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-   -   How big, if any, should the gaps be between cement board when using for tile backer? (http://www.diychatroom.com/f19/how-big-if-any-should-gaps-between-cement-board-when-using-tile-backer-177081/)

Arsinek 04-13-2013 09:10 PM

How big, if any, should the gaps be between cement board when using for tile backer?
 
I saw someone saying you should have gaps between your pieces of cement board when using it for a tile backer. Is this true? If so how big should the gaps be? Also will the gap be the same size if its a cement board to drywall seam?

jsbuilders 04-13-2013 09:16 PM

I don't know why you would seeing you're going to mesh tape and thin set the seams.

joecaption 04-13-2013 09:55 PM

I've never left a gap.

woodworkbykirk 04-13-2013 09:56 PM

a gap means more crack filling and more chance of tile pops

JazMan 04-13-2013 10:13 PM

Yes, you should leave a gap so the thinset can bond the sheets together. Most say 1/8" between sheets. I believe DensShield says to lightly-butt them. I'd follow the manufacturer's directions.

The idea is to end up with a monolithic substrate, so butting them does not allow thinset to get in there. All you're doing is a surface bond with the tape, which will easily crack.

Jaz

Arsinek 04-14-2013 02:09 PM

Quote:

Originally Posted by JazMan (Post 1158677)
Yes, you should leave a gap so the thinset can bond the sheets together. Most say 1/8" between sheets. I believe DensShield says to lightly-butt them. I'd follow the manufacturer's directions.

The idea is to end up with a monolithic substrate, so butting them does not allow thinset to get in there. All you're doing is a surface bond with the tape, which will easily crack.

Jaz

I found something online that said 1/8 gaps, they were using Durock which is what Im using. This was on Durocks instructions "Fit ends and edges of panels closely but not forced together.", so it sounds like they can touch just not tightly, Ill aim for a small gap.

gregzoll 04-14-2013 08:42 PM

There should be no gaps between the panels. There is a reason why they make fiberglass mesh tape for Dur-Rock, etc.

JazMan 04-14-2013 08:48 PM

You're absolutely correct. The instructions now say as you stated: "Fit ends and edges of panels closely but not forced together." I wonder when they changed that? May have been with the introduction of Next Gen Durock.

In any case, thinset will get in there cuz the edges are not smooth, and they tell you to fill the gap: "Fill joints with latex-fortified mortar or Type 1 organic adhesive and immediately embed alkali- resistant, fiberglass mesh joint tape".


Jaz

gregzoll 04-14-2013 10:16 PM

JazMan, I have not seen any change on the instructions for fitting the panels. I am trying to find time to go next door and start tearing up the next door neighbor's bath floor, but want to get the son to do the hard work. Only catch is, that I need her to get the new toilet, and a No wax ring when I do it, so that I can pull the toilet after tearing off the old floor, then when I lay the DensShield, which I used for our bath, I can still pull the toilet before laying tile, since this is really the only bath, unless she wants to go down in the basement to use that one.

I personally prefer DensShield over Dur-Rock, since you can cut it with a knife, vs. having to use a special blade.


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