is the biggest challenge in a successful waterproofing program for a building. Normally the waterproofing systems used are highly elastomeric in nature, which makes them unsuitable in traffic conditions for abrasion resistance. Under traffic loads, the applied membranes often fail, leading to costly repairs.
The inherent problem here, is that the elastomeric waterproofing system is applied to the bare slab and covered with a floating wearable screed that acts both as protection to the waterproofing and a means to providing a slope. Casting this screed layer and the vacuum dewatering process used to enhance the abrasion resistance, causes the screed layer to crack. Further traffic movements cause the cracks to widen and eventually allow water ingress into the system, which further causes waterproofing problems below the podium slab. This damage mechanism is seen in driven-on podiums as well as in car park structures.
Further effects of this damage mechanism are that water along with dripping car fluids / oils, fuel and the abrasive loads, cause damage to the resin-based waterproofing system under the screed, allowing penetration of water through the podium slab and the areas below.
In roof gardens, the damage from the roots of growing plantations, damage the waterproofing system, allowing penetration of water through the podium slab and the areas below.
New generation waterproofing systems for trafficable surfaces are designed to meet the criteria of ASTM C957 / C957M: Standard Specification for High-Solids Content, Cold Liquid-Applied Elastomeric Waterproofing Membrane With Integral Wearing Surface. These systems, based on tough polyurethanes, combine a highly elastomeric waterproof base coat, topped with an elastomeric but very tough wearing coat (with elongation of 120 – 140% and a tensile strength > 27 N/mm2). The interlaminar adhesion between the base coat and the wearing coat forms the basis of success in using these new generation trafficable waterproof coatings. In case of heavy vehicular traffic, the wearing coat can be enhanced using fine silica sand or alumina as a filler in the wearing course. Figures 1 and 2 show the application and finished surfaces for a heavy duty trafficable waterproof coating applied over a car park deck.
Figure 1: Application of a trafficable PU based waterproofing system
These combination trafficable systems are also designed for high UV resistance, resistance to petrol, diesel, lubricants as well as other aggressive salts and chemicals, and are also fire rated. New generation materials are environmentally friendly, low VOC systems, that are very easy to apply. The high crack-bridging ability (>1.5mm) and low abrasion (< 40 mg loss on 1000 cycles, by ASTM D4060) make it a material of choice to provide reliable waterproofing in the toughest conditions. The same systems can be further modified as hybrids of Polyurethane and Methyl Methacrylate (PUMA Systems) to form extreme wearing systems that can provide abrasion resistance and impact resistance, even for traffic by helicopters and airplanes.
Figure 2: Heavy Duty Trafficable Waterproofing System Applied to a Car Park Deck
Expansion and Construction Joints
Expansion Joints and Construction joints are some of the most overlooked components of efficient podium waterproofing. Although the use of construction sealants is seeing some traction, often an incorrect sealant is selected for the application at hand. These joints and transitions account for about 1% of the constructed area, and yet 99% of water ingress into a structure occurs through these interfaces.
These interfaces need to be treated right the first time to ensure a leak-free structure. With this in mind, new generation sealants have been developed. To withstand the rigors of the Indian construction process, these sealants need to perform better in terms of:
- Excellent applicability and adhesion to different substrates
- Applicability to damp substrates
- Over paint-ability
- Very high Movement Accommodation Factors
- Quick curing to service.
Planters and Terrace Gardens
The terrace garden slabs and planter areas also have unique requirements. The planters are often trough shaped, with multiple edges, which makes detailing of Root Resistant Membranes in these areas difficult. Root resistance and durability in submerged conditions is a key requirement.
In case of complicated substrate geometry, it becomes imperative to use a liquid applied membrane. This liquid applied membrane should have the capability to be installed on damp / green concrete, should have good mechanical properties and have resistance to being submerged in salt water. New Generation Moisture Triggered Hybrid PU Coatings provide the optimum combination of elongation, crack bridging, adhesion, chemical resistance and overall toughness. These cold-applied liquid membrane forming coatings can also be modified with a new generation additive to prevent root penetration through the membrane when used in planters or vegetated roofs. The additive functions without damaging the plant roots.
Figure 3: Detailing of Vegetated Planter / Slab using a coating with Anti-Root Additive
However, terrace / podium garden waterproofing needs to be detailed properly to ensure success. One such detailing of a typical product is shown in the figure 3. New generation waterproofing systems for planter / garden areas are designed to meet the criteria of ASTM C836 / C836M: Standard Specifications for High Solids Content, Cold Liquid-Applied Elastomeric Waterproofing Membrane for Use with Separate Wearing Course.
Today’s specifier or constructor has innumerable materials at his disposal, each claiming to be the best. Most of these materials are characterized by generic properties. These properties are suitable for Quality Control to produce batch certificates, but do not address the waterproofing system as a whole. The best waterproofing system is made of Good Base, Good Material and Good Application. Understanding the advantages and limitations of each of the materials used and a keen attention to detailing of the materials is the key to a successful waterproofing system.
That being said, modern materials such as moisture triggered polyurethane coatings, hybrid coatings, and new-age sealants are becoming easier to use, offer better durability, and are very robust for application under the harshest conditions of weather and mechanical resistance. Once the waterproofing job calls for exceptional performance, new generation materials do become imperative to provide a leak-free structure.
- Documentation and drawings from Tremco Inc.