I casted my own countertops from concrete. Its pretty easy if once you know
the steps involved. I highly recommend the book mentioned in the previous
post. I did mine before the book was published, and was suprised at how
similar my method was.
In general, make a template of your countertop and transfer it upside down on
melamine coated particle board or plywood.
Build 2" walls of wood to create a mold. Try not to go much thinner than that
as it may be prone to cracking. Caulk and fingersmooth all the edges that you
want to be rounded over. Reinforce with rebar and or some sort of wire mesh
(ideally the 6 " grid type). Wire all the reinforcement into one rigid
structure and suspend it about an inch off the bottom. Wipe on old cooking oil
as a release agent,
Mix 5000 psi concrete with as little water as you can while still having it
workable. This ensures a stronger slab. Dump it in the mold, pack it in well
in all the tight spots , screed the top with a striaght edge and let it cure.
No need to trowel or float to a smooth finish since its the bottom anyway.
once it turns hard, you might want to cover it with a tarp to retard
evaporation since keeping the water in the slab ensures it will be as strong as
possible. I kept the slab wrapped for weeks for a granite hardness
Once you release it from the mold you will no doubt have countless air bubble
holes on the finished side. Simply wet the slab down with water and fill the
holes with portland cement, water and some acrylic admixture. Add some
concrete pigment in the mixture for a nice patina. once cured, sand the whole
surface and further round the edged by sanding.
The holes where the faucet pokes through are made of dowel or pvc sections.
Wrap them once around with 1/8 inch packing foam sheet so that they will pop
out without effort. Sink cutouts are molded right in. My sink is undermounted
for the coolest results. It was actually an overmount sink that I mounted
underneath since I was too cheap to buy a new sink. No need to attach it to
the countertop, just suspend it level with the cabinet and lay the countertop
over it. A bead of caulk or silicone seals the seam.
Seal it with 3 coats penetrating masonry sealer, and polish the surface with
neutral color Kiwi shoe polish. The surface will shine like glass and resist
water and stains.
You really should do a small test slab to get a sense of the color and get
experience working the material.
I struck a test piece full force with a hammer blow and barely chipped the
concrete. If you form the slab properly, it will be nearly indestrutabe and
crack free for the life of the countertop.