Install Backer Board Before Laying Tile

My wife and I were remodeling our kitchen and decided to tear the old vinyl floor out and replace it with ceramic tile. Before laying tile, we had to install backer board over the subfloor. Read on to find out how we installed some Hardiebacker board in preparation for our tiling project.

The following instructions are how we executed this procedure. How-To Matthew always recommends following the manufacturer's instructions when possible.

Why Install the Backer Board?
When installing ceramic tile any type of floor except concrete, it is recommended that you first install some sort of backer board, whether that back board be cement, Hardiebacker, or Durock, you need an additional layer to keep the floor rigid enough to support the tile. The backer board will also protect the underlying floor joists from moisture.

We decided on using Hardiebacker board purchased from our local Lowes. It comes in 3'x5' sheets with a fastening grid stamped on one side. Ee purchased enough to cover 300 sq. ft. (about 8% more than we needed).

1. Mix Some Thin Set Mortar to peanut butter consistency. Use latex or acrylic thinset mortar.
2. Using a Trowel With 1/4" Notches, spread the thinset mortar on the subfloor. The "valleys" of mortar created by the notches should have just a thin coat of mortar covering the subfloor. Using the notched trowel will ensure a flat and even application of mortar.
3. Position the Hardiebacker Board on the Bed of Mortar. Make sure there is an even bed of mortar underneath the board. Leave a 1/8" gap between boards (you can use tile spacers for this).4. Screw the Board Down while the mortar is still wet. With the Hardiebacker board's stamped screw pattern, knowing where to fasten the board was quick and easy. If your board does not have a pre-stamped fastening guide, put screws or nails evenly spaced about 6"-8" apart. One full sheet of 3'x5' board takes 54 screws.
A Note on Screws: HD self-drilling corrosion-resistant ribbed waferhead screws are recommended due to their self counter-sinking head that ensures a flush install. I found regular 2" coarse thread drywall screws, which can be purchased much cheaper in bulk, worked just fine as long as you made sure the head of the screw was flush with the backerboard. In high moisture applications (i.e. showers) I would use the recommended fasteners for their added corrosion resistance.

Make sure the seams of the boards do not line up with each other, in other words, do not make a simple grid where four corners meet. Offset the pattern to where only two corners ever meet.

6. Fill Any Low Spots in the floor or if the floor is slightly out of level, you can use a bit extra mortar to even the surface out. You want as flat of a surface as possible, especially if you are laying large tile!
7. Tape and Mortar the Seams with 2" wide high-strength alkali-resistant glass fiber tape.

  1. Apply a bed of mortar.
  2. Position the backer board over the mortar and screw or nail in place.
  3. After the entire floor is covered, tape and mortar the joints.
Additional Tips
To cut the backer board, use a carbide tipped knife to score the board. With the board well scored, snap it along the score.

Traditional cement board can contain asbestos and even the newer types of backer board that do not contain asbestos are still dangerous if you inhale dust particles. This is why you should cut the boards outside if possible and avoid using any cutting method that creates dust, like sawing.

If you have to cut a lot of board, you can use a carbide blade in a circular saw but be sure to wear proper eye, ear, and respiratory protection!

If you have never tiled before, working with the backer board and mortar is good practice for the upcoming job!

Here is our kitchen and breakfast nook before and after the Hardiebacker board was installed. At this point they were ready for the tile!

Relevant Sites
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Kathy August 5, 2010 at 12:33 AM  

Matthew, this is just exactly what we need! We're about to lay down some of the floor tile. Tampa, where our house is located, has the perfect weather to do renovation jobs.

We also wanna make sure that the tiling job will be perfectly done, so we called in the pros on tile flooring. (Tampa residents should know that there are a lot of good tiling experts around!) When we meet up next week, we'll ask them about backer board. Thanks!

Aron November 11, 2010 at 1:29 AM  

Proper floor leveling should be done for the tile to be straight and not inclined for safety. That is why backer board is essential for supporting the weight of the tile, the traffic, and protection against moisture. When I had my first floor tile (Indianapolis-based contractors) installed, many precautionary measures are done for our benefit.

Anonymous,  April 19, 2011 at 2:28 AM  

Nice write up, but if you could describe how you managed to keep all the seams totally flat after taping and mortaring them that would help others. I finished my floor and every seam is raised even though I scraped it to death. It seems insane to put tape and mortar on a perfectly flat surface days before putting down the tile. It'll never stay flat. Did you sand the seams? In hindsight I think leaving the seams open until I laid the tile would've been better but I'm learning as I go. I did a cracked tile mosaic so cracking won't be an issue but big tiles would definitely not lie flat on this floor and I would be forced to rent a floor sander. As it is I just have a few small but noticeable humps. Heads up on this issue.

Alana Geikie November 5, 2012 at 12:07 PM  

Installing a backer board is definitely important for tile underlayment. Most homeowners use a backer board because the tiles easily and firmly attach or stick to it. It’s stronger than any other surface, and that includes plywood and plasterboard. Plus, it is a waterproof material, which is why it is very good to use in bathroom and kitchen tiling.

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