More Concrete Counters

Once again, I am posting about another project that I am working on instead of my house. I am making a concrete countertop to go in Dermott's pantry. Eventually I will be making concrete countertops for my house, so this can be considered practice (sorry Dermott!). Most of the kitchen is decked out in a beautiful dark green granite, so I would like to tie the concrete into that look somehow. The main kitchen counter runs along the east wall of the house, then there is a small partition wall that separates the pantry. My plan is to use a small piece of the granite on the pantry countertop were it butts into the partition wall, as if the countertop continued from the kitchen. I will break the other edge of the granite and pour the piece into the countertop casting. It whole piece should have a seamless polished top, with the granite gracefully fading into the concrete. It is an L shaped counter, and the miter will be decorated with an inlayed brass strip.

My SketchUp model

Dermott rendered my model to make it more realistic looking.
Notice the Granite on the leading edge.

As noted in an earlier post, I took a two day workshop with Stone Soup Concrete at the Yestermorrow School back in December. Two days is enough to give you a taste of the craft, but there is so much more to learn! I have been spending my days reading up on the trade, sourcing materials and devising experiments. 

There are several challenges that I am experiencing. First, I need to produce a color that is compatible with the green granite. The color we made at the workshop was a slate gray that would probably look great against the granite on its own, but I would like to work some green into it is possible. To color the concrete, you can use pre-made color mixes which tend to be very expensive and never quite right, or you can mix your own using raw pigments. The pigments are the same that are used for making oil paints. I am using combinations of red, blue, green, yellow, white and black. Some of these are for this countertop, others are just for my records to be used on other projects. Yesterday I mixed up my first batch of tests to try to get a handle on the colors. I am making ten different 4" x 4" x 3/4" tiles.

Pigments weighed out ready to be mixed with concrete

Corwin helped make the samples

I really enjoyed this process because it allowed my scientific side to come out. A small amount of pigment has a huge effect on the color of the concrete, and the pigment is expensive so I was making small samples. This means that often times I would be weighing out less than a half of a gram of each pigment. It was almost like being back in chemistry class. If anyone would like more info on the color formulas or sources for pigments, I would be happy to send along what I learned. Just send me an email.

Once mixed, the samples are plopped in the form and vibrated using a sophisticated mechanical agitation system to work the air bubbles out...

These samples will now have to sit for five days before I can remove them from the forms. Since these are so small, I could remove them after 24 hours, but the 544 pound countertop will definitely need the full five days and the length of time the concrete sits in the form affects the color. Oh well, it is good to practice patients.

I already have several other test lined up to experiment with inlaying metal and stone into the surface, and various methods to form the sides and bullnose profile on the front edge. It seems that I will have several coffee table tops after the experiments are done.