Water is a potent force. Even the tiniest amount can break down the hardest stone when it freezes in a crack. Man-made structures can also be damaged by water penetration. For long-lasting, seamless protection of all types of substrates, many architects and specifiers turn to liquid polyurethane (PU) waterproofing membranes. And with monsoons very strong in many parts of India, it is perhaps the right time to discuss waterproofing materials.
Various waterproofing technologies have been developed to keep water away from penetrating into roofs. One such effective roof coating is fluid-applied coating. The market is abuzz with various types of liquid coating products for roofs in the market. A liquid-applied roofing membrane or coating can itself be the exterior weathering surface, or it may be coated with another UV and weather stable layer.
Benefits galore
When choosing a liquid-applied coating for your project, it is important to consider the existing substrate. Liquid-applied coatings can be installed over virtually any type of surface, from thermoplastic single-ply membranes such as PVC or thermoplastic polyolefin (TPO) to thermoset single-ply membranes such as ethylene propylene diene terpolymer (EPDM), or chloro- sulfonated polyethene (CSPE-Hypalon). They can also be installed over metal, concrete, built-up roof (BUR), modified bitumen (MB), or spray polyurethane foam (SPF).
Fluid-applied roof coatings can be applied as a new roof system on a new roof deck or in a maintenance situation as a re-roofing system over an existing deck. They have many benefits, but they are most commonly used to prolong the life of an existing roofing system whether it is an EPDM or TPO sheet membrane or another fluid-applied roofing system.
These systems contribute to the sustainability of the building structure by extending the life of the existing roof surface and preventing unnecessary roof tear off’s, which contribute a great deal of waste to landfills. If properly maintained, you may never have to tear off the existing roof membrane and a renewable coating can be reapplied every 5 to 15 years.
In addition, reflective coatings are often applied over darker coloured or aged reflective existing roofs to help reduce energy costs. Fluid-applied coatings provide a seamless, monolithic surface that is fully adhered so that water cannot migrate beneath the surface. These coatings are lightweight, often less than 0.5 kg per sq.metre, are self-flashing, and may qualify for immediate tax advantages based on prevailing tax code in your region related to energy saving building upgrades.
Surface Preparation
- While fluid-applied coatings can be applied to almost any substrate, it is important to note that surface preparation is critical for success and longevity.
- Fluid-applied coatings are not to be installed over failed or failing roofs. Deficiencies such as blisters, wrinkles and ponded water conditions must be repaired. A clean, dry, sound, and secure surface is required prior to the installation of a fluid applied coating.
- An infra-red (IR) roof scan or core cuts can help to determine if the roof is a good candidate for a fluid-applied coating.
- Wet and/or damaged areas identified by an IR scan or core cuts must be removed and repaired insulation and coating. Each substrate should be washed with a biodegradable detergent and appropriate power washing or scrubbing equipment.
- Be sure to consult the manufacturer of the sheet goods to determine how long you should wait to install a fluid-applied coating over new sheet goods.
Making the right selection
System selection criteria are probably the most important discussion for a specified, as there are many different types of liquid-applied roof coatings and choosing the right product for a project deserves careful consideration to avoid problems or premature failures. The liquid applied coatings that we will cover here include acrylic, asphalt emulsion, polyurea and Polyurethane.
Acrylic Coatings: Acrylic coating systems are based on acrylic resin and are generally a latex-based system that cures by air drying. Acrylic coatings are amongst the easiest to apply. They are low odour, low cost, and have excellent colour retention, as well as UV and weather resistance with very good initial solar reflectance.
Multiple coats can be applied on hot days, but on the downside, they cannot be applied below 32 degrees Fahrenheit or if rain or dew are imminent. Acrylic coating systems have low tensile strength and are not appropriate for high traffic areas or where ponding water is a problem. They are also not chemical resistant, cannot be applied in heavy mils, and have extended cross-linking time. However, when used appropriately, acrylics can greatly enhance the appearance of a roof.
Asphalt Emulsion: Asphalt emulsion is a mixture of asphalt particles and an emulsifying agent such as bentonite clay and water. These components are combined by using a chemical or clay emulsifying agent and mixing or blending machinery.
Emulsions are user-friendly and provide good water resistance. However, they are also temperature dependent, cannot resist the high movement of modern buildings, have somewhat of an odour and require protection and reinforcement for superior longevity. They are also dark in colour so they will cause the roof to heat up when exposed to the sunshine.
Polyurea Snap Cure Systems: Polyurea coatings are either solvent based or 100 percent solids. Depending on the formulation, they are typically two-component and cure to form films with limited elongation and high tensile strength.
Polyurea coatings can be applied in heavier single passes up to 40 mils thick and can be applied to vertical surfaces with significant film build. Spray-applied base and top coats can be applied the same day, providing a quick return to service with very durable physical properties and low VOCs. These coatings can be rained on or walked on often within minutes of application.
However, polyureas can have adhesion issues and suffer significant loss of physical properties over time due to UV degradation. Plural component equipment is very expensive and a good application is heavily dependent on the applicator, more than with other fluid-applied coatings. There is potential for an off-ratio mix if the equipment experiences issues, and there is significant overspray risk.
Polyurethane Coatings: Polyurethanes are one of the most durable coatings on the market today and have found application in the corrosion and construction protection markets because they provide a unique combination of flexibility, weather resistance, as well as chemical, abrasion, and corrosion resistance.
These coatings also provide reduced VOC emissions, superior coating thickness, and edge retention. A well-formulated coating provides the advantage of fewer required coats, reducing cost per application by reducing labour, and the higher level of performance requires less surface preparation and the ability to self-prime. Furthermore, polyurethanes have faster curing times, allowing for increased productivity and driving their widespread acceptance across the protective markets.
Polyurethane coatings come in both single component (moisture cure) and plural component (chemical cure) systems with different speeds of reactivity. Single component polyurethanes are moisture cured and offer longer working life, while plural component products have a standard-to-fast cure time, limiting the window of opportunity when installing. However, the faster cure time provides a faster finish, which limits defects due to rain or environmental contaminants such as leaves or insects.
Factors affecting proper selection
There are several factors to consider in selecting the proper liquid-applied coating including the time of year of application, which will determine the weather, temperature and humidity. Geography, expected longevity, and use of the roof including mechanical equipment and foot traffic are also important, as are aesthetic considerations.
Some may think of roof aesthetics as secondary but consider that higher buildings surrounding the project will have a clear view of the roof. Flammability and code requirements, cost (life cycle), the mil thickness and slope are also important considerations.
Summary
India in recent years has witnessed traction in new constructions and renovation works. Protecting industrial, commercial or residential buildings, sports facilities, bridges, stadiums, museums and storage tanks is critical to reducing repair and replacement costs. Polyurethane coatings are capable of satisfying even the toughest of demands and thus make a substantial contribution to the long-lasting functionality of roofs.
Source: Covestro India Pvt Ltd
© Coatings Special by Chemical Today Magazine
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