Installing Tile Backer Board Subfloor

tile floor

The first step in tiling a floor is installing concrete backer board. Concrete board is made from concrete on the inside and covered with a fiber mesh to give it strength. It provides a solid, stable, water resistant underlayment for the tile or stone floor and improves the bond of the tile or stone to the floor. The two main manufactures of concrete board are Durock and James Hardi. This article teaches you everything you need to know about installing concrete / cement board on floors. To learn how to install concrete board on walls read the article How To Install Concrete Board On Shower Walls.

Concrete backer board is sometimes called cement backer board.

brief how to

In this article, you will find information about:

  1. Layout The Pattern
  2. How To Cut Concrete Board, Hardi board, Durock
  3. Apply Mortar Or Adhesive To The Floor
  4. How To Lay Down Concrete Board
  5. Fastening The Concrete Board
  6. Sealing The Joints
  7. Set The Tile

tools and materials

  • tools and materials
  • concrete backer board
  • utility knife and extra blades
  • tape measure
  • pencil
  • 1 1/4" Durock tile backer screws or 1 1/2" hot-dipped galvanized roofing nails
  • Alkali resistant tape specified by the manufacturer
  • Type 1 organic adhesive or latex modified thin set mortar suitable for bonding cement board

Step 1 Layout The Pattern

Before cutting and installing the backer board you should figure out the layout of the cement backer board on the floor. Try to put any cuts along walls and let the factory edges butt up against each other in the field.

step 2 How To Cut Concrete Board, Hardi board, Durock

Cutting concrete board is quite easy. Simply use a utility knife and score one side of the board, enough to cut thru the fiber mesh that is on the surface. You do not need to actually cut the cement. Then turn the board over and push with even pressure on the back side of the score mark. The cement board will break along the score line. Make sure any cuts in the backer board are done before laying the backer board on the adhesive or mortar. If you do need to lift the backer board off the mortar to cut it again be sure to get any cuttings out of the mortar stuck to the cement backer board so the cement backer board lays flat.

step 3 Apply Mortar Or Adhesive To The Floor

Apply the mortar or adhesive bedding to the sub floor. If you are installing mortar make sure to use a notched trowel to spread it with. Also make sure there are no stray nails or other things that will hold the cement backer board off the sub floor.

step 4 How To Lay Down Concrete Board

  1. Install the backer board with ends and edges closely abutted, but not forced them together, about 1/8" or less apart.
  2. Stagger the end joints like stacking bricks after the first course.

step 5 Fastening The Concrete Board

Screw the Durock to the floor using either screws or nails spaced at 8 inches on center in both directions. Start nailing in the center of the panel and work your way outward. On the edges you must put a fastener between 3/8" and 5/8" from the edge. Drive the fasteners so that the bottom of the heads are flush with the surface and the panel and be sure to not over drive them. Make sure the panel is in good contact with the mortar or adhesive on the sub floor.

step 6 Sealing The Joints

Before you install tile you must seal the joints using tile-setting thinset and fibermesh joint tape. These are the steps to installing cement backer board joint tape. These products are sold where you purchase the Durock or Hardiboard

Get the area where the joint tape and mortar will touch damp. Use a sponge and bucket of water.

wet the cement backer board

Stretch the joint tape over the joint. Center it on the joint.

install tape on cement backer board

Press the fiber mesh joint tape to the floor, it should stick just slightly.

Press fiber mesh tape into cement backer board

Use thinset mixed to the consistency of warm peanut butter and a flat trowel. Hold one end of the joint tape and pull the trowel away from the hand holding the tape in place while spreading the thinset mortar.

Install thinset on cement backer board

For wide joints you will need to make sure that the joint under the tape is filled, it helps to pull the trowell the perpendicular to the joint to get the thinset into the joint.

Install thinset on cement backer board

After the joint tape is fully covered go over the length of the joint tape in one smooth motion to get a finish that is flat so you do not have trouble, bumps, setting tile when the joint is dry.

smooth out thinset on cement backer board

A finished cement backer board joint will show some of the top of the tape and screw head, depending on the levelness of the backer board and how deep the screw heads are set into the hardi board or durarock cement board..

finished tape joint on cement backer board

Put a thin coat of mortar over the joint making sure to fill the joint, apply the tape and then put a coat of mortar over the tape. Keep the joint as flat as possible to avoid trouble when it is time to set the tile.

step 7 Set The Tile

You are now ready to install the floor tile of your choice. See the article How To Lay And Install Ceramic Tile Floors to learn how to install ceramic tile.

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