I have been asked to set tile for two shower stalls.
The GC used concrete backer board for the walls ( 1/2″ Durock), and he had his taper mud the corners and seams with fiber glass tape and regular joint compound. He claims there should be no problem getting the tiles to adhere with either mastic or thin set.
I feel strongly that the tiles should be set with thin set, and I have three questions:
1) Is he right (that setting tiles over joint compound is no problem)?
2) Could I get by with with scraping removing as much of the joint compound as possible, and then using fiber glass tape and thin set over the joints and corners?
3) Or should I insist that the CBU be torn out and we do it over again, this time taping the joints with thin set?
The owner is a good friend of mine, and I want to be sure the job is done right. And the GC has dug in his heels on this one.
I would be grateful for your feedback.
********************************************************
“It is what we learn after we think we know it all, that counts.”
John Wooden 1910-
Replies
If it is regular joint compound, not the durabond setting type, it will get soft and mushy in the presence of moisture.
Do you have enough room to add a layer of 1/4" hardiebacker? Might be easier than removing the jc.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Taping compound should come right off with water and a scrub brush. If you can get back down to clean CBU then you're all right. But, who knows what sort of moisture barrier this clown put over behind it?
Well, he's right that the tiles will adhere with either mastic or thinset- it's really more a matter of how long they'll "stay adhered"....
Definitely use thinset- mastic is a bad idea in a shower stall. You could "probably" leave the joint compound, but to do it right, scrape out as much as possible and replace with thinset.
Bob
My guess is that he was lazy and had a bucket of jc at arms reach. Seems like a real dopey thing to have done. Why would you use a "cement" board and use jc on it. Ask him if he uses jc when he lays brick too...lol.
Like David said..it'll come right off with some warm water....which is the point here.
By the way...I don't even use water in my mud on the fiber tape or tile mud...I use a liquid latex additive.
Be safer then sorrier
andy
The secret of Zen in two words is, "Not always so"!
When we meet, we say, Namaste'..it means..
Thanks for the quick responses.I happen to know the CBU was installed directly over the studs -- with no membrane, builder's felt or anything else. That too didn't seem smart to me, but I have seen that done a lot.********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
You can get a trowel on water proofing material to put on top of the CBU.
Now the pan is suspect, too.
Actually, the entire installation is very suspicious.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
For the immediate problem, I would use a trowel on waterproofing like Laticrete 9235.I would ask the contractor if he did a pre-slope, and what the membrane is.I really don't like this contractor."I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
This could get ugly; but the GC will be there tomorrow, and I will see what he has to say. I am grateful for all your opinions. What I'd like to do is scrape/scrub off as much of the joint compound as I can. Then redo the joints and corners with fiber glass tape set in thin set. Does that seem the most reasonable approach?********************************************************
"It is what we learn after we think we know it all, that counts."
John Wooden 1910-
Without waterproofing I would not touch it. Read up on the various trowel-on waterproofing products including 9235 and decide whether or not you could warranty the install.
Or have the GC warrenty the install, since he has "dug his heels in" on this one.
Get him to sign off on a 3 to 5 yr. warrenty period, and see how quickly he'll loosen up.
Most of those clowns get past their one year limit on liability easily enough, or are able to dump the issue on the poor sub that was installing to the GCs' specs to start with.
I've been the that poor dumb sub on at least two occassions. I would walk on any of them that expect me to be liable for tier poor building practices.
Dave