Pouring a concrete counter

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:
P1030807.JPG

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:

P1030831.JPG

Then we flip it and create the general mold:

P1030836.JPG

Here you can see the bottom lip and top splash (all inverted for the pour):

P1030840.JPG

Then we start doing the finer details like the basin:

P1030842.JPG

And where the faucet and drain will go:

P1030873.JPG

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:

P1030881.JPG

P1030878.JPG

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?!

P1030891.JPG

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.

P1030885.JPG

Coloring:

P1030890.JPG

Fibers:

P1030887.JPG

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.

P1030896.JPG

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:

P1030902.JPG

Then we packed it all into the mold. First we lay the stronger colored lines:

P1030904.JPG

Then we packed the rest of the cement around it:

P1030906.JPG

And we packed some more:

P1030908.JPG

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:

P1030909.JPG

And then pack some more:

P1030910.JPG

Until finally it looks like this:
P1030913.JPG

We covered it with plastic to keep the humidity in so that it cures slowly:
P1030916.JPG

And every once in a while we sprayed some water to keep it humid:
P1030920.JPG

After four days of letting it cure we broke the counter out of the mold:
P1040014.JPG

We then started the process of sanding it down. First you get the rough edges off:

P1040036.JPG

Then you sand it with rough sand paper and water:

P1040027.JPG

Then you pass a slurry of concrete and color over it. This fills in any air holes:

P1040085.JPG

Once the slurry is dried you sand it some more. The result is a two layered look:

P1040099.JPG

To get any fibers that may have been exposed through sanding you torch the cement;

P1040102.JPG

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:

P1040143.JPG

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.

P1040140.JPG

About the author: Gennaro Brooks-Church

Leave a Reply

Your email address will not be published.