Tips for a Better Cement Backer Board Layout

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You already know you have to install cement board before laying floor tile or wall tile. How do you plan the cement backer board layout? Where do you start?

There are a few hard-and-fast rules you should know:

#1 If you are tiling over a concrete floor you are already done!

Easiest. DIY. Project. Ever.

You don’t need backer board. Just make sure the surface is flat enough, evening it out with self-leveling concrete, if needed.

The point of backer board so to cover a plywood subfloor, not a concrete slab.

#2 A cement backer board layout should be staggered.

It’s kind of like building a wall of Lego’s.

If you set each one directly on top of each other it is unstable.

You create a stronger, more stable floor by staggering the backer board.

Not this:

Likewise, four corners of cement board should never meet at one point. Now imagine actually doing that and placing something heavy right at the meeting point.

While this is extreme, it’s basically what happens on a much larger angle.

Chances are a tile will overlap to some extent but if it’s close due to your tile layout, you’re more likely to have a crack form sometime in the future. Again, it’s not a guarantee but we are increasing the odds that our floors will stay intact as long as possible by staggering the cement board.

#3 Do not align cement board with subfloor joints.

This goes along with the same logical argument is staggering.

Revisit the lego photo above–matching the cement board with subfloor joints is just asking for trouble.

Given these rules, where should you place the full pieces when you start planning a cement backer board layout?

A room isn’t always square and simple as my spectacular Lego layout. In addition, we need to account for any thresholds on the edges of the room, if you are also planning on tiling them.

Behold a threshold!

On one hand, you might consider placing the large pieces of backer board where you expect the most weight. Appliances and cabinets are the obvious winners in the weight competition. However, after experiencing kids run like elephants through a house I want full pieces of backer board on the high traffic areas. These high traffic areas are going to experience more movement then a sedentary range or refrigerator.

This is why I would like to start my layouts along the walls where there are interior entryways to a room. Exterior entrances are a nice to have, but interior entrances to a room are used many more times than going in and out of a house.

Notice the operative word in the first sentence of the last paragraph is “like” not “always.” A number of other factors may come into play. For instance, what is the size of the room in relation to the size of the backer board? Does laying the backer board a certain direction create less waste? Can you prevent more cuts by running the boards one way versus another?

A floor example…

Let’s try planning a cement backer board layout for the kitchen in my pier and beam house as an example. The kitchen is 13′ x 15′. Since backer board generally comes in 3′ x 5′ sheets we could go either direction since the 15′ wall is cleanly divisible by 3′ AND 5′. In either case, we have to account for some of the thresholds because I plan on installing granite thresholds.

Let’s look at two potential layouts:

Layout #1: Vertical

Layout #2: Horizontal

Layout #2 is actually the better layout. Each of the first four rows of cement backer board is exactly three sheets. You have leftovers from the last two boards required in the last row, but not the leftover scraps of four separate boards as there are in Layout #1 (I’m not counting the scrap from the fifth one because there is no way we wouldn’t just reuse two of the other scraps in that spot).

Just so we are clear, here are your options with the last fifth piece in question:

The figure to the left is a full 3′ x 5′ sheet and two scraps. The figure on the right addresses any of you who thought, “Hey, what about putting all that leftover to use!” Unfortunately, the remaining four pieces do not fill in that last section even though it is in an ideal space to place pieces (along a wall and below a cabinet). No matter what layout you choose you are looking at a full extra sheet.

Ahhhh…regret! Why did I not do this calculation?

Looking back I should have as it would have saved lots of time with less cuts and more efficient use of boards. Instead, I addressed both problematic areas (elephants running through and permanently installed heavy objects) by using full sheets on the entrances of the room and along the cabinet walls. I was left with a mishmash of smaller pieces in the center of the kitchen (READ: a hell of a lot more cuts and time).

It started off good…

It also doesn’t look so bad along the upper wall here:

Don’t do this. Plan it out ahead of time (not at the eleventh hour–or in reality 2 am at the end of a long DIY house remodel weekend which is pretty much when the picture at the beginning of this post was taken) and make your life simpler.

A bathtub surround example…

When it comes to tub surrounds the layout is pretty simple. One thought is to put larger sheets towards the bottom since lower areas are exposed to more water that upper areas. You can always put in smaller pieces above where there is a heck of a lot less splash back.

The gaps between boards do not matter in the instance where you waterproofing with Schluter Kerdi or some other similar product between the cement board and the tile. The point is that it is easier to install larger pieces lower than it is to deal with one higher up the wall.

Gaps matter a little more if you are adding in 10 mil plastic as your waterproofing between the framing and the cement board. In this case you are relying on the plastic to catch the water that seeps through.

When it comes to a typical 3′ x 5′ bathtub surround consider placing a piece of cement board vertical under the shower head and opposite wall. On the back wall you can stack two full sheets on top of each other and put a smaller piece above those two.

A shower example…

A shower is similar to a bathtub surround in that prioritizing full sheets of cement backer board at the bottom is most important. The bottom area of a shower surrounding the shower head bears the brunt of water. The cement board layout itself depends on the dimensions as a walk in shower is more likely to have windows and other funky lengths.

In my own shower the backer board started off like this:

Unlike a floor install, you certainly will not be stomping on the walls. You’ll be more concerned putting blocking in the right spot so you can securely attach the boards to the framing. That or cutting down the cement board to match the current framing.

We have used HardieBacker cement board for our floors, walls and countertops with no complaints. Check out their installation instructions here as a starting point if you would like more information.