Contractors can complete this test by using a pH paper and bottled water or a pH sensitive pencil.
“Acrylically modified materials have one weakness in their bond characteristics — that the material only works on a bond of a pH that runs a couple of points above and below 7,” Osteen says. “If the deck is too acid or too alkali the material’s reaction to the pH causes the acrylic to polymerize too fast, and it doesn’t get penetration into the concrete.” A poor pH reading will result in pop-offs and bond failures. “Whether the pH of a deck is too high or too low, when you acid wash it and neutralize the acid you’re going to bring the concrete to a 7 no matter what,” Osteen says.
After acid washing, the deck should then be pressure washed. Hitchcock suggests pressure washing with at least 3,000 psi of pressure and a rotary nozzle to open the concrete pores.
If contractors are unfamiliar with checking the pH and acid washing, they may encounter problems if not completed correctly. To avoid this, an alternative is mechanically prepping the surface.
This prep scarifies, or abrades, the surface allowing the overlay to securely attach to the base, explains Dan Whitaker, the Northeast representative for Butterfield Color. “You are removing any sealers, any weak concrete and anything off of the surface,” Whitaker says.
Osteen notes contractors must be aware of the age of the concrete. “We have to be concerned if you’re dealing with new concrete,” he says. “You have to know if any cure and seal compounds were used on the concrete.”
One way for contractors to determine the condition of the concrete surface is by throwing water droplets onto the concrete. “If they aren’t immediately absorbed by the concrete there is some kind of cure on it,” Osteen says. “If water’s not going to penetrate into it easily then you’re going to have a problem sticking to it.”
Acid washing will not remove a cure and seal, but scarifying will.
Applying an overlay
As soon as the surface prep is complete, contractors can apply the overlay. “As long as the surface is dried, cured and clean I will start the process,” Hitchcock says. “Drying conditions can vary, but usually 24 hours is sufficient.”
There are several conditions contractors must be aware of before beginning the application process. They must have experience with the product they are using, mix materials as accurately as possible, and be prepared with enough materials and tools, Anderson says. It is also essential to apply the overlay in workable temperature conditions.
Hitchcock recognizes the effect conditions can have on the process of application. In humid conditions he uses fans to move the air. “When skim coating you need to prime the surface more because the concrete will suck the moisture out of the mix and make troweling more difficult,” he says.
Before applying the overlay, contractors must determine if they want to apply a scratch coat. “A lot of times scratch coats are put down because we want to incorporate a certain color grout line in the design,” Osteen says. “In that case, we would pigment all of the material we are going to scratch coat on the deck.” The scratch coat is a thin layer of material that is put down for color, Osteen says.
The surface must be primed after the prep has been completed, Whitaker says. Next, gauge the material down to the desired thickness, and then close up the gauged material with a trowel.
Overlay thickness can vary depending upon the specifications of the architect, recommendations of the manufacturer, experience, and what you know your materials can do and how they perform, Anderson says.
Whitaker says the stamp pattern, the texture and the grout lines will also determine the thickness of the overlay. According to Whitaker, stampables are typically done about ¼ to ½ inch thick.
Next, after the surface of the material has lost its sheen contractors can apply the release agent and begin stamping. “The final steps would be detailing the area, taking care of any squeeze that may have come up between the stamps, then antiquing or staining depending upon the type of look you are going for,” Whitaker says.