How to Install Durock or Hardi Backer Concrete Backer Board

Durock Concrete Backer board with a scoring knife

When tiling the kitchen, bathroom or hallway floors you can get a better finish and longer lasting seal by using an under layment first. The under layment serves to create a level surface and gritty surface for mortar to adhere to. The two main types of this product are concrete boards such as Durock and the fibrous hardi-backer boards. By following these steps you will be able to prepare any floor or surface area for tile.

Things You'll Need

• Durock or Hardi-backer board (enough square ft to cover your project)
• Thin set mortar
• Square drive screws
• Concrete board scoring knife
• Masons trowel
• 5 gallon bucket
• Water source
• Electric drill
• Square drive bit

Instructions

1. Prepare the floor. Be sure all dust and debris are removed from the floor. Check for any major dips, rises or valleys in the floor and smooth them out with thin set mortar. Remove everything from the room except for the tools you will need for the project.

2. Start in the corner of the room furthest from the door. Try to use a full sheet of concrete board if possible (if you have to cut the first piece refer to the next step). Lay the concrete board so that it is perpendicular to the floor joists or wall studs. Mark a pencil line perimeter around the board a few inches larger than the board itself. Remove the board and cover the floor area inside the pencil lines with thin set. Use your mason trowel to apply the mortar and be sure to use the edge to make ridge lines through the grout for a better grip. Use square drive screws on the corners of the board first to hold it in place and then place more every six inches or so.

3. Continue laying concrete board in the same pattern until you come across your first straight edge cut or have to cut around a water line or other obstruction. For a straight cut, measure the length of piece that you need and make a pencil mark. Hold a straight edge or 4-foot level to the pencil mark and use the concrete board scoring knife or a sharp utility knife to make a score line along the straight edge. You may have to run through it a couple of times to get a good deep score line. Lift the board and break it as you would with drywall.

4. For a cut around a pipe or other obstruction, measure the distance to the pipe from the side and end of the board and make a mark. Using a hammer and chisel or a knife, cut out a circle larger than the pipe out of the board. (remember that you will be tiling over it so the backer board does not have to be cut perfectly.) If there are pipe fittings already on the pipe, you can cut a thin strip out of the board from the wall out to the end of the pipe and fill in the gap with thin set mortar.

5. When you have installed every piece of Durock or hardi backer, go back over the floor and inspect your screws to be sure that none of the heads are sticking above the floor surface. Also remove any excess thin set that may have squeezed up through the seams and fill any gaps or holes with more thin set. When you are all done you should only have to wait a few hours before you can lay tile.