Being a GFRC supplier, Ralston didn't have any problems getting his materials for the Bosch showroom job. For him, the challenges came in the size of the pieces he was creating. The pieces were so large that Ralston went out and purchased a special pump to spray the GFRC mixes. "The challenge you run into is once you get to a certain size, you can't get the GFRC mix into the mold fast enough by hand before it begins to set," he says. The pump allowed him to spray the mix into the mold much faster.
And once the pieces were complete, Ralston had to figure out how to get them through the doorway of the building. Special carts were made for wheeling the GFRC creations in, and then the pieces were set into place.
When looking at a GFRC countertop most people won't be able to see a difference from regular wet cast countertops. But the process behind creating the GFRC countertop is quite different, Ralston says. For the GFRC mix, Ralston uses a one-to-one cement and silica sand ratio. He also adds water, a curing agent, admixtures and any colors needed.
Ralston, who teaches a GFRC training class for Cheng Design, tells contractors that GFRC can be mixed with a hand drill, mixing paddle and a 5-gallon bucket. However, unlike regular wet cast mixing, GFRC needs to be mixed in a shorter time period. "With GFRC we have such a high cement content that it has to be mixed quickly. Typically I mix within 5 to 7 minutes," Ralston says.
To be sure he mixes fast enough Ralston often uses a Collomix hand mixer. Once the mix is ready, Ralston uses a drywall hopper to spray the face coat onto the mold or pours a self-leveling mix straight into the mold.
The next step is to mix the back coat, which includes the AR glass. This gets mixed in the same fashion as the face coat, using the same tools, to make sure the AR glass is distributed throughout the entire back coat. But take caution. "When the fiber glass is added at the very end you don't want to over mix because the blades on the mixer begin to destroy the glass fibers," Ralston says. "You want to get in and mix it for about one minute."
If you prefer a self-leveling mix for horizontal concrete, Ralston says to add a self-consolidating concrete (SCC) admixture to the mix, normally the back coat. "The SCC tricks the concrete into believing it has more water then it does. It makes it so fluid that when poured out it will find its own level. At some point the switch turns and the concrete reverts back to its original water content in the cement," Ralston says.
Both the face and the back coat can be vibrated whether using a self-leveling or regular GFRC mix. A little vibrating can help achieve a level horizontal surface but is not necessary. When Ralston wants to vibrate one or both coats he hooks a vibrator to his table, turns it on and then sprays or pours the GFRC mix while the table is vibrating.
Although Ralston says most concrete countertop contractors have all the tools they will need for creating glass fiber reinforced concrete countertops, he admits that GFRC may not be the easiest material to work with. So before jumping into GFRC countertops, he suggests contractors get some training. "If you're a contractor just getting into it, training is the key that's going to save you thousands of dollars in the learning curve," he says. Often times, Ralston says the GFRC process really clicks with people after they've seen it done in person.