Stampable overlays provide people an option to spruce up a plain concrete slab when reinventing a backyard space or a room in a home. This type of overlay is used to create designs resembling stone, granite, tile or slate for both outdoor and indoor floors. With a variety of colors available, a stamped overlay can be acid stained or dyed. Another color option for overlays is using liquid or integral colorants in the mix.
There are a variety of mixes available for stamped overlays including cementitious acrylic compounds and polymer modified mixes. Along with completing the proper steps for the surface prep, it is also essential to determine the application thickness based on the condition of the slab and the desired end product.
Achieving proper surface prep
If contractors fail to follow basic steps and cut corners, they will find unsatisfactory end results, says McKinnon Material’s Products Specialist and Training Instructor Buster Osteen. “If you start out with a bad prep then you are going to end up with a bad job,” Osteen says.
A successful surface prep begins with a visual inspection of the concrete, says Concrete Coatings Director of Operations Brian Anderson. “You are going to make a determination visually whether or not it is a good candidate for a coating,” he adds.
Contractors should start by evaluating cracks. “Overlays work better if you have a sound piece of concrete that doesn’t have a lot of structural cracking,” Osteen says. Application of overlays works best with a piece of concrete that was put down properly in the first place and has the expansion joints cut into it.
If random cracks exist, and they usually do to some degree, contractors can apply an overlay after completing a few repairs. Steve Hitchcock, owner of Hitchcock Concrete Finishing located in Abington, Mass., has been in the decorative concrete business since 2005, and he follows several steps to repairing cracks before applying overlays. “I first v-cut or chase them, power wash, let dry and fill with epoxy,” Hitchcock says. “After it is dry, I’ll grind it flush, and then I’ll put a preliminary skim coat over the crack repairs before applying the first skim coat.”
After sealing the cracks, Osteen says you must broadcast a large grit silica on the surface because the acrylicly modified materials don’t have solvents in them. Without the proper solvents, the material won’t be able to chemically bond to the epoxy modified material, and it is important to have a good mechanical bond.
Crack repair won’t guarantee a crack-free end product. “The rule of thumb is if it has a crack there you’ve got a 60 to 70 percent chance of stopping that crack from re-appearing down the road,” Osteen says.
If contractors encounter a badly cracked concrete surface they can try to sell their customer on the idea of putting down an overlay that looks like flagstone, Osteen says. “You can incorporate the broken and cracked areas in the design,” he says. “This will minimize the appearance damage that is going to happen if you get a crack. If you put those cracks as part of your grout line design then even if it cracks a little bit you’re hardly going to notice it.”
Moisture from the ground up can create a bond failure, Hitchcock says. To prevent this, contractors can complete a Moisture Vapor Emission Rate (MVER) test. This is especially important when applying epoxies and urethanes because they are not a breathable coating, Anderson says. “You need to make sure you aren’t exceeding an MVER of 3 to 4 pounds. If an MVER is too high the overlay will peel off and fail,” he explains.
Another important step for contractors to take in surface prep is removing contaminates from the surface. One way to complete this step is acid washing. “You can turn around and spot check the deck for pH then wash it and coat it with an acrylic,” Osteen says. “We recommend acid washing all decks that are going to be coated with an acrylically modified material.”