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How to Install Bathroom Floor Tile: Part 3

Cracked floor tiles are unsightly nuisances that unfortunately make bathrooms look crazy bad.

Our last post shared why we sometimes use HardieBacker on top of bathroom wood subfloors. Today you’ll see the ins and outs of how to dry-fit HardieBacker on top of your bathroom floor.

Once HardieBacker is in place you’ll have a crack-resistant foundation to lay any type of porcelain or ceramic tile.


Measure Your Bathroom Floor Dimensions

You’ll need to measure the length and width of your bathroom floor. These dimensions will give you a rough idea of how to lay out your HardieBacker (or let you know if you can play a quick game of Twister, just kidding).

Measure the length and width of your bathroom floor to determine how to layout HardieBacker

Keep in mind that the HardieBacker joints shouldn’t rest directly on top of the wood subfloor joints.  Also, if you have to use several HardieBacker panels their 4 corners should never meet at one point as this will create a weak spot for tile to crack.

We discussed other important ideas to consider when prepping for HardieBacker in my last post.

Our dimensions for this bathroom were 61 inches by 60 inches. This was awesome because the HardieBacker panels we were using were 60 inches by 36 inches and therefore we’d only have to make one cut.

After looking at the wood subfloor layout we were able lay a full HardieBacker panel flush with the back wall where the vanity would reside. Sorry for the super bright light in the photo below, we didn’t have the vanity light installed yet. Notice there is a 1 inch gap between the left wall and left edge of the HardieBacker panel. We decided to fill this in with thin-set since there wouldn’t be foot traffic on that section of the floor.

We laid a full HardieBacker panel against the back wall where the vanity would reside
Make sure the HardieBacker joints are not directly on top of the wood subfloor joints

You’ll also need to consider how far to place the cement board into the doorway.

Our goal was to have the transition between the hallway flooring (hardwood once it got installed) and the tile in the bathroom directly centered underneath the closed bathroom door.

Place HardieBacker directly centered underneath the closed bathroom door

To make your new bathroom floor tile look good I highly recommend undercutting the door jamb trim. This allows the HardieBacker and new tile to slip underneath the trim instead of butting against it (which doesn’t look good at all).

We placed a new porcelain tile on top of the dry fit HardieBacker and slid it up to the door trim. Then Rob used his Bosch multi-tool to undercut through the door trim.

Undercut your door trim to allow the tile and HardieBacker to slide underneath it

Voila, a perfectly cut space for the new tile to slide under. You may have to coax the cut trim piece out with a hammer and screwdriver or chisel but it won’t take much effort. After all is said and done there should be roughly a 1 inch gap between the door trim and the bathroom wood subfloor if you’re using 1/4 inch HardieBacker.

There should be roughly a 1 inch gap between the door trim and wood subfloor

How to Cut HardieBacker Cement Board

Once you know the general layout of your HardieBacker  you can cut it to size. In this project we cut the waste pipe for the toilet because we wanted to have the toilet flange sit on top of the tile. Otherwise, the toilet won’t make a good seal with the wax ring and this could lead to a water leak that might ruin the floor & wood support structure (note, this leak will likely happen on a holiday or the middle of the night-i.e. anytime a plumber isn’t working).

We placed the HardieBacker panel on top of the hole in the floor where the waste pipe use to be. We also ensured the panel was 1/8 inch away from the wall and the bathtub. Then we drew the outline of the hole on the underside of the panel from the basement.

Transfer the dimensions of the toilet flange to the HardieBacker

We were lucky to be able to do this but if your bathroom is on a second floor you’ll just have to measure the location of the hole and transfer these dimensions onto the HardieBacker.

To make a perfect hole in the HardieBacker we made a scribe from a sturdy piece of plywood then drilled two of the screws we were going to use to install the panel into the plywood. The screws will need to be drilled into the plywood so that the distance between them is the radius of the hole.

Make a scribe that will cut a perfect hole in HardieBacker

Drill the scribe into the HardieBacker panel so that one screw is in the center of the hole and the second screw sits on the edge of the hole. The screw that sits in the center can be drilled most of the way through the HardieBacker. The screw that is on the edge of the hole should just touch the HardieBacker enough to score it.

Drill the scribe into the HardieBacker panel

With the scribe in place turn it clockwise (or counterclockwise if you’d like) and score the outline of your hole. Then, (and this isn’t a super ninja skill but I’d like to think so) turn the HardieBacker over and insert your scribe’s center screw into the small screw hole. Scribe the bottom of the panel like you did on it’s top surface.

Scribe the other side of the HardieBacker

Take a hammer and hit the center of the scribed hole. BAMMM!! You’ve got a perfect circle in your HardieBacker. High fives anyone???

Use a hammer to hit the center of the scribed HardieBacker hole
The scribe technique makes perfect holes in HardieBacker panels

We placed the HardieBacker panel on the floor and positioned it over the waste line. Then dry fit a piece of ABS pipe through the hole in the panel to make sure all was good.

We only needed one more piece of HardieBacker to completely cover the bathroom floor.

To cut straight lines you should use a straight edge (like a level or drywall t-square) and a carbide tipped cement board knife. You’ll have to make a few passes with the carbide knife and then you should be able to simply snap the HardieBacker with your hands.

Use a stright ede and carbide knife to cut HardieBacker

Don’t Make this Mistake

At the beginning of this post we wanted the HardieBacker to be in the door jam such that the transition between the tile and hallway would fall underneath the closed door.

Well apparently I must have missed my coffee break because I forgot to account for this.

So we had to cut a 1/2 inch strip of HardieBacker and place it in the door jam.

Don't forget to have your HardieBacker extend into the door jam

The dry layout of the HardieBacker is the first step in the installation process. The next move forward deals with using thin-set and screwing the panels to the wood subfloor.

My next post will walk your through this and I’ll share a big tip I got from the HardieBacker technical support line.

The summary points of this post are as follows:

  • measure your bathroom floor dimensions
  • position the HardieBacker panels so their joints don’t overlap the wood subfloor joints
  • cut the door jam trim to allow the new tile & HardieBacker to slide underneath it
  • use a scribe to cut perfect holes in HardieBacker
  • use a straight edge and carbide cutting knife to trim HardieBacker
  • don’t forget (like me) to place HardieBacker in your door jam opening


What’s Next

Hopefully these tips helped.

HardieBacker isn’t the only option for bathroom floors. Schluter DITRA is also a great method and one we use a lot.

If you’re doing a bathroom remodel and need help, join one of our online courses – they’ll make your bathroom renovation much easier!

Let me know if you have any questions and I’ll do my best to help.



HardieBacker Installation