CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.
Issue link: http://coatingspromag.epubxp.com/i/796818
44 MARCH 2017 COATINGSPROMAG.COM Science Behind It Elastomeric Envelope By Jamie Barnett, Technical Specialist for SureCoat Systems M oisture is one of the most destructive elements for wall assemblies. On the Hilton Houston NASA Clear Lake Hotel project, Surmac's solution to water intrusion was to apply two layers of StrucSureCoat at an average of 10 mils (254.0 microns) wet film thickness (W FT) each. T he StrucSureCoat system, which uses chemistr y originally developed to protect roofs, helped to water proof the hotel 's exterior. What's In the Bucket StrucSureCoat is a single-component, epoxy-enhanced, hybrid elastomeric coating. It was developed using polymers specific to the marine industry. ese resins and polymers combine to create properties that enable coated surfaces to withstand constant moisture and extreme thermal cycle movement without drying out or sagging during their life cycle. ese qualities make sense for marine applications, but with the sun's rays and fluctuation of outdoor temperatures, they also fit well with the needs of the building envelope. Waterproofing Properties Most exterior coatings are only water resistant for a short time; once they dry out, they lose the ability to repel moisture; they're no longer resistant. e typical perm rating of paints and coatings — the rate at which moisture travels through — is often between 5.0 and greater than 15.0. e perm rating of StrucSureCoat is 0.0025, which makes it waterproof, not just water resistant. e waterproofing and protective thermal properties include protection against wind-driven rain. Moisture penetrates through a StrucSureCoat membrane as fast as water goes through a sheet of aluminum. Part of being waterproof is the ability to stay flexible and monolithic. It's important that the coatings don't lose their permeability, or waterproofing abilities, and become brittle over time due to the effects of heat and ultraviolet (UV) rays. Because StrucSureCoat has a highly thermal emitting property, it releases approximately 88 percent of the heat that hits the surface back into the atmosphere, reducing heat transfer and radiant heat effect. is is what reduces interior temperatures and offers heat gain savings on cooling cost. It also reduces thermal cycle movement of the walls themselves that can cause gaps and cracking at doors and windows. If a coating tears or cracks, then moisture can be trapped between the wall and coating, causing significant but hidden damage to walls. Moisture intrusion will activate salts in concrete and masonry materials, including stucco, plaster, and shotcrete causing the pH to drop and activate conditions for deterioration, which can reduce structural integrity. In concrete tilt-up buildings, the rebar can become wet, then can rust, swell, and cause spall damage to the exterior walls. Loss of structural integrity of the building components becomes a real risk. Mold and mildew growth can occur, causing further issues. at's why cracks are important to control. e word "elastomeric" indicates that the coating has qualities of an elastomer. ese coatings are made with synthetic rubber materials to give them the ability to stretch, much like a rubber band. However, as with a rubber band, there is a breaking point, and elements such as UV rays can degrade the elasticity of the material. StrucSureCoat remains monolithic by bridging the surface of the building without becoming too brittle during temperature changes. Too much elongation will cause a coating to lose memory and become brittle and crack like an old rubber band. If there isn't enough elongation in a coating, again it will become brittle at cold temperatures. Rapid thermal cycles and freeze-thaw conditions can cause these materials to crack. With 400 percent elongation at 72° F (22.2° C), StrucSureCoat stays flexible by using microscopic hook-like chains of molecules that are intended to open and close repeatedly. W hen heated, they open, release, and expand in a 360-degree pattern. As the membrane cools, the chains contract while closing and reattaching to the substrate. At 32° F (0° C), StrucSureCoat has 160 percent elongation. With these elastomeric and monolithic qualities, a coating that has been used in marine applications can there- fore be applied to wall assemblies. CP