Polished concrete is a durable material that is increasing in popularity, whether it is used for floors, counter tops or tiles. Large surfaces like floors are usually polished with heavy machines that can be rented. Smaller projects can be polished with an ordinary electric sander or a hand-sander. A polished concrete tile is a good first project.
Choose the best concrete mix for your project. Use a prepared sand concrete mix, or mix 1 part cement, 2 parts sand, and one-half part water. If you want to use pigment in a bright or vivid color, use white cement and pale or white sand.
Use a jigsaw to cut the cement board into the same shape as the bottom of the mold, but a little smaller. Place the board inside the mold. You should have about a one-inch gap all around the board. Cement board stiffens and supports the tile, making it possible to pour the concrete as thin as 1 inch.
Spray the cement board to dampen it slightly. Mix the concrete according to package directions. Pour it into the mold a little at a time. Stop several times and tap the edge of the mold with a hammer to release air bubbles.
Drag the 2x4 board across the top of the mold from one side to the other to level the concrete. As you drag, jiggle the board back and forth slightly. This will help compress the wet concrete. If there are low spots, toss some of the excess concrete in them and level again.
Without waiting for the concrete to dry, place the inlays on the surface of the concrete mix. Glass pieces, mother-of-pearl bits, or even attractive gravel all make good inlays.
When the surface water has evaporated, use a hand float or trowel to smooth the surface. Embed the inlays by troweling over them until they are covered with the cream of cement and find sand that is on the surface of the concrete.
Use a putty knife to shape and smooth the edges of the tile.
Place a polyurethane sheet over the mold to hold in moisture. Leave the concrete in the form in a warm, dry spot for at least three days. Mist the surface periodically to keep it damp.
Concrete is usually ready to polish after three days. If sanding ejects whole pieces of sand or inlay, wait another 24 hours to polish the concrete. Sand the concrete with wet/dry sandpaper or diamond pads. You can use an electric hand-sander or a conventional hand-sander. Start with a 100-grit or 120-grit abrasive and sand the entire surface of the tile.
Wipe the tile occasionally with a damp sponge to remove the slurry made by the sanding and to keep the concrete slightly damp. Switch to a 220-grit abrasive and repeat. Finish by sanding with a 400-grit abrasive. If you like the way the concrete looks, stop sanding. If not, sand a little more until you have the look you want.
Let the concrete dry for several more days. Brush on a concrete sealer and let it dry completely before you use the tile. It will continue to harden for 28 days after pouring.
If the concrete tile has any small gaps that you don't like, fill them with a paste of cement and water. Let the mix harden for several days and polish the surface. Wear rubber gloves when you work with concrete.
Wear a disposable respirator when you mix dry pigment. If you get wet concrete on your skin, wash it off promptly.