Problem Solving Forum
October 1 - October 5, 2018
Which factors are most important in selecting coatings for new concrete?
Zenith Czora of Durotech Industries, Inc. on
October 4, 2018:
Excerpt from the technical article I published in ...read more Excerpt from the technical article I published in LinkedIn, "When Specifying a Coating System": Before specifying a coating system for a certain project, it is best to do an actual substrate evaluation, whether it is a new or existing substrate, location assessment, environment condition, and function of the substrate or structure. When specifying, a coating specifier should consider the following. 1. Acceptable initial cost – the estimated cost when possible must at least fit within the costumer’s budget. 2. Minimum acceptable anticipated service life of the coating system – depending on the owner’s desire, different choices of coating system with durability comparison should be presented to the owner of the property or his building contractor once assessment has been done. 3. Method of surface preparation – the most appropriate and suitable surface preparation based on the assessment should be included in the specification. 4. Easy Maintenance by touch- up and maintenance topcoat - when it is necessary a coating system should be easy to touch up. 5. Easy application under field condition utilizing equipment that is ready available to the paint contractor. 6. Recoating window that provides flexibility for anticipated delays - In many cases, a project has a very tight installation schedule. This limits many systems in how long it takes to install a given material. Temperature of the surface at the time of installation is critical in selecting a material. Some systems, such as epoxies, are very temperature-sensitive and can vary widely in cure time at lower temperatures. When specifying coating system for concrete floor, polyspartic or novolac epoxy coating is best recommended for concrete floors subject to cold temperature, heavy foot and wheeled traffic, spills and chemicals. Water- based, low-solid acrylic sealerscannot withstand those conditions. Although the durability of concrete stain is dependent on its chemical makeup and polymer type, the stained concrete floor must be regularly treated with waxes or other sealers to maintain the aesthetic appearance. A failure to regularly care for stained concrete can quickly result in a wearing away of the colored surface in high-traffic areas, leaving patches of bare concrete that begin “dusting” as well as absorbing contaminants. Repair of such areas can be difficult. On the other hand, if the floor is light to medium general service and will not be exposed to harsh chemicals, extreme pH substances, wet processing, food production or packaging, toxins or potential environmental contaminants and the like, then polished concrete may be an adequate. However, because polished floors require regular re-polishing or other professional maintenance, they may not be ideal for constant critical traffic operations. Coatings are formulated according to its specific applications and intended use of surface to be coated for a given environment. Coatings that are designed for interior applications cannot be specified for exterior applications. A coating specifier must have a clear understanding between interior and exterior application.Coatings for vertical application on masonry substrates should pass the Wind Driven Rain Resistance Test in accordance with ASTM D6904- 03 (2013). This is an evaluation of the ability of coatings to resist the passage of water through masonry block when exposed to continuous water spray and a dynamic pressure equivalent to a 98 mph wind velocity without exhibiting water leaks or weight gain, or both. Permeability or breathability and elasticity/ crack-bridging properties of exterior coating are most important factors when considering coating systems for concrete walls. For exterior application, specification of color should be done in accordance to the color lightfastness and weather resistance of pigments. The color development is based on desired shade/hue and is achieved by combining at least two pigments, maximum to four pigments either organic or inorganic or combination. Color warranties are based on amount of inorganic pigments versus organic pigments used to create the final color. Not all pigments are suitable for every application. The colous are developed to withstand the weathering and environmental condition preventing from fading and chalking. UV (sun) exposure, moisture, humidity, high temperature and temperature fluctuation lead to color changes and fading. Bright colors such as yellows, oranges and reds fade faster. Heat-reflective pigments give a cool effect and reduce absorption of heat, which helped in extending the life of the binder/resin used in the coating. In summary, thorough assessment and careful consideration on the requirements of area of use, substrate/surface preparation, right application method and conditions are the key factors for successful installation of coating system. Planning, monitoring and review, inspection scheduling, documenting the installation process, maintenance, and repair program should be established for continued performance and satisfaction of the coating system.