We make concrete counters for bathrooms and kitchens. Concrete is gotten locally and can be mixed with recycled aggregates like glass or stones. And especially if you make them on site we feel it is a very green alternative.
Other marble counters consume a lot in extraction and transport. And there really isn’t anything more locally harvested than on the job site itself.
Here is a counter we are building for a bathroom in the Brooklyn Green Show House.
The first thing is to make the mold.
First we create the frame where the counter will sit:
Then we create an upside down mold out of something flat. Here it is wheat board that we salvaged. We reinforce the frame from below:
Then we flip it and create the general mold:
Here you can see the bottom lip and top splash (all inverted for the pour):
Then we start doing the finer details like the basin:
And where the faucet and drain will go:
Meanwhile another worker is preparing the aggregate. In this pour we are using salvaged glass that was being thrown out. We break it into smaller pieces:
Meanwhile we prep the inverted mold with Pam grease so that the concrete won’t stick to the wood. This is the only thing we would ever use Pam for. Who eats with that crap?!
And we mix the concrete. This mix has the following:
white sand, white Portland cement, fly ash, marble dust, broken glass. We also add coloring, cement glue and strengthening fibers.
We mix it so that it is a very thick mix. Not watery at all. The least amount of water but still manageable. Meanwhile we als apply a mesh in the mold for extra strength.
We wanted two colored lines in the counter so we mixed a small batch with extra color and some diamond dust to make it sparkle. This little mix will be laid in three lines along the counter to make a marbled effect. Mixing it with the diamond dust:
Then we packed it all into the mold. First we lay the stronger colored lines:
Then we packed the rest of the cement around it:
And we packed some more:
We banged and packed and packed some more until the water started to come out of the mix. We do this to get rid of any air bubles caught on the counter.
We lay the mesh over it:
And then pack some more:
Until finally it looks like this:
We covered it with plastic to keep the humidity in so that it cures slowly:
And every once in a while we sprayed some water to keep it humid:
After four days of letting it cure we broke the counter out of the mold:
We then started the process of sanding it down. First you get the rough edges off:
Then you sand it with rough sand paper and water:
Then you pass a slurry of concrete and color over it. This fills in any air holes:
Once the slurry is dried you sand it some more. The result is a two layered look:
To get any fibers that may have been exposed through sanding you torch the cement;
And then you do the final sanding where you go from rough to extra fine. You use diamond pad sanders on a grinder with water. Then you touch up any spots by hand:
The end result is something that doesn’t quite look like cement but it doesn’t look like marble either. The next steps, which we haven’t gotten to is to seal and wax it so that it really shines….that is for another post.
There is a reason concrete counter tops are so costly. It takes a tremendous amount of work. The materials are cheap but the labor is extensive. This combo of cheap materials and lots of labor is a Build It Forward strategy.