How to Lay Slate Tile on a Wood Subfloor

Slate tile is tough enough that you can forego the usual underlayment of cement board and lay it directly on your wood subfloor--with a few caveats. The tile has to be at least 1/2 inch thick (3/4 inch is better). The wood underlayment has to be at least 1 1/4 inch thick. Don't take this approach with a bathroom floor, as moisture and sitting water can get under the tiles and soften the wood subfloor, causing the tiles to crack.

Difficulty:

Moderate

Instructions

Things You'll Need

• One gallon of floor-grade polyurethane
• Lambswool floor-gloss applicator
• Tape measure
• Chalk snapline
• Thinset mortar
• Notched trowel
• Enough slate tile to cover the floor
• 1/8-inch plastic spacers
• Wetsaw
• Grout
• Rubber trowel
• Bucket
• Sponge
• Liquid grout sealer
• Small paintbrush

1. Sweep the subfloor thoroughly. Apply a layer of floor-grade polyurethane to it by pouring a line of it near the far corner of the room (furthest from the door) and dragging it toward you with your lampswool gloss applicator. Continue pouring and dragging until the entire floor is coated. Let the polyurethane dry overnight. This will prevent the wood from soaking up the moisture out of the mortar that you will use to install the tiles.

2. Use your tape measure and snap line across the center of the floor in both directions, so there are two intersecting lines dividing the room into four squares. Working one square at a time, from the middle of the room, spread down thinset mortar and press your tiles into place along the snaplines. Leave 1/8 inch of space between them, using your plastic spacers to keep it consistent. When all the full tiles have been laid, go back and lay the partial tiles, cutting them as needed with your wetsaw. Pull out all the spacers and let the tile set overnight.

3. Mix the grout with water in your bucket until it is the consistency of thick mud. Spread it onto the tiles with your rubber trowel, pressing it into the spaces between them and using the edge of the trowel to squeeze it off the tiles. Wipe down the surface with a damp sponge, taking the excess grout off the tiles but leaving it in the lines. Let the grout set for two days. Seal the grout lines with grout sealer, applying it with a small brush.

Tips & Warnings

• If you're flooring a bathroom, skip the polyurethane and lay a layer of 1/2-inch cement board over the subfloor before you tile.

• Wear eye protection when using your wetsaw.

References

• Installing Floor Tile
• Installing Slate Floors