Terrazzo is concrete mixed with marble chips. It is poured onto an existing concrete slab and then polished to a glossy shine for flooring. Laying terrazzo requires several steps, and you will need to rent a stone floor grinder. The process may seem complicated, but a dedicated and experienced do-it-yourself homeowner can lay a terrazzo floor with a little patience and persistence. Take your time and carefully, follow these steps to laying your new, beautiful floor.
Cut 1-inch grooves, or "control joints," into the concrete slab base to prevent the terrazzo from cracking through the top layer (which would show on the surface of the floor). Use a circular saw with a masonry blade to make control joints that are about 3/8 inch thick and 1 inch deep. Cut the joints diagonally across the surface of the floor, about 3 feet apart.
Clean concrete slab thoroughly by sweeping and then power washing. Finally, scrub with a solution of 3 tablespoons muriatic acid to one gallon of water. Rinse well with the power washer.
Apply zinc dividers by cementing them to the concrete slab. Place the zinc dividers in 3-foot grid. Fasten strips of plywood to the perimeter of the floor to keep the terrazzo from overflowing the surface area of the floor.
Mix and Pour the Terrazzo Mixture
Mix the terrazzo flooring material in the following proportions: use 200 lbs. of marble chips for every 94-pound bag of Portland cement, (which acts as a concrete binder to the marble chips). Add the amount of water recommended by the manufacturer of the Portland cement and mix well. Use a wheelbarrow to mix small batches or rent a cement mixer to mix a larger amount.
Pour the terrazzo mix onto the concrete slab one wheelbarrow at a time and immediately roll over the mix with a heavy roller.
Use the concrete trowel to further push the marble chips into the wet concrete binder. Your aim is to create an almost solid mass of marble glued together with the concrete binder.
Scatter additional chips. Once the entire floor has been poured, rolled and worked with the trowel, scatter additional marble chips on the floor's surface. Scatter the marble chips generously by the handful. The surface of the floor should be covered in loose marble chips.
Roll over the entire surface of the floor with the floor roller. This step compresses the mixture and forces out any air bubbles.
Allow the cement to cure for two days.
Grind, Polish and Finish the Floor's Surface
Start the floor grinder. After curing, go over the floor with an electric floor grinder for stones. Begin with the coarsest grinding stones and make several passes. Then change to medium-fine polishing stones for a few passes and then fine grade ones. When the floor shows the shine of the marble and the zinc-border strips, you only need to polish to the shine you desire.
Hose the grinding dust off of the floor. If you observe tiny pinholes in the concrete, these are caused by air bubbles that were not squeezed out with the heavy roller. These are dealt with below.
Mix and pour a thin "slurry" of quick-set Portland cement over the entire surface of the polished floor. A "slurry" of cement is cement powder mixed with water until it is the consistency of ketchup. This will fill in the tiny air bubbles.
Work on a small area of the floor at a time, use a concrete trowel to remove the slurry from the surface of the floor, leaving only what fills in the tiny pinholes.
Make a couple more passes with the grinder fitted with fine grinding stones until the surface is gleaming and shiny.