By: Mr. Tan Ju Kuang
Constructing a roof, be it a concrete or metal roof can be an easy task for a typical roofing contractor. Concrete roof slabs are usually built with a waterproofing system that is designed with conventional system such as crystallization admixture, exposed EPDM membrane, liquid applied membrane such as acrylics and polyurethane coatings. Other than concrete roof, metal decking roof is also popular in factory construction where the metal sheet naturally provides the waterproofing properties it needed for a factory set up. Metal sheets overlap each other and fasteners provided the anchoring requirement to hold the metal deck in place.
Concrete are prone to cracks due to shrinkage and cracks could compromise the waterproofing membrane at the flat roof. Similarly, metal deck and metal screws corrode over time and this could lead to issue relating to water seepage. This can be a pressing issue when the roof starts to leak and a solution is required.
Started in the early 80’s, standard roof coating systems use to treat concrete roofs from further leaks include cementitious coating, torched on Bituminous Membrane, rolled on acrylics coatings and polyurethane coatings. Conventional coatings like these while they offer certain benefits, would not be considered a long-term solution today. Most of them could not be exposed to UV directly as UV’s will degrade the system causing premature failure of the coating or membrane. Epoxies and cementitious coatings are very rigid and are not designed to handle cracks due to poor elongation properties. Epoxies are likely to chalk and polyurethanes will degrade when exposed to the tropical climate with high UV and thermal expansion. In addition, the majority of the waterproofing membranes require a layer of protection screed to be laid over it. When this conventional system fails and the roof starts to leak, an exposed waterproofing with high abrasion resistance and stable under the UV is ideal for a re-waterproofing purpose as you do not have to remove the existing screed and waterproofed membrane and just lay the new membrane over it.
Introducing Polyurea. Polyurea is a spray on elastomeric system which can be applied on both concrete and metal roof to resolve problem associated with water seepage. Polyurea can be applied to a thickness of 2-3mm, which will then give you an elongation property above 300% and a tensile strength of >15Mpa. Sprayed as a single coat system, it eliminates joints and overlapping within the coating itself and hence reducing the chances of leak from happening. As a roof coating repair system, it can be sprayed directly on existing surface after sufficient surface preparation is done, thus reducing the need to hack and remove existing screed which could be costly and time consuming. Furthermore, the shut down time of the affected areas can be reduced to a minimal due to the quick set nature of the polyurea resin, typically in less than 2 minutes after sprayed.
Nevertheless, polyurea does have its limitations. The application of polyurea requires the operator to be skilled and well trained as the operation requires multiple set up of spray machine, air dryer and air compressor. The cost of maintenance of the spray machine and accessories can be high as the machine are supplied by niche vendors in the market. Depsite all the advantages it brings, the polyurea system also comes at a higher cost compared to conventional waterproofing system. The cost factor of this system often discourages wide spread use of polyurea for customer who understand its cost benefit analysis.
The growing trend of green roofs being designed and built in the country also mean that conventional waterproofing with joints/seams will not work as root penetration attack on the coating itself can be an issue. In this case, polyurea are ideal as many product manufacturers have test their polyurea for anti-root penetration.
Among other typical uses of polyurea coating includes portable drinking water tank lining systems which required local authority drinking water certificates, theme park coating where coatings are subject to constant immersion of chlorine and UV exposure as well as foot traffic.