My last post discussed how to choose the right bathroom building materials in order to avoid a moldy situation down the road. Cement board is a huge part of a smart bathroom renovation because it doesn’t contain any organic matter for mold to use as food.
Today, I’m going to share how we installed cement board in a bathtub recess and what materials are needed to do the project correctly. After reading this post you’ll understand what “good” should look like so that either you can do it yourself or tell a contractor how you want the job done.
Determine Where You Want the Cement Board Installed
The first step in any cement board project is to determine where you want it. In our case, Rob (my brother-in-law whose bathroom we’re working on) wanted the cement panels in the shower surround but preferred to have fiberglass faced purple board serve as the top border.
It helps to also know the dimensions of a typical cement board panel. They can be bought as either 3 ft by 5 ft or 32 inches by 5 ft. The manufacturers do this because bathtub surrounds have a back wall that is 5 ft long and both adjacent side walls are anywhere from 32 to 36 inches wide. This makes installing cement panels much easier because it involves less cutting.
Ideally you want the cement board to cover any area that will be exposed to water. I don’t know about you but the front wall that contains the showerhead in our bathtub gets saturated with water. This is a good reason to choose the 36 inch wide cement panel because it will extend out more and add protection against mold forming on any existing drywall that is paper faced.
If you can do it, think about making the ceiling out of cement board in the bathtub recess, too. Remember, hot air rises and in the bathroom it is especially full of moisture. Even if you do have a fan the ceiling still gets a blast of warm air every time a shower is taken (and even more so if you have teenagers who like taking long showers).
Choose the Correct Screws and Joint Tape
When you buy cement board it requires the same installation materials as drywall but with a twist. You’ll need to buy cement board screws that have a special corrosion resistant coating and are much stronger than drywall screws.
In my last post I discussed how fiberglass drywall joint tape should be used to make wallboard panels one cohesive unit. The same principle applies to cement board. The tape you need to use is alkali-resistant, fiberglass-mesh, and polymer coated. The polymer coating on the tape protects it from the chemicals in the mortar within the cement board itself. This tape can also be used where cement board and drywall meet each other.
Instead of using drywall joint compound to embed the tape in the cement board you should use thin-set mortar. We utilized the same thin-set that will be used to attach the tiles.
Having the cement board, alkali-resistant screws & joint tape, and mortar will get you one step closer to installing the tub surround the right way.
Let the Installation Begin (With the Back Wall)
In our project, we decided to install the upper back wall panel first. Since the width of the back wall was a little more than 5 feet wide we were able to simply install a full panel without having to trim it. I spaced the screws on the studs about 8-10 inches apart from each other. Attach screws at most 1/2 to 1 inch from the edge of the cement board. Otherwise, the cement will crack.
I prefer to add screws to the top of the cement board then use a level to trace a vertical line indicating the stud position behind the cement panel. Unless you’re Superman or Superwoman it’s hard to see through cement and this step makes me feel better about the screws being directly centered on the studs
To make the process easier I highly recommend using an impact drill/driver like this Ridgid I’m holding. This is hands down my favorite tool and if you’re doing any DIY projects you need to buy one of these
The Americast bathtub we installed had a good 1 inch lip on it, which we attached to the studs using galvanized roofing nails. We also shimmed out the walls with 1/4 inch lath strips so the cement board would sit flush with the lip or slightly beyond it. This will allow the tiles to rest beyond the lip of the tub when we secure them to the cement board later in the project.
I measured the distance from the top of the nail (holding the lip to the stud) to the bottom of the upper cement board panel and subtracted an 1/8 of an inch. This gave me the size of the bottom cement board. It’s important to get this measurement correct because it’s tough to cut 1/2 inch from cement board!!
Once we obtained the height of the bottom cement board panel I cut it using a special carbide tip knife and the straight edge of my level. Since the cement board is sandwiched between fiberglass mesh tape it needs scored until the mesh is fully cut. I scored one side of the cement panel until the mesh completely severed.
Then I bend back the scored portion of the cement panel to expose the other side of the mesh tape. You can either cut the tape with the carbide tip knife or cut it with scissors.
The lower cement board panel was installed just like the upper portion, and rested just above the lip of the tub. One big tip is to make sure the tapered edges of both the lower and upper panels abut each other. This is super important because it provides a recessed space for the joint tape to sit in. Otherwise, you’ll have a hump at the joint and this will cause your tile installation to be uneven & look bad.
Our back wall was pretty simple to install. The two side walls are straight forward as well, but I’m going to explain how we attached them to the studs in my next post. There are some details I feel are really important to share and that’s why there will be a Part 2 to this tutorial
So I hope this was helpful and if you have any questions please ask away in the comment section below. To get more immediate updates and some funny pictures join me on Facebook and Like Home Repair Tutor by clicking this link.
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Make it a great day!