How to Install Underlayment Under Ceramic Tile

Ceramic tile seems hard as rock, but it's actually quite fragile if it isn't laid properly. The most important issue is stability. If the underlayment has any "give'' to it, or if it softens over time, that movement will eventually crack the tiles. Cement board is the preferred underlayment for ceramic tile today, because it cuts and installs as easily as drywall but is as solid as a sheet of cement once in place. Getting the cement board properly installed first will make the rest of your project go a lot faster and last a lot longer.

Things You'll Need

• 1/2-inch cement board, enough sheets to cover the floor
• Thinset mortar
• Mortar trowel with notches along one side
• 1/2-inch cement board
• Screw gun
• Galvanized drywall screws (1 1/2 inch)
• Jigsaw
• Mesh drywall tape

Instructions

1. Set your first sheet of cement board down in one corner of the floor. Mark around the edge of it with your pencil. Remove the cement board.

2. Spread thinset mortar over the whole area that will be covered by the first cement board sheet, based on the pencil mark. Scrape the mortar over the area with the notched side of the trowel, to put lines in it.

3. Set the sheet of cement board back in place. Screw it down with your screw gun and galvanized drywall screws. Sink the screws every six to ten inches throughout the board, making sure to bury the heads just below the surface.

4. Lay your next sheets of cement board in the same manner, putting them down in staggered rows, so there are no four-way intersections. Cut the end boards as needed with your jigsaw.

5. Lay mesh drywall tape over each of the seams between the sheets of cement board. Spread thinset mortar over the taped seams, using the flat (non-notched) side of the trowel. Get the mortar very flat and smooth. Let it set for 24 hours. The underlayment is now ready for tiling.

Tips & Warnings

• Wear eye protection when cutting cement board with a jigsaw.

References

• Installing Cement Backer Board