Casting Cement
Date: Wed, 12 Mar 2003 09:41:19 -0500
From: Jeremy Bergsman
Subject: Concrete mills and Re: Increasing Bitterness

Ive been researching the art of making "decorative" concrete for a kitchen
countertop. Ive learned a couple things that may be useful for those
making concrete roller mills so I thought Id post them.

First, concrete is a great casting material. I had visions of these rough
rollers looking like concrete on the sidewalk, with bits chipping off into
the grain. In fact, in an appropriate mold, concrete can be as smooth as
glass. One could easily add material to the inside of the mold to cast
grooves into the rollers. Vibrating the mold as you add the concrete helps
get the bubbles out and get the fine cement around the sand and aggregate to
make a smooth surface. A typical technique is holding a recipricating saw
without a blade against the mold and running it a few minutes.

Second, one can make concrete a lot stronger with a little know-how
(decorative concrete is actually stronger than "regular" concrete). The two
tricks are 1) use more cement and 2) use less water. You can buy cement
rich blends like Quickcrete 5000, and some of the special mixes previously
mentioned here or "Precision grout" mixes are also supposed to be good. To
use less water the big trick is to add a water reducer/plasticizer which
helps the concrete flow better with the reduced water. Then mix up the
concrete with as little water as possible. If you want to mix your own, a
recipe for 1 cubic foot is: 24 lbs cement, 1 cubic foot of sand and gravel,
and 1+ gallon of water, plus the admixtures as suggested by the manufacturer
(will be a couple ounces).
Casting Cement