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DIY Bathroom Remodeling: Phase 5

How to Cut Circles in Cement Board

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Make a Perfect Circle in Cement Board with a Scribe

Every time we see  a nice bathroom in a magazine article or on HGTV we’re always in awe. But we also wonder how the installers got the tile to look so beautiful.

If you’re curious like us then this post will help demystify the process.

Every tile job begins with the substrate, e.g. cement board, KERDI-BOARD, Wedi, etc.

Our previous tutorial dealt with attaching cement board to the back wall of my brother-in-law’s new bathtub recess.

Since cement board panels come in 3 ft x 5 ft sections ( or 32 inch by 5 ft sections) it makes the installation much easier than you’d think.

With that said, there are some tips that make the final steps of cement board installation less frustrating. 

Cement Board Installation on Side Wall

Cement board panels come in sizes that accommodate the bathtub recess. In our case we bought 32 inch by 5 ft panels. Then, Rob cut out the existing drywall with a Bosch oscillating multi-tool.

Both of us love this kind of tool because it helps with so many different projects. If you don’t have one yet it might be something to look into.

I rested the cement board panel on the bathtub and pre-drilled cement board screws about a quarter inch into its face where there were studs.

The screws in the photo below were about 1 inch from the top of the panel to ensure I didn’t crack the cement between the mesh.

Pre Drill Cement Board Screws to Make Installation Easier

I’ve learned to do this when hanging heavy cement panels by myself.  With no extra hands you need to be crafty to ensure you don’t get hurt and actually hang the panel the right way the first time.

We lifted the panel up to be flush with the purple board and made sure the bottom was above the roofing nails that held the tub lip to the studs.

At this point we drilled the screws the rest of the way through the cement board and into the studs. You should drill a screw every 8-10 inches up and down the stud. It’ll take the Incredible Hulk to yank the cement board off the wall.

We also used a  piece of cement board to fill in the area next to the tub. It’s better to show you what I’m talking about in picture format.

Use Cement Board to Fill in the Area Next to the Tub

This area is super prone to water damage. I’ve observed this first hand at my rental homes and learned my lesson not to use anything other than cement board for this section of the bathroom wall.

And it’s best to pay attention to this area when waterproofing it with something like RedGard or Ardex 8+9.

How to Cut Circles in Cement Board

The last thing you want when cutting a hole in your cement panel is realizing it’s in the wrong position.

But you only need patience, a measuring tape, and pencil.

In our tub we only had to worry about cutting a hole for the shower handle and the tub spout.

The Cement Panel Needs Two Holes CutThere were 6 simple actions we needed to take to eliminate the possibility of messing up these cuts.

  • Remember the Cement Panel will be just above the roofing nails holding the tub lip in place
  • Get the distance from the center of the Shower Handle stem to the back wall
  • Measure the distance from the center of the Shower Handle stem to the top of the roofing nails
  • Get the radius of the Shower Handle mounting hardware
  • Measure the distance from the center of the Tub Spout Copper Pipe to the back wall
  • Get the distance from the center of the Tub Spout Copper Pipe to the top of the roofing nails

The picture below shows the distances that we measured for the shower handle – it was 13 1/4 inches from the back wall and 36 5/8 inches from the top of the roofing nails.

This location marks the center of the shower handle on the cement panel.

Find the Center of the Shower Handle on the Cement Board

We carefully measured the radius of the shower handle mounting hardware and determined it was 2 1/2 inches. But I wanted a little wiggle room for the final cement board hole and made it 2 13/16 inches.

Measure the Radius of the Shower Handle

Cutting a perfect hole in cement board is very easy, although it does take elbow grease. We made a scribe with two cement board screws and a sturdy piece of scrap wood about 2 inches wide by 6 inches in length to accomplish this task.

The first screw will need to be drilled through the wood 1 inch from the edge. The second screw will need to be drilled through the wood at a distance equal to the radius of the shower handle mounting hardware, so in my case 2 13/16 inches.

Make a Perfect Circle in Cement Board with Wood and Two Cement Board Screws

We drilled one of the scribe screws through the mark on the cement board that indicated the center of the shower handle.

Then we drilled the second scribe screw into the cement board about 1/8 of an inch. This allowed us to turn the scribe and cut through the mesh and cement in the panel.

Make a Perfect Circle in Cement Board with a Scribe

At this point the hole is half way to completion. Turn the cement board over and insert the scribe in the center hole.

Use the scribe to cut through the mesh and cement on the back of the panel.

Use the Scribe to Score the Back of the Cement Board

Now the scored circle can be removed from the cement board using a hammer. Give yourself a pat on the back, you’ve got a perfect hole for the shower handle.

Remove the Scored Circle with a Hammer

We used the same measuring method to mark the center of the copper pipe for the tub spout.

And this time the hole was created using an old hole saw. If you don’t know what a hole saw is that’s okay.

They are used for cutting a hole into doors, specifically a 1 inch hole for the deadbolt, and can be bought at any hardware store.

Use a Hole Saw to Cut a Hole for the Tub Spout PipeThe finished product doesn’t look too shabby.

Perfect Holes for the Tub Spout Pipe and Shower Handle in Cement Board

We screwed this side wall cement panel into the studs the exact same way as all the other cement boards.

We went from having studs in the bathtub recess to cement board on all three walls in less than one day.

Having cement board as a substrate in your bathtub or shower will severely reduce the odds of developing mold.

It serves as a great substrate for ceramic, porcelain, and glass tiles. And it’s cheap ($10-12 per panel).

Rob and Janeen (my sister) want to use subway tiles for the tub surround, and having plumb (straight up & down) walls made from cement will ensure the whole job will go smoothly.

 

What’s Next

If you’re curious about how to waterproof this kind of space read our next tutorial.

We used RedGard but you could also use Ardex 8+9.

Keep in mind that cement board isn’t the only type of backer board for showers. KERDI-BOARD and Wedi are also fantastic options.

If you’re doing a custom bathroom or shower remodel check out Bathroom Repair Tutor. The detailed video tutorials are super helpful and focus on getting professional results.

Here’s the link to Bathroom Repair Tutor

Cheers,

Jeff Patterson

 

 

 

 

18 Comments
  1. Wendy says:

    Thank you for the great detailed post. In addition to the physical ones, I appreciated your emphasis on patience to do things right. I tend to get impatient with this kind of work and if I do, I usually regret it later. Great job!

    1. Jeff says:

      No problem Wendy. Thanks for your kind words. I have to remind myself to slow down at times, too 🙂

  2. Shan says:

    This is the best instruction for installing cement boards. One question: why one has to install the cement board just above the roofing nails, not over the tub lip? Thank you.

    1. Great question.

      Here’s the deal, if the cement board is installed down over the tub lip it won’t be plumb. Out of plumb cement boards will in turn lead to your tile looking off center where the two adjacent walls intersect. This is especially true if you have small tiles, e.g. 2×2 inch or even 4×4 inch.

      Let me know if this makes sense 🙂

      I understand there might be a concern that water will get behind the walls. But you will be in good shape if you caulk where the lip meets the cement board and then caulk the bottom of the installed tile.

  3. Arienne says:

    Love the technique to scribe with screws and hammer out circles/holes in the cement board. Worked very well for me this afternoon. Thanks for your wonderful explanations and sharing!

    1. Arienne, you’re super welcome. So glad it worked for you. Let me know how the rest of your project goes. I’d love to see pictures as well 🙂

      1. Arienne says:

        Okay, so it’s only 4 months later, and I’m still working on that shower interior! Mortaring rocks takes a long time. Thanks again for your know-how, Jeff.
        Arienne

        1. Hi Arienne,

          Great job, you should be proud of yourself. Please keep me posted on how the rest of your bathroom turns out. I love seeing your progress 🙂

          Jeff

  4. Dan says:

    Hi – thanks for a great site and all the detail! Just getting ready to renovate my bathroom, and this has been the most helpful site yet.

    Quick question – there looks to be about an inch or so gap between the exterior corner of the tub, the cement board that is the back wall, and the little strip of cement board that goes down the side of the tub. Do you rely on the tile to protect from water getting in there?

    Thanks!

    1. Hi Dan, congrats on your remodel.

      My preference is to have the cement board be about 1/4 inch above the tub itself, fill that gap with silicone caulk, then use RedGard over the cement board.

      You could fill in the gap with the same thinset mortar you’ll be using for the tile installation then RedGard over the entire surface.

      RedGard is a waterproofing membrane you can roll on with a paint roller.

      If you feel like you can just use the Silicone caulk to fill in the gap go for it. When you tile over the cement board you can then add a bead of caulk between the tub and tile to ensure more waterproofing.

      Hope this helps.

      Keep me posted on your project, I’d love to see the results 😀

  5. Brad says:

    Hi,

    First off, I just found your website and you have done a great job.

    I have a question about the 1/4″ gap between the cement board and the tub lip. I did not install backer boards between the studs at this height, so I feel like caulking will be difficult. I was planning on wedging caulk backer foam the best I can in this gap and then applying the caulk. I also am planning on applying the caulk down the lip of the tub, not quite to the shelf, so that I don’t bond the tile thinset directly to the tub. I will build this caulked surface to be somewhat level with the cement board. I will then red guard the cement board and even the caulked surface. Does this sound reasonable?

    The reason for the caulk layer on the face of the tub lip is to allow for potential differential movement between the tub and the wall. The tub is on a concrete slab in my basement while atleast 2 of the walls are floating. The caulk should provide some give.

    Thanks and keep up the good work!

    1. Thanks so much Brad. When you say floating walls what exactly do you mean? I’m trying to wrap my head around your setup.

      I think you’ll be okay with the backer rod and caulking as you describe as long as your tub has a lip. Does your tub have a lip and if so, did you put the backer boards down to the lip or are they plumb and sitting down over the lip?

      Thanks buddy 😀

      1. Brad says:

        I already replied but don’t see it. Sorry if this is a duplicate.

        The studs to the walls aren’t rigidly attached to the concrete slab in my basement. Instead nails in 2×4 strips laying on the floor fit in slightly oversized holes in the studs allowing the slab to move independently of the wall. That said, the tub sits on the slab and the flanges screw into the wall studs…
        My tub has a lip and the backer boards stop 1/4 inch above the lip. The gap exposes the wall insulation. Also, the backer board sticks out about a quarter inch beyond the lip.

        I think I am going to implement a kerdi solid waterproof membrane strip over the gap and then apply the liquid waterproof everywhere else, including over the kerdi strip down the lip.

        Brad

  6. mark says:

    Is that a kohler valve you used? Does the rock need to be flush with the front of the plastic piece? And the tile would stick out beyond this? Also did you use a water membrane before doing the tiling? Thanks for any help

  7. Salman says:

    Thanks for running this web site. Question for you.
    Fixing tiles under the shower seat/bench, builder did not do a good job, they used tiles, thinset, moisture control board and dry wall. Had some mold/mildew, I have tore down this small area of 3 ft x 1.5 ft. Redoing with Cement board, the thing is I can’t move the shower frame, I am not sure how to offset the width of dry wall and moisture control board about 1 inch, whats your recommendation to use (Hardie 500 is like 0.42″) so I have to makeup for 0.6″ space. Should I use Exterior grade Plywood behind the hardie backer? Or add 1 x 2 stud on top of the frame then put Hardie backer on it? Doubling the hardie backer seems not working as I am still short 0.2″ ? Some one told me to Put Hardie board #1, then add a layer of thinset, then put another Hardie board #2, thinset, tile ….let me know your advice.

  8. Ken says:

    HI Jeff, Great tips on backerboard except it’s supposed to hang just below the lip of the tub and never have a gap above the tub lip. The way I was taught was to attach 3/16″ to 1/4″ furring strips to the studs, then 3 mil plastic sheeting so that the 1/2″ backer board overhangs the tub lip. I also us 1/4″ shims to hold the back board up off the tub deck. I don’t fur out the rest of the bath walls (but you can) but instead install a furring strip next to the edge of the backer board. This does cause a small-ish bend in the sheetrock between the unfurred stud, 16″ OC away from the furred stud next to the backerboard but I’ve never had a problem with a minor curve along the two walls that match up with the backer board. OR, I’ve seen some guys meet up the uneven drywall and backer board and after tiling, use grout to fill in the gap. I just never ever want to have even the slightest chance of water getting behind the tub and into the wall cavity. For me, caulk doesn’t cut it, but that’s just me. Thanks again for the tips.

  9. joe says:

    Jeff,
    Piecing a small section of my shower that took on water. I cut out the damaged pieces and was wondering if I can bond two pieces of 1/4″ cement board to meet the exiisting 1/2″ board?

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