Making Sense of Masonry Coatings
‘Prior Planning, Preparation and Practice Prevent Poor Performance,’ is a military motto. It should also be the inspiration for every painting contractor, especially when it comes to applying effective and lasting masonry waterproof coatings, according to our expert.
Properly treating masonry substrate, whether it’s the exterior of a commercial building or a residence, minimizes or eliminates the problem of moisture intrusion into the substrate, said Jeff Spillane, senior manager of training implementation for Benjamin Moore. “Concrete block is like a rigid sponge that allows any excessive moisture to easily penetrate the substrate if it’s not well-coated,” he said. “But it’s also important to keep in mind that most liquid coatings won’t hold back water, only moisture vapor.”
When a painting contractor has to decide how to most appropriately treat a block-constructed commercial building, residential unit, or a cinder block retaining wall in the backyard of a home, what considerations should be part of the decision-making process?
One of the most important factors with new construction, Spillane said, is whether the masonry has had enough time to cure before any primer, filler, or other coating is applied. Ideally, conventional block construction should have cured for at least 60 to 90 days, he said, while tilt-up construction requires at least 30 days to cure. Although products are available that can be applied after less cure time, the majority of products used as masonry coatings require this relatively lengthy cure time to ensure that coatings will last, Spillane said.
CONDITIONS AND STEPS NEEDED FOR SUCCESSFUL PREPARATION AND APPLICATION
Once the appropriate cure time has been established, it’s time to evaluate the pH level of the concrete, Spillane said. A pH of 8 or 10 is optimal for good results, he said. If the pH is as high as 13 or 14, “you may have to acid-treat the substrate to balance the pH.”
Next, make sure weather and environmental conditions are conducive to successful application of a water-resistant or waterproof coating. Ideal conditions are 70˚ with 50% relative humidity, Spillane said, acknowledging that expecting these conditions isn’t realistic. “As you move away from those numbers, though, you may sacrifice overall performance of the system,” he said.
Rick Watson, director of product information and technical services for Sherwin-Williams, pointed out that some coatings can tolerate an outside temperature of between 35˚ and 110˚ F. “It is important, however, not to apply the coating in direct sunlight because the surface could dry too quickly, potentially trapping moisture within the coating,” Watson said. And, he said, the coating can ‘bubble’ if the surface is too warm when the coating is applied.
If the weather and position of the sun are cooperating, inspect the substrate and make sure it’s clean, sound and dry, Spillane advised. Any contaminants, such as mildew or efflorescence (the white residue created when water penetrates the substrate), should be cleaned off and neutralized with a cleaning product that can remove etching in the block before any coating is applied. Efflorescence that’s left behind, he explained, can cause premature failure.
“All concrete contains impurities,” Spillane said, “and if moisture passes through the substrate, all those impurities are brought to the surface.”
Before applying a coating, patch any cracks or holes, Watson recommends. Walls should be dry, he added, meaning that the surface should not contain more than 15% moisture as measured by a moisture meter.
A concrete and masonry waterproofer can fill any remaining pinholes, said Stephen Munshi, product manager for Behr Process Corporation.
“You want to be sure every pore gets filled by spraying and back-rolling carefully with the appropriate millimeters, per manufacturer specifications,” Watson said.
A masonry sealer is another option, Spillane said. The Paint Quality Institute (PQI) points out that a masonry sealer has very little or no pigmentation, whereas a primer is pigmented. The PQI advises painting contractors to choose a sealer that is indicated specifically for new masonry. “If the surface is currently painted, a sealer may not be required,” Spillane said. “This will be determined by the current condition of the existing paint film.”
The finish coat should dry as a solid film, as if you’re, “putting a piece of plastic over the entire building,” Watson said. By applying the finish coat as a continuous film, you’re helping to prevent several problems, including water damage, mold and mildew growth, and possible spalling and peeling of the paint on the substrate, he said.
If you’re in a hurry, Sherwin-Williams’ Loxon XP Masonry Coating is formulated to be applied as early as seven days after masonry has been constructed, Watson said. Formulated to counteract the effects of high-alkaline content and efflorescence, it has flexibility and tensile strength like that of an elastomeric coating. “But waiting 30 days at minimum for curing is still the ideal standard,” Watson said.
ELASTOMERIC COATING CONSIDERATIONS
PQI says elastomeric wall coatings—exterior acrylic latex masonry paints designed to be applied in thick films (about 10 times as thick as regular paints)—are tough and flexible, and stretch as cracks underneath the surface open and close. These coatings can be tinted to a light color.
A major consideration for deciding to go to the next level and use an elastomeric product on masonry instead of a standard latex paint, the experts say, is geography. “If the client is located in a dry climate like Arizona, for example, you probably don’t need an elastomeric coating on most masonry,” Watson said. “But if the client is located in the Midwest, Northeast or Florida, then an elastomeric product may be appropriate.” He said an elastomeric coating is often applied up to 40 millimeters in thickness. “Without the proper coating on masonry in humid areas, water—taking the path of least resistance—can penetrate the surface. And when the water freezes, it contracts and expands in a cycle that can lead to spalling, where the concrete and coating just pop off.” Elastomeric coatings are especially needed, Spillane said, where there are noticeable cracks or some shifting of the concrete.
But even if the climate calls for the product, an elastomeric coating is only appropriate for walls where water comes in contact with the front of the masonry, explained Eric Serrano, the channel manager, floor & specialty products for Behr Process Corporation. A retaining wall in a backyard, for example, isn’t an appropriate surface for an elastomeric coating because pressure from water coming from behind the wall, “can push the elastomeric coating out,” Serrano said.
NEWER PRODUCTS MAY ACCOMPLISH MORE
Clear siloxane waterproof coatings may be appropriate for unpainted masonry surfaces, Spillane said. “They may penetrate more deeply into the substrate,” he said. He also noted that more masonry coatings on the market have lower volatile organic compounds (VOCs), too.
In addition to Loxon XP Masonry Coating, for higher-alkaline surfaces with signs of efflorescence, Watson said, painting contractors can choose the reflective pigment version of that product, which reflects solar rays back into the atmosphere and helps reduce the surface temperature.