I finished installing the bathroom walls, the shower pan, and surprisingly passed the waterproofing test, so now it’s time to get the floor ready for tile. Before I just slap some tile on, like everything else, I have to prep the floor first and this is done by installing cement backer board.
Why backer board?
In my vast research, I saw so many people asking if the cement board was necessary, couldn’t they just install tile directly on the plywood subfloor? The answer is ABSOLUTELY not and here is why.
First and foremost, tile, mortar, and grout are not waterproof. Water will get through to the subfloor which could cause water damage along with mold and mildew problems.
Second, plywood is aptly named, as it is pliable. Though it may seam sturdy, it moves and flexes a lot more than cement board, which could cause your tiles to break and it buckle.
Because I do not want to be tiling this floor again in a year, I will be installing cement backer board. For the shower walls I chose Durock cement board because it came in a depth option that met my needs, however, I am changing it up for the floor. I will be using Thomas hardie cement backer board with a 1/4 inch depth. I didn’t want to add too much depth as we already have 2 layers of subfloor.
Planning and cutting the backer board
Cement backer board comes in a 3 x 5 ft sheet, so first I had to plan the most efficient way of laying the board on the floor. I used this app, which allows you to enter specific dimensions of your tile and move it around on the screen until you find the right spot.
Here, I entered the dimensions of the room and indicated the tile was 3 x 5 ft.
Using this tool allowed me too see if any of the sheets would be too small on either end and adjust accordingly. Luckily, it wasn’t too trick and I could start by laying a full board in the corner.
Cutting the board
Unfortunately, Hardie board is not as easy to cut as Durock cement backer board. Cutting these bad boys requires a skill saw and a special blade.
It also makes a huge mess, so having an area to cut outside is a must!
I laid the full boards until I came to areas where I needed to cut. Larger cuts were easy, but required measuring and precision.
I also had to contend with other obstacles like door frames. Here you can see the board would not fit under said frame.
I used my oscillating multi-tool to cut the door frame to allow the cement backer board to slide underneath.
Here you can see the cement board fits perfectly.
I had to make sure that the frame was cut enough so that it would fit with a layer of mortar underneath too, but it is kind of hard to see in this picture.
Cutting the hole around the toilet flange was a little tricky as well.
For this, I measured to the center of the hole from each side and marked it. Then, using the diameter of the flange, I marked the circle I needed to cut on the board.
The skill saw is a beast, which makes cutting a circle very difficult. Propping the board on sawhorses on each end, I pressed the saw down multiple times making more of an octagon rather than a circle.
But it worked, so no complaints here. Thinking forward, I know that my toilet flange has bolts (that connect the toilet to the flange) screw directly into it, but if you have a more modern flange, you would want to leave room on the sides for the bolts to slide in and out.
After making all the tricky cuts, I had my boards all laid out and ready for the next step.
Thin-set mortar… again.
Though it may seem like over-kill, you have to apply thin-set mortar to the subfloor before screwing it in. This is mainly so that there are no gaps or voids between the two boards that would lead to buckling or cracking tile later down the line.
As I mentioned in my previous post, not all thin-set is created eq
As I mentioned in my previous post, not all thin-set is created equal. For this application, I used a latex modified thin-set to ensure maximum bond strength.
First, I applied it with the flat side of the trowel.
Using the notched side of a 1/4 in. trowel, I combed the mortar to ensure it was applied evenly.
Then I placed the board on top of the mortar and pressed firmly to set and attached with cement board screws.
I repeated this process with the boards in small areas because you still have to tape the seams and you want to avoid walking on the boards until the mortar has set.
Just a side note, this was taking a hell of a lot longer than I hoped it would. They make it look so quick in the YouTube videos…
Next, I pressed fiberglass cement board tape over the seam and applied thin-set over the tape. You have to try and make the transition as smooth as possible, or it will be hard to level your tile.
This is the first chunk I finished. Now only almost all of the rest of the bathroom left…
So I just kept going…
and going…
and going… Finally, I allowed the mortar to set for a full 48 hrs.
But I’m not done yet, as much as I want to be. Because this floor may be exposed to a good deal of moisture (you should see my kids take a bath), I need to waterproof the floor like I did with the shower walls.
Waterproofing the floor
I used Redgard, the same waterproofing membrane I used for the shower walls.
I started by moistening the floor with a wet sponge and using a paintbrush around the perimeter and the hard to reach areas.
Then I slopped it all over the floor.
And used a paint roller to spread it evenly.
Now I have a really red bathroom. My kids are going to be very sad when they learn this is not the final product.
Wall to floor seam
To finish it off, I had to waterproof the wall to floor seam. I used a silicone sealant for this.
Applying a good amount with the caulk gun, I made sure that there were no holes or cracks.
Finishing the shower curb
The last and final step was completing the outside of the shower curb. I didn’t take any great pictures, but I repeated the process I used for the interior of the shower pan on the outside using the Kerdi band and mortar. You can check out that post if you want the details.
I didn’t realize how time-consuming this part of the project would actually be. Between taking the boards in and out for cutting and measuring, getting the cuts just right, mixing and applying the mortar, and screwing the boards into the subfloor, this took me about 3 days to finish. I have to throw myself a bone though, as I was also homeschooling my children.
Now I am finally ready to start the fun stuff! Up next, tiling the floor!
I started this blog in the hope of inspiring other people to try something new, especially if it is unexpected. If you like what you are seeing, please like, comment, or share! Thanks for reading!