When tiling over plywood, you should always put down a layer of cement backer board first, which will provide the necessary support for the tile. Here are eight important steps to keep in mind when installing cement backer board:
- Check the plywood subfloor for any movement and squeaks. Use 2 inch drywall screws to fasten down any trouble spots, driving the screws through the plywood and into the floor joists below.
- Use a notched trowel to spread thin-set mortar over the plywood subfloor.
- Lay the cement backer board into the thin-mortar, making sure to overlap any seams in the plywood subfloor by at least 4 inches.
- Fasten the backer board using an impact driver and backer board screws; space the screws 4 inches apart around the perimeter of the backer board sheet and 8 inches apart across the center.
- Leave a one-eighth inch gap between the backer board sheets and stagger the sheets so that four corners don’t meet at a single intersection.
- Cover the seams between the backer board sheets with fiberglass mesh tape.
- Spread a thin layer of thin-set mortar over the taped joints.
- Once the mortared joints have cured, you can start setting the tile.