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Are holes in cement board ok?

10 years ago

I have found so much helpful information here so thank you in advance. The tiler who is installing wall tile in a tub/shower combo installed the cement board today. He did not put a vapor barrior behind and when I saw this I asked him to do so. He removed rhe board, installed tar paper and reinstalled the board. But, he did not reuse the original screw holes. Now I see dozens of holes where I can see straight thru to tar paper. Is this okay? What should they be filled with? He's due back tomorrow at 9 am. I hope someone can help me with this.

Featured Answer

enduring

10 years ago

I am a total DIY but here is my take on the subject. Others may have more info that can be instructive.

Those screw holes will be filled with thinset.

How was he planning to water proof the wall system if not putting something up before the cement board went on? Was he initially going to use a topical barrier of some sort? You don't want to use both. It is one or the other only.

There are two ways to provide moisture protection for your walls. One is to put on a topical paint on vapor, or moisture barrier, such as Red Guard or Hydorban, respectively. This goes on top of the cement board after it is all taped with thinset. The other is to put a poly behind the cement board. I am not sure about tar paper but I think that can be done. The thing that is important is how the paper is layered to be sure that water drains down into the shower pan and not into the wall space. It has to be lapped like siding too so that the water that gets behind the tile will stay between the barrier and the tile until it can drain into the shower pan. The other important aspect is that only one or the other type of barrier is to be used. That is, either the poly, etc, OR the paint on topical such as Hydroban. Then there is the Kerdie system that is a topical sheet product. There are a lot of products.

Comments (6)

williamsem
10 years ago
That seems odd. I just recently had my first experience with cement board. It is not the easiest thing to drive screws through, I wouldn't want to do that more than I had to! Though you do need special screws, so maybe there isn't enough grip left reusing holes?

He most likely needs to tape the seams and corners with alkali resistant tape, not regular drywall tape. I'd assume he'd use the same stuff he's taping with to fill the holes, but I'm not qualified to comment on if that's acceptable in wet areas or not..
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cinnamonsworld there is no other thickness thicker than 1/2"so that should be a clue that it HAS to be sufficient. All the other factors are what you have to look at. There are many. Can you talk about the studs? That would be a good start. Just btw and in case you wanted to know more, the Hardi company used to make ONLY 1/4" thick backerboard, and that was fine. One could buy twice as much and double it up to match existing 1/2" drywall next to the shower. I've used it, as 1/4" only. I would feel comfortable using 1/4" thick Hardi again, and for your tiles. I might add blocking. Or studs. It all depends on being there, on-site, and seeing the space. Of course, others may contradict me and tell you 1/4" is not "really" good. Not that anyone is going to throw themselves at your shower walls. Just realize that the studs and blocking are what really prevent flex. Cement board flexes a bit no matter what thickness. Using 1/4" you get a bigger shower. In a small space, this can make a difference. Studs. HTH
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The tile backer board used in bathrooms is not the same animal that was used to build your house. I'm not even sure if that material can still be found. I would use the gypsum board (drywall) which, if correctly installed, should not be obvious where it abuts the old sheetrock and do my best for a permanent fix on the plumbing. JMHO
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schicksal
10 years ago
enduring got it right. Anything moisture barrier related goes on the shower-facing side of the cement board, and you definitely do not want to have an additional barrier on the other side because any moisture that gets trapped between the two will do bad things in there. You also don't want to have any fasteners or holes in the vapor barrier but they're fine on the "dry" side of things.
mountaineer2
Original Author
10 years ago
Thank you everyone who answered. He was not going to redguard the cbu so a vapor barrier behind was vital and that's why I made him do it.

This morning he promised to redguard the left over holes to close them up. I see that all of them are in a line in a place where they will get covered in thinset.

I think it will be ok. I'll be sure to report back if there's more to report!
Bunny
10 years ago
I trust everyone who replied to mountaineer2. However, I'm having a little difficulty envisioning these layers, esp. when it comes to either/or but not both. Anyone know of a diagram that illustrates this?
enduring
10 years ago
Yes I have one of Mongoct's diagrams with regards to Hydroban. I have used this product. It is SO easy and laticrete is very reputable company.

Here is a link that Mongoct adds his diagram for hydroban:

edited to state that Mongo's diagram is exactly how I did my tile at the tub or shower in both my baths.

Here is a link that might be useful: Is kerdi-board overkill for tub surround?

This post was edited by enduring on Tue, Mar 25, 14 at 19:46

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