Waterproofing: The need and importance:Waterproofing is a very common word used in day to day life. Most of us know and understand the pain of leaking roofs, walls & bathrooms. The damage done by such leakage is not only limited to aesthetics but many times compromises the safety of users & inhabitants. Dampness on interiors may lead to many issues like fungus growth, foul order & spalling of plaster work. Water ingress may result in damage to electrical fittings, potentially exposing people to various hazards such as fire and electrical shock.
Concrete is the main building material used in all civil constructions and as everyone knows concrete always shrinks. Why does concrete require protection? The simple reasons are the porosity, cracks & potential to react with atmospheric gases such as CO2. Apart from that, the structures have various joints & connections which need to be considered & given extra protection.
Some important areas for providing waterproofing are Basements, Exterior Walls and Roofs.
Integral approach:It is very clear that waterproofing is not just about single system or section of construction. Careful analyses needs to be done to understand & design waterproofing system, which will take care of entire building envelope. The integral approach considers all materials, section & factors such as the environment, final use and critical areas. This approach begins at the stage of conceptualization of a project. There are various places and sources from where, water can enter a structure. This could be a ground water (which depends on the water table), rain water & water associated with damp areas & plumbing works. Various products & systems such as sheet membranes, liquid waterproof coating, crystalline systems, water repellants, and integral waterproofing agents are available in the market.
Types of system available:Number of systems are available for waterproofing of the complete building envelope as well as infrastructure. Each system has its own advantages & disadvantages. Table 1, shows some of these systems.
Liquid applied waterproofingThe term means, any system applied in liquid state and then transforms to solid state or integrates itself to effectively waterproof the application area. This mainly includes Flexible cementitious slurries, acrylic, EVA or SBR based elastomeric coatings, Polyurea, PolyAspartic, Polyurethane, Hybrids, thermoplastic acrylates, epoxy based coatings and membranes etc. Crystalline and penetrating treatments are also applied in liquid form but their action is not through sealing but through penetration in to the concrete and reaction with hydration products.
Effectiveness of each system depends on application methods, substrate conditions, exposure/ usage conditions, thickness applied and subsequent maintenance. Differentiation can be made depending on following factors:
- Whether applied Internally or Externally
- Covered or Exposed
- Contact of water is continuous or intermittent
- Trafficked or Non Trafficked
- Exposure to other chemicals except water and CO2
- Access to the area in future, if reapplication or repair is necessary
- Underground (Below Grade) or above ground (Above Grade)
- Expected Movements
- Primary or Secondary system
- Other specific requirements as per user needs or Exposure conditions.
Some standards & specifications:Some of the standards used to test & evaluate performance of waterproofing systems are mentioned in table 2.
There are more standards and a lot of effective test methods to verify and ensure that the waterproofing product being used would serve its purpose and last for the specified life time.
For elastomeric coatings following properties assume utmost importance,
- Tensile Strength, Elongation and recovery after extension. (ASTM D 638)
- Crack Bridging ability (ASTM C 1305)
- Tear Strength (ASTM D 624)
- Adhesion in wet and dry conditions (ASTM D 7234, 719 and 794)
- Water Vapor Permeability (ASTM E 96)
- UV Resistance (ASTM D 4587, 5894, 6695)
Application ProceduresAs for any coating or liquid applied system, surface preparation holds the key. Proper surface preparation will ensure good adhesion, uniformity of coating thickness, proper curing or drying, as well as development of performance properties such as tensile, tear strength and hardness.
Some systems require primer, some are self-priming. Whether to use the primer or not always remains a tricky question. As a general rule, all smooth surfaces such as glass and metal require a primer. Surface with poor strength and high porosity would also need priming / sealing. Various primer systems including epoxy, moisture curing PU, silane / Siloxane based primers and latex based products are widely available in the market. Proper primer shall be decided from manufacturer's literature and project specifications.
Application methods may vary from brush application to multi component spraying. Uniformity and proper thickness will only be achieved, with the use of suitable equipment and method. After application, care has to be taken to protect the application area, until the applied product dries completely. In traffic areas, the traffic shall only be allowed after the applied product cures to attain minimum performance criteria.