This was a unique project we did for a restaurant in Durant, Oklahoma. It involved embedding glass into a precast countertop and then following it up with some concrete polishing. Making it all come together was quite a challenge. The business owner was looking for a concrete countertop with lots of personality and something customers would remember, we think we delivered just that. The first step of the process was making templates of the area. It was a fairly large project – over 125 square feet -so taking good measurements was critical. We hauled the templates over to the shop, laid them out on a casting table and started building the mold. Due to its size and layout we had to divide the countertop into ten separate pieces.
This client wanted to see red and clear glass chips on the surface of the countertops. Once we finished building the mold we randomly sprinkled the glass on the bottom then carefully filled the mold with cement. Precast concrete countertops are usually reversed, i.e., the top part of the countertop starts at the bottom of the mold. Once we pour and allow it to cure we break the mold open and flip the countertop exposing the top surface. We can then begin the concrete polishing process if sufficient time has passed.
How much time we have to wait mostly depends on the type of cement used (high early strength or just regular cement), temperature, and humidity. A high early strength cement mix that is curing in a warm shop with a high relative humidity can often be polished as soon as the next day. Regular cement mix in a cold shop with low humidity can take up to two weeks to harden sufficiently. If you try to polish green (soft) concrete, it only creates problems. Polishing actually removes material from the surface of the countertop, which is made up of stone, sand, and cement. Sand and stone are naturally hard materials but if the cement component of that mix is still soft it will be worn away much faster than the sand and stone creating an unlevel surface and actually ripping some of the stone and sand right off top leaving pockets behind. Not a pretty finish and since this project also included glass it was important to let the cement part of the concrete mix harden sufficiently before beginning so we could end up with a smooth surface.
After flipping the countertops we began the concrete polishing process using a variable speed grinder and diamond polishing pads. As the glass was now at the top but just below the surface of the countertop it was quickly exposed. We also exposed some of the stones that are part of the mix. How much is shown depends on how long you polish, more polishing exposes more stone and glass. We wrapped up by applying a sealer coat on it and loaded the sections into the truck for the two-hour trip up to Oklahoma. A lot of work but the final result speaks for itself.