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Andras
02-12-2010, 11:29 AM
Hi,
I am building a new raised hearth for my woodstove and behind the stove would install granite tiles. Can I install granite directly over sheetrock or do I have to replace it for concrete boards? Can sheetrock bear the weight of granite? Do I need to worry about reinforcing the sheetrock?
This will not be a heat shield, the stove has its on heat shield a the clearances are satified. Do I need to worry about thermal expansion of the tiles in a 4'x8' wall as there will be some temperature change in the proximity of the stove even if this is not a heat shield?

Thanks, Andras

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Muddman
02-12-2010, 11:31 AM
I would not trust the drywall for that application. Play it safe and install cement board.

e3
02-12-2010, 12:59 PM
why wouldnt you trust it?

scrandall
02-12-2010, 03:08 PM
We (USG) do not recommend installing granite on Sheetrock on a vertical surface--only ceramic and plastic tile up to a max of 6" x 6" x 5/16" thick.

I recommend using Durock (or like CBU). Our recommendation for Durock is up to a maximum weight of 10 lbs./per sq. ft. on a vertical surface. However, I know some setting material companies have written letters of approval for weights in excess of 10 lbs./sq. ft. for vertical tile and stone installations on Durock.

Hope this helps.

Muddman
02-12-2010, 03:12 PM
why wouldnt you trust it?

Because all you are really bonding to is the paper of the drywall. And it doesn't take a lot of force to pull that paper off. Ever demo'd tile set on drywall? It's really easy. I don't like doing tile on drywall ever, but I will for things like backsplashes if it is already up.

And I don't use drywall for kerdi showers either.

Andras
02-12-2010, 04:35 PM
I am convinced now: I GO WITH DUROCK. I had this instinct about the drywall being weak (in the meantime my wife pointed out that there is layers of paint over the wall that may be the weak link), on the other hand it is extra work... . I needed a little push. Thanks everybody.

Andras

Andras
02-12-2010, 05:23 PM
Hi,

I am building a new raised hearth for my woodstove: on the concrete slab (1/16th" cracks) I am planning ditra, then a layer of 2" bricks and tile. Would the ditra under the bricks be enough for isolation of those cracks in the concrete slab? Should I put another layer of ditra on top of the bricks? since the top of the hearths could warm up to some extent (how much exactly I do not know at this point) I have some concern about the thermal stability of ditra: at what temperature would it start melting / disintegrating in the brick/ditra/tile sandwich?


Thanks, Andras

Lazarus
02-12-2010, 06:37 PM
One layer should do it. I wouldn't worry about a second layer. After the morter and tile...there is little chance of heat being a problem.

BimmerRacer
02-12-2010, 06:52 PM
I recall a thread on here about someone having some sort of problem with tile and woodstove. I do not recall the issue or if Ditra was even involved, but might be worth searching for that thread

Brian in San Diego
02-12-2010, 07:09 PM
Andras,

Welcome to the forum. I merged your two threads on this project. Please ask all questions for this project on this thread.

One thing that it's getting mentioned here is that Ditra is NOT a crack isolation membrane. They don't make that claim and it should not be assumed that it is. I don't know what the pros would think but why not build a deck mud bed instead of using bricks to form the base of your hearth? I would be severely worried about the brick over Ditra scenario. Were you going to set the brick in mortar and fill the joints with mortar as well?

I don't think melting would be a problem but it certainly could depend on how hot it is under the stove.

Oh, and by the way I installed travertine half way up the wall behind the vanity in my bathroom and it's drywall. I also installed a backsplash with glass, granite and marble in it...also over drywall. That was three years ago.

Brian

Andras
02-13-2010, 04:04 PM
Thanks Brian for consolidating the threads - it seems more complete this way.

Somehow I understood that crack isolation is the same as de-coupling. What is the difference? Since I can not use ditra for crack isolation, would nobleseal TS work? I understand that nobleseal CIS is for crack isolation but I have more than enoughf TS on my hand, would hate to by CIS unless I really had to...

For the elevated platform I was going to use concrete landscaping blocks, one foot square, 2" high, embedded in a 1/4" layer of thinset and would fill the joints after a few days with mortar. To me it seems like an easy way of building an elevated platform. I would use thinset on top then to lay the tiles. The seismic ties (needed where I live) would have to be connected to the original slab beneath the elevated platform.

As for the drywall / durock scenario: I read in some other forum yesterday (that I do not regularly read and would not be able to find again) the same scenario, that you presented, granite installed on drywall three years ago and still going strong. That is two opinions against two and my wife argument about the layers of paint on the sheetrock being weak is the tiebreaker (and how could I argue with the boss anyway), so I am still inclined to remove the wall board and go with durock.

Andras

e3
02-13-2010, 05:40 PM
TS and CIS may both be used for Crack Isolation.
Scott hopefully will stop back ,but I can'nt see what difference it would make as to the size,or type of tile so long as you stay under the 10# psf.

scrandall
02-13-2010, 08:44 PM
Eric-

The tile type and size recommendation only applies to Sheetrock. However, we know people have, do and will set granite, marble, glass and porcelain on Sheetrock, we just don't recommend it.

The recommendation for Durock is not specific to tile type or size, just the 10 lbs/sq. ft. for vertical applications. Again though, that is our recommendation, I know letters have been written by setting material manufacturers allowing greater weights with certain high performance thin-sets and Durock.

Scott

Bill Vincent
02-27-2010, 10:17 PM
Scott-- why would the size make a difference, so long as the thickness remained the same? Sorry I'm a little late to the Party, but I just found this thread through a link to it from another thread. As in the example I gave in the other thread, what difference does it make if there's one 4 foot square piece of porcelain, or 64 pieces of 6x6 porcelain? The weight per square foot would be the same.