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Installing a Cement Backerboard


You may be tempted to rush ahead and get to the fun part, laying the tiles, but resist the urge. Unless you prepare the surface under the tiles properly, you'll end up having to retile a lot sooner than you want.


Tiles need a smooth, flat, rigid surface to sit on. Plywood is sometimes used, but cement backer board is generally considered a better choice. Backerboard is essentially a thin layer of concrete with fiberglass mesh on both sides. It was designed specifically as a setting surface for tile.


Backerboard comes in a range of sizes: 3x5-foot sheets are most common for floors. Over a 5/8-inch subfloor, use 1/4-inch-thick sheets.





Step 1: Snap a grid of chalk lines on the floor to mark the dimensions of the sheets

Mark the dimensions of the sheet Plan so that joints in the backer board won't line up with joints in the subfloor. With the smooth side of a ¼-inch notched trowel, spread enough adhesive for one sheet. Ridge the adhesive with the notched side of the trowel.

Step 2: While the adhesive is still wet, place a sheet of backer board onto it

Place a sheet of backer board Leave a ¼-inch gap between the backer board and the wall and a 1/8-inch gap between the backer board sheets. Position the sheets so that you don't have four corners meeting.

Step 3: After you've you have positioned each sheet, drive backer board screws into it every 6 to 8 inches

Drive backer board screws After you have positioned each sheet, drive backer board screws into it every 6-8 inches. Around the perimeter, position the screws at least ½-inch but no more than 2 inches from the edge.

Step 4: With a margin trowel or the flat side of your notched trowel, fill the joints with adhesive, smoothing it so it extends about 1 ½ inches on each side of the joint

Fill the joints with adhesive The extra adhesive makes it easier to bed the tape

Step 5: Cover the adhesive-filled joints with 2-inch vinyl-coated fiberglass tape, pushing it firmly into the adhesive

Cover the adhesive with  vinyl-coated fiberglass tape You can cut the tape to length with the thin side of your trowel. When the tape is embedded, scrape off any excess adhesive from both sides.

Step 6: Cover each length of tape with a thin layer of adhesive

Cover the tape with adhesive Spread the adhesive with the flat side of your trowel and feather the edges. You want the transition from board to board to be as smooth as possible.