We poured another couple of test pieces yesterday. We are trying to figure out the best way to handle the edge where the concrete meets the oak trim. If we were doing a regular concrete countertop this wouldn’t be a problem because there would be no oak trim. The countertops would be poured in a mold, unmolded, and then installed. We are doing our countertops poured in place. The oak trim serves as the form. We noticed in our first test pours that there is slight shrinkage as the concrete cures, and if it has been troweled level with the form, there is a slight depression between the concrete and the trim.
Yesterday I experimented with two methods for dealing with this shrinkage and getting the concrete edge to set up nicely against the edge. I am getting much better at troweling, and understanding how the concrete sets up. On both my pieces I had worked up the cream and smoothed it over. On my first piece, I had over troweled and ended up with a dull finish. On the second piece, I had stopped troweling earlier, and I found I had a hard, shiny shell as a result.
On the first piece, I tried to smooth the finish with 220 grit sand paper. It was a beautiful, matte finish. Then I tried wet sanding it with 240 grit sand paper. It was coming up nicely and then all of a sudden I had sandy grit on the surface. I had sanded through the cream and was into the aggregate. I hastily dried off the whole thing and hope for the best. I’m assuming it is going to be a rough surface on that one.
In terms of edge treatments, we have figured out that we need about 1/16″ extra concrete over the edge of the oak. This has to be shaped during the skreeding, and when it gets floated with the mag trowel. It is something that you just have to eyeball, so it is going to be a bit dicey. Oh, well. The good news is that the edge of the concrete is part of the material. It isn’t like the edge of a piece of plywood or doorskin. The finished edge of the concrete has a lovely feel of the hand that made it. Not manufactured.
We are definitely getting excited as we get closer to the full pour. We have decided to pour one counter a day, instead of trying to do them all in one day. We are going to be mixing small batches of concrete in a bucket with our electric drill. This way we can manage the materials and keep things fairly tidy.
Matt cut out the kitchen sink knockout yesterday. The bathroom counter should be finished today. The kitchen island is almost done, the base cabinets just need to be pinned to the island structure. With luck we will pour our first countertop tomorrow.