Installing a Cement Backerboard


The key to a solid foundation under your tile floor begins with cement backerboard

For a tile floor that lasts for years without cracking, a cement backerboard is crucial.

Backerboard is a thin layer of concrete with fiberglass mesh on both sides. It is available in a range of sizes, but 3 x 5-foot sheets are most common.

This project guide shows how to properly lay out your backerboard with a chalk line and using mortar to secure and level your floor before installing tile.

Tip: Do not install new tiles over existing tiles or over a wood or plywood floor.


Snap a grid of chalk lines to mark the location of backerboard
chalk lines mark location - Installing Cement Backerboard

• Plan so the joints in the backerboard won’t line up with the joints in the subfloor.
• With the smooth side of the ¼-inch notched trowel, spread enough mortar for one sheet.
• Ridge the mortar with the notched side of the trowel.

While the mortar is still wet, place a sheet of backerboard onto it
Place a sheet backerboard - Installing Cement Backerboard

• Leave a ¼-inch gap between the backerboard and the wall and a 1/8-inch gap between the backerboard sheets.
• Position the sheets so you don’t have four corners that meet.

Secure backerboard with screws
Secure backerboard with screws - Installing Cement Backerboard

• Drive screws every 6-8 inches once the backerboard is in position.
• Around the perimeter, position the screws no more than 2 inches from the edge, but at least ½ inch in.

Fill the joints with mortar
Fill joints with mortar - Installing Cement Backerboard

• Use the flat side of your notched trowel to smooth the mortar so it extends about 1 ½ inches on each side of the joint.
• The extra mortar makes it easier to bed the fiberglass tape.

Cover joints with fiberglass tape
Cover joints fiberglass tape - Installing Cement Backerboard

• Cut the tape to length with the thin side of your trowel.
• Push the fiberglass tape into the mortar.
• When the tape is embedded, scrape off any excess mortar from both sides.

Cover each length of tape with a thin layer of mortar
Cover each length tape - Installing Cement Backerboard

• Spread the mortar with the flat side of your trowel and feather the edges.
• Transition from board to board so it is as smooth as possible.