How to install Hardie^® Backer cement board on floors

If you’re looking to install new tile flooring, choosing the right materials will be essential to your satisfaction with the finished project. It’s important to select a tile backer board that will defend your home against the threat of moisture damage, so you can rest easy knowing you’ve done everything you can to ensure your project lasts.

When installing Hardie® Backer cement board on wooden floors, we recommend using our quarter-inch cement board.

What You'll Need:

• Modified dry-set cement mortar and/or dry-set cement (for use between subfloor and cement board only)
• 2” wide, high-strength, alkali-resistant glass fiber tape
• Corrosion-resistant roofing nails or 1.25” minimum Backer-On screws
• Trowels
- For Hardie® Backer cement board to subfloor, use a quarter-inch, square notch trowel
- For tile to Hardie® Backer cement board, use the specified size of trowel for your tile
• Carbide-tipped scoring knife (recommended), utility knife, or shears

Before you get started, you should determine if your floor is suited to Hardie® Backer cement board.

You should have a minimum of ⅝” thick exterior grade plywood or 23/32” thick OSB with minimum exposure 1 classification. If your floor joist spacing is more than 16” on center, you should consult the building code for the appropriate subfloor thickness requirements. Do not install Hardie® Backer cement board on joists more than 24” on center.

If your floor meets the requirements, the next step is to ensure that it is structurally sound and free of damage. Replace any warped, missing, or uneven sections of flooring so that you have a flat and clean surface. Once you’ve done that, you’re ready to cut your Hardie® Backer cement board to size. Check out our video on how to cut Hardie® Backer cement board for detailed instructions.

When determining how to arrange your Hardie® Backer cement board, remember the following rules:
• Keep a ⅛” gap between board edges
• Keep sheet edges ⅛” back from walls and cabinet bases
• Stagger cement board joints in a brick-laying pattern
• Don’t align boards with subfloor joints
• Never align four corners of boards to meet at one point

Now you’re ready to attach your board to your subfloor.

How to Install Hardie® Backer cement board

1. Apply a supporting bed of mortar or modified thinset to your subfloor with your trowel.
2. Using a sliding motion, firmly and evenly embed your Hardie® Backer cement board in the wet mortar.
3. Using the screw pattern as a guide, fasten your Hardie® Backer cement board with nails or screws every 8” on center over the entire surface.
4. Keep screws between ⅜” and ¾” from board edges and 2” from board corners.
5. Set your screwheads flush with the surface. Be careful not to overdrive them.
6. Fill all the joints with the same mortar used to set the tiles.
7. Embed 2” wide, high-strength, alkali-resistant glass fiber tape in the mortar and level.

Installing Hardie® Backer cement board to a wooden subfloor is as simple as that! Hardie® Backer cement board can be used with nearly any kind of tile, whether ceramic, porcelain, or natural stone.

Here’s how to add your tile over your Hardie® Backer cement board:

1. Wipe the surface of your Hardie® Backer cement board clean with a damp sponge.
2. Spread the modified thinset with a notched trowel appropriate for the size of tile you are installing.
3. For best results, comb the ridges in one direction only.
4. Twist or press and beat in tiles.
5. Allow a minimum of 24 hours curing set time before grouting.