How to Install Backer Board in the Floor Before Laying Tile

Achieve the Ideal Flat Surface for Installing Floor Tiles with Backer Board

Construction site
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Floor tiles should be installed over smooth, flat surfaces. In order to achieve the ideal flat surface, most contractors rely on backer board. Cement backer board is a thin layer of concrete designed to be setting surface upon which tile can be installed. Backer board comes in different sizes and you will pick the right one depending on the type of floor you are installing.

Tools for Backer Board Installation

When you are going to install backer board as a floor setting surface, you will need the following tools:

  • 1/4 trowel
  • Electric drill
  • Backer board
  • Screws
  • Chalk line
  • Fiberglass tape or Alkali resistant tape
  • Adhesive

Once you have your materials and tools, you'll complete the following steps to install your backer board.

1. Design Your Layout

Use a chalk line to mark the dimension of the backer board sheets onto the floor. Remember that it is best when joints in the backer board are not aligned with the joints in the subfloor. Using the trowel, spread adhesive and ridge it with the notched side of the trowel. Next, place a sheet of backer board over wet adhesive. Remember that the wall gap shall be about ¼ inch with 1/8 inch between backer board sheets. The purpose of the thin set is to eliminate voids beneath your backer board. The backer board will not expand, but walls will and if you butt joint the installation, the floor might pop out. Install the backer board in such way that you won’t have four corners meeting at one single place.

By staggering the joints, you will increase the substrate toughness by reducing your weak points. Apply thin set just one row at a time so you can replace and reinstall them faster and easier.​

2. Install Screw and Joints

Once you have placed all backer board sheets, install screws every 6 to 8 inches although every backer board following the manufacturer’s recommendation.

Do not use drywall screws as they are not recommended to be used to hold the backer board in place. All of your backer board pieces should be cut before they are placed over the floor. Along the perimeter, screws should be installed at least ½ inch from the edge, but no more than 2¼ inches.

You will want to go and check every seam. Double the screws in those areas just to be sure it is attached properly. Using the flat side of the trowel, fill the joints with adhesive, smoothing it so the adhesive extends at least 2 inches on each side of the joint. The tape will be easier to install with this extra adhesive. Start your screws in the center of the board and work out. It is important to highlight that screws shall not be installed all the way down to the floor joists.

3. Install Tape

Using the vinyl coated fiberglass tape, cover the joints that have adhesive from the previous step. Cut the tape to your required length. Once the tape is in place, remove any excess adhesive from both sides of the tape. Spread adhesive over the length of the tape using the flat side of the trowel. Do not add a lot of adhesive as you will want your transition to be really smooth. It is recommended if you can get alkali resistant tape so it will not break down as a result of the chemicals present in most thin sets.