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I have this layout and all the areas marked with green will get tiles I am not sure about the area around the window (marled with diagonal green lines)

The area I have doubts about is the area above the green line at the bottom of the mirror. I have cement boards that would cover that entire wall (2 sheets less than 8' long)

From what I am reading the cement board could be painted over, or more accurate said, certain types of cement board

What would you recommend me to do in this case ? Should I transition to drywall in that area behind the mirror ?enter image description here

isherwood
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MiniMe
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4 Answers4

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You can skimcoat it with drywall compound (mud) and then paint.

You can also just paint it but it will look very different from paint on drywall.

Ecnerwal
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  • Cant say I like the idea of mudding and sanding the cement board – MiniMe Aug 29 '21 at 20:48
  • A skimcoat is a simple task. It's the same process done by anyone restoring old walls with damage or obsolete texture. Perhaps your concern stems from the fact that you do "mudding" and not "drywall finishing". :P – isherwood Aug 30 '21 at 16:15
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    I would rather frame a 10 foot wall then skimcoat a 6'x6' area. The idea of skimcoatting and sanding properly is not a novice task. Maybe its me but I hate it and notice every ridge. Didn't you just skimcoat a ceiling in one of the rooms in your house? – DMoore Aug 30 '21 at 17:35
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You do not need to protect the entire bathroom with cement board, no.

However, the cement board and tile should extend past the tub/shower at least a little bit so that drywall isn't the first victim of excess water splashing out.

Per:

Notice how the tile goes past the glass door.

enter image description here

If you did cement board the entire bathroom then you could apply drywall on top of it and end up fairly flush with the tilework. You will of course have to use cement board screws to attach the drywall so things could get expensive. You'll still want to extend the tilework beyond the tub-shower for the aforementioned reasons.

isherwood
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MonkeyZeus
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  • I'm not sure I follow your reasoning. The cement board could stop short of the tile edge in the case you present to simplify finishing. Also, it's not clear why a person would use cement board screws for drywall. – isherwood Aug 30 '21 at 16:28
  • @isherwood If you're putting drywall on top of cement board I would imagine it's a bit difficult to penetrate the cement board with drywall screws. – MonkeyZeus Aug 30 '21 at 16:44
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    I don't think so. That stuff is actually quite soft (porous). – isherwood Aug 30 '21 at 16:45
  • @isherwood Well in that case wouldn't the cement board corrode every single drywall screw into failure? – MonkeyZeus Aug 30 '21 at 16:47
  • Hmm I like the idea of getting flush with the tiles by adding drywall on top of cement board. The question is ...will it be flush? In particular for my project that wall requires some attention as due to error when I did the plumbing for the shower drain my shower base is now 1/2" off the framing on that wall so I need to shim like 1/4" in order to have the cement board sitting on top of the flange. – MiniMe Aug 30 '21 at 16:51
  • @MiniMe If your goal is for the wall to be flush with the tile then it would be much cheaper to double up the drywall instead of cement boarding everywhere; cement board is 2x the cost of drywall and the screws are expensive. Cement board will corrode regular screws into failure. I believe thinset is usually 1/8" thick so add the thickness of your desired tile to get your drywall calculation. Doubling up half-inch drywall might be right or you might need 1/2" + 3/4" to make it flush. – MonkeyZeus Aug 30 '21 at 16:58
  • I already bought the cement boards, maybe too many of them, it will be a PIA to return them ..and I also bought a box of these https://www.homedepot.ca/product/cgc-durock-screws-for-durock-cement-board-1-1-4-in-200-screws/1001341803 It seems that I need to go back to the drawing board to plan my cuts and my transitions and the layers that you suggested as well to see if it would work that way. It might save me the shimming if I put cement board in the mirror area. I will have to use it anyway below that as I would like to tile ...let me do the maths to see how I am doing with tiles as well – MiniMe Aug 30 '21 at 17:12
  • @MiniMe That's your call. The other consideration is that those 1 1/4" screws won't be long enough to penetrate at minimum 3/4" into the stud. You need at least 1 5/8" screws to secure the second layer on top of the first. – MonkeyZeus Aug 30 '21 at 17:18
  • @MiniMe Also, using cement board everywhere will make electrical work that much more of a pain. An oscillating tool will help but you might eat through a few blades by the time you're done. – MonkeyZeus Aug 30 '21 at 17:20
  • I have no electrical outlets on that wall. I guess 1 1/4" won't do it if I add drywall over cement board. I am seeing one more problem with this layout...the two materials have different behavior when taking water ... I have to decide if it is worth tiling behind the mirror and above it, in each case I can use the cement board on that entire wall as planned. I will use cement board around the toilet so I might not waste cement board if I cut is short after I covered the shower – MiniMe Aug 30 '21 at 17:25
  • @MiniMe These sound like questions only you can answer =) – MonkeyZeus Aug 30 '21 at 17:30
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You can finish cement board just like drywall. It's a little more difficult due to the rough texture, but a couple skim coats and you're all set. Keep in mind that the use of regular drywall mud over cement board would defeat the purpose of using cement board for those locations. Use setting-type joint compound where you expect regular moisture.

That said, I'd transition to drywall anywhere I'm not tiling--ideally just inside the edge of the tile. This makes finishing easier, not to mention installation. Cement board isn't fun to work with. A quality primer and topcoat will alleviate any occasional splash concerns.

isherwood
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The other answers are more or less right but missing some important details.

  1. You do not want exposed cement board to extend out. The goal should be for the tile - even 1" - to lap over the drywall next to the cement board. Remember you don't need cement board outside your doors and things like that.

  2. What if you have to have "exposed" cement board. Yes you skim coat it. But if you use latex pva primer and latex paint - which most people on here would suggest - your skimcoat will crack and fail within a couple years if that long. You must must must use an oil based primer to provide a moisture barrier for the 1/8" skimcoat. After that you can go latex or oil on top of it.

After finishing over 100 bathrooms I can say the #1 thing to longevity of the look and feel is using an oil based primer. It is funny your question is exactly why I started using it. We got these shower kits that were thin sheets of marble (not faux marble). Everything had to be almost exactly plumb/square and called for concrete boards backing... We just decided, so there wasn't a gap to run the boards to the ceiling (~9') when kit was about ~6'.

So skimcoat the upper area, prime, paint. Every fricking unit that we did this bathroom - paint/skimcoat failure. Older guy in our crew cleans up the first one... Asks me what type of primer. Explained to me how oil based primer prevent steam moisture from penetrating. Reduces these kinds of issues, nail/screw pops, wet spots and almost every other kind of bathroom issue. Never primed another bathroom in latex.

DMoore
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  • I have basically fallen in love with using Gardz (or Draw Tite if you can find it) when sealing new mud. It binds and reincorporates any residual dust and prevents any re-wetting. – Matthew Aug 31 '21 at 01:37
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    @Matthew - I have used Gardz too. We have tested this. I can spray a wall done in oil primer and paint with a hose and dry it off and it is bone dry in 30 mins. You do that with latex and no crap the mudding may fail on the spot. There should be more requirements for semi-wet (steam) locations. It's not magic but it helps prevent 95% of the small issues bathrooms get with steam and water. – DMoore Aug 31 '21 at 16:33