Directions to Install Terrazzo

A Terrazzo Floor

Terrazzo floors are attractive, wear-resistant and require a minimum of maintenance. Installing a terrazzo floor can be easy or difficult, depending upon the quality of preparation and the tools and materials selected to do the job. Two step-by-step methods are given below, the first for installation over an existing concrete floor, the other for installation over an existing wood floor. The final appearance will be the same for both methods.

Things You'll Need

• Portland cement
• Aggregate
• Sand (optional in most instances; see text for details)
• Large wheelbarrow or small rental cement mixer
• Small rental roller for concrete
• Tap water
• Large flat board to level the cement mix
• Tape measure
• Carpenter's level
• Roll-on waterproof membrane product (if installing over wood)

Instructions

Installing a Terrazzo Floor over an Existing Concrete Floor

1. Remove any materials sticking up from the cement floor: screws, nailers, etc. Grind down any protrusions. Thoroughly clean the floor so that unwanted materials don't float up into the fresh cement.

2. Apply Portland cement to the surface, at least 2 inches deep. You can buy Portland cement at any large home-improvement store. Before beginning to mix, calculate how much cement you will need. One bag of cement will make a about 25 square feet of 2-inch-thick concrete. Always mix at least 10 percent more concrete than you think you'll need. You can add a colorant to the cement when you mix it.

3. Mix the cement and water in a large wheelbarrow or a small cement mixer, two to three parts water to one part cement to achieve a substance that is thicker than food batter, but not too thick to pour.

4. Pour the cement mix onto the floor and spread it evenly with the edge of a flat board.

5. Purchase an aggregate or make it yourself from marble, glass and/or plastic fragments. Traditional terrazzo commonly uses marble chips, which you can buy at lumber yards or home improvement centers, If you make the aggregate yourself, always wear safety goggles and heavy leather gloves. Traditional terrazzo uses about 70 percent aggregate to 30 percent cement mix. If the ratio of aggregate to cement drops far below 70/30, add 10-15 percent sand.

6. Distribute the aggregate evenly over the surface of the wet cement. Flatten the floor further after a couple of hours, using a small cement roller. The floor should now set for at least five days before grinding it flat for use.

7. Finish your floor with a terrazzo grinder. These can be rented, with a diamond grinder being the preferred choice. Once you have achieved an even matte finish, continue working on the floor with a concrete polishing machine, also available as a rental. A very high gloss is achievable.

Installing a Terrazzo Floor over a Wood Subfloor

1. Assess the wood subfloor and underlying floor joists. Will the floor-system support the weight of the terrazzo floor described in Section 1 above? If not, another kind of terrazzo floor called a thin-set epoxy terrazzo floor system can still be constructed, but that is beyond the scope of this article. If the existing floor system is robust and will support the weight of the terrazzo, then proceed to Step 2.

2. Waterproof the area where the terrazzo will be installed; failing to do this will result in deterioration of the existing subfloor. Any of the membranes commonly used under tile floors will work. Roll-on membranes are easy to install and available at home improvement centers. There are also two-step systems available; the first step is an adhesive and the second step is a cement-like membrane material. The adhesive provides an additional bond between the cement-like membrane and the wood subfloor. For larger floors, or where some flexing is anticipated, the two-step system is a good choice; otherwise the one-step roll-on membrane is relatively inexpensive, quickly installed and will provide adequate isolation of the floor from moisture.

3. Once the waterproof membrane has dried, follow Steps 2 through 7 of the procedure above (Installing a Terrazzo Floor over an Existing Concrete Floor).

Tips & Warnings

• Unless your terrazzo floor is quite small, it's better to divide it into four- or two-foot squares. This reduces the likelihood of large-scale cracking. Aluminum, brass or teak strips are often used to separate the squares. Even so, most terrazzo floors (like most concrete floors) will eventually crack, but if the cracks are contained within a grid they will be minor and easily repaired. With a terrazzo floor, once the crack has been grouted and sealed it is nearly invisible.

• Aggregate can be a commercial product made from marble chips, a commercial "green" product made from a variety of recycled materials or an aggregate that you make yourself from the materials described.

• Always wear safety goggles and a mask when grinding terrazzo. Sweep up and bag the residue frequently. Use leather gloves throughout the entire process; handling cement quickly dries your skin. Ventilate your work area well.

• Temperatures of 40-60 degrees are ideal for curing concrete. When it is hotter, putting damp cloths over the curing terrazzo (and keeping them damp for several days) will ensure high-quality concrete.

References

• Concrete Basics
• Design Considerations for Terrazzo (PDF)

Resources

• Terrazzo Floors