Learning how to install cement board on a floor properly is the best thing you can do for a solid, mold-resistant, crack-free tile floor that will last.
Budget at least a full day for this job. Especially if it is your first time installing cement board, more extensive floors may need multiple days.
Tools & Materials Needed
First, let’s start with the cement board itself. If you take a trip to your local hardware store, you’ll likely come across three leading brands. Each board will have slightly different characteristics. One might have more flexibility; another may cut easier.
But rest assured, as long as you choose a cement board in this category listed for flooring, you can’t go wrong.
Durock Cement Board
Durock by USG Brand is a known favorite of flooring contractors because it is slightly lighter in weight and cuts quickly (EdgeGuard patented edge performance PDF). Comes with a limited 30-year warranty.
Hardiebacker Cement Board
Known to be more fibrous than other cement backerboards. Along with stiffer than Durock. Often said the preferred brand by tile contractors. It comes in two options (PDF):
HardieBacker 500 Cement Board: Features a smooth finish and moisture resistance
Hardiebacker 1/4″ Cement Board: Lightweight and easy to cut with no mesh needed. It can even be used on countertops.
Wonderboard Cement Board
This brand doesn’t soak up thin-set as much as Hardiebacker does, giving you more time to adjust tiles if needed.
Permabase Cement Board
The main feature of Permabase is the EdgeTech that allows fasteners to be installed closer to the edges. It’s also GreenGuard certified for better air quality.
Other Materials Needed
- Alkali-resistant fiberglass mesh tape made specifically for concrete board
- Thin-set – Make sure to get latex-modified mortar
- Cement board screws – Size will depend on the thickness of the cement board and underlayment.
- 1/4″ notched trowel for spreading the thin-set
- Straight edge and knife for cutting the cement board
- Tape measure
5 Steps To Installing the Cement Board To the Floor
1.) Fix Any Issues With Subfloor
If you want the most durable and long-lasting tile floor possible, make sure your subfloor is solid. Before installing 1/4″ or 1/2″ cement board, make sure the floor doesn’t make any sounds. If it does, simply screwing down the plywood to the floor joists will solve this. But, once the tile goes on, it becomes challenging, if not impossible, to fix.
If you have not figured out what kind of subfloor you have. Simply remove a heating register and look at the edges of the wood. Some common subfloors you might see are:
- Vinyl flooring glued over 1/4″ wood underlayment. If you have this for a subfloor, you will want to keep floor height in mind. The typical 1/2″ cement board may raise your floors too much. Use 1/4″ cement board. If the subfloor underneath the tile is 3/4″, you can use 1-1/4″ cement board screws to fasten it down.
- 1/2″ Plywood with 5/8″ particleboard underlayment. Take the particleboard off and attach the plywood to floor joists using 1-5/8″ screws every 6″. Then, install 5/8-in. CDX plywood, by screwing it into the subfloor with 1-5/8″ screws. Space the screws every 4″.
- 3/4″ Tongue-and-groove plywood, or OSB (oriented Strand Board). No additional layers of plywood are needed. Screw the floor down using 1-5/8″ screws spaced at 6 inches apart.
2.) Sink Fasteners and Remove High Spots
Examine all the plywood seams using a straightedge by holding it perpendicularly to the seams. If there appears to be “teetering-tottering” over any joints, use a belt sander to sand down the ridge to make it level with the floor. Also, if there are any “proud” nails or screwheads, you will want to sink them in flush.
3.) Lay Down Thin-Set Mortar and Cement Board
Thin-set is what will give your cement board an even, and void-free surface to lay on. Most people think it’s for bonding (which it does), but really the screws are what holds it down the most.
Before laying down the thin-set you want to cut and install all the cement boards for the space. Once that is done you can lift them up and spread the thin-set mortar. Use a 1/4″ notched trowel for best results.
Comb out the mortar in straight and even parallel rows.
You can install the cement board and screw it down to the underlayment with the thin-set spread. Follow manufacturer’s recommendations, but most say screw it down every 4-8″ along the edges.
4.) Tape and Mortar Seams
Fill the joints with a type-1 organic adhesive or latex-fortified mortar. Immediately followed with mesh tape.
Lay the cement board fiberglass tape over every seam (it’s also sticky on one side to help keep it down).
Lastly, use a large putty knife or trowel to spread the mortar thinly over the tape. Be sure that you remove any high spots or ridges.
5.) Another Layer Of Thin-Set and Lay Tile
The last step is to add another layer of thin-set on top of the cement board to bond the tile.
Be sure to only mix up enough thin-set to last a half-hour at a time. While also making sure that each tile is seated solidly in the thin-set.
If you follow all these steps, you’ll have a beautiful, long-lasting, crack-free tile floor.
Installing cement board is not a difficult task. But, for some reason, people seem to mess it up. Here are some common mistakes and how to avoid them.
Installing Cement Board on a Concrete Subfloor
You might think you need to install cement boards on concrete because that is how you’ve seen it done. Although you could use some concrete screws and install the board on concrete, you are usually better off skipping it.
Instead of installing cement board on concrete, use a self-leveling compound. This will level the floor and provide a nice smooth surface for the thin-set and tile. Skip the cement board.
If you’re worried about the floor being cold- you will need to add some insulation. Typically this is done with a layer of rigid foam insulation and then a plywood subfloor. You would follow the steps above just like a normal subfloor.
Not Using Mesh Tape
As always, follow manufacturers’ instructions. Most will want you to install alkali-resistant fiberglass mesh tape.
The mesh tape helps strengthen joints to prevent cracking. This can be a significant issue. Take the extra time and use the tape.
Using the Wrong Fastners
Each cement board will have specs on fastener spacing and what type to use. Although, that doesn’t stop some people from trying to use drywall screws, nails, etc.
You want to use cement board screws in the correct size and spacing, so the board is held down properly. Some cement backerboard will have the recommended locations for fasteners printed on the board itself. No measuring is required.
Forgetting To Stagger the Seams
Cement board is forgiving in that it really doesn’t matter which way it goes in. You can lay one piece one way, then the adjoining pieces could go the other.
Whatever you do doesn’t matter, as long as you don’t have four joints that come together. Think of it like a brick pattern. While at the same time, think of how to use the material most effectively. Helping to keep costs down.
Also, don’t forget to not make the joints the same as your subfloor wood seams.
Not Using Thin-Set Under the Cement Board
Again, just follow the manufactures instructions. The instructions will not give you options to skip the thin-set and use glue, etc. They require it for a reason.
Thin-set goes on the bottom and top of the cement board.
Hopefully, this guide has answered all your questions on how to install cement board on floors.
Please share your project with us! Email a couple of photos and a summary of how your cement board installation went, and we will post them on our website!
HardieBacker Installation Instructions (PDF)
Durock Installation Instructions (PDF)
Wonderboard Installation Instruction (PDF)
Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.