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Unread 08-08-2013, 11:30 PM   #1
madronatile
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Tiling over cracked gypcrete

Hi all, been awhile, hope everyone's well.

This one is way outside the box, not worried about installation instructions or warranties, guarantees, disclaimers.

Builder wants us to tile over old cracked gypcrete. Big cracks, like almost 1/4". Some have already been filled at some point in the past with some compound. Knocking on floor produces different tones on different sections. Demoing it all is not an option.

1.5" gypcrete over plywood over joists.

Plan proposed is to redguard the gypcrete, 4:1, then a full strength coat. Then fasten 1/4" cbu over top with 2.5" screws, followed by Laticrete 170 sound mat. Then Nuheat cables, thinset, and 12x24" porcelain.

Any thoughts or ideas on how to make the best end product out of this less than ideal situation would be appreciated. The 170 is required.

THanks!
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Unread 08-08-2013, 11:45 PM   #2
Screw Loose
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1. Why is it not possible to demo the existing?
2. Why RedGard the gyp IF you are planning to put 1/4" CBU over it?
3. Screws, unless pre-drilled will probably further blow the gyp apart if it already has cracks.
4. The existing gyp, then your plan seems like an excessive build-up in a situation where it sounds like there's already movement/deflaction. Have you checked defelction on this?

Thinking on #2, you'd need to BEST possible adhesion between the gyp and the CBU with quality mortar. IF there's a moisture issue I'd think that the RedGard would then go ON TOP of the CBU.

Since this already sounds like a Frankenstein nightmare, have you thought about instead mortaring down metal or plastic lath to the floor to then set your heat cables and sound mat? You'd save a tiny amount of build-up, but reduce the weight by skipping the CBU, plus not risk blowing apart the gyp with a bunch of screws.

But I could be totally wrong.
Got any pictures?
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Unread 08-09-2013, 07:10 AM   #3
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What Christian said about the screws plus the cost of the screws would be considerable.

Time for a new (equally bad) plan.

Glad I'm not on this job.
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Unread 08-09-2013, 12:58 PM   #4
madronatile
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They don't want to remove it because it's a condo and for whatever reason anything sound reducing must be replaced in kind. Also it has framing on top, some of which is party wall. So they're nervous about cutting it close to the plates and getting in trouble with neighbors.

New gypcrete or marmoleum is apparently not an option, but total failure is a risk they are willing to take.


The thought with the redguard was to keep any moisture out of the gyp.
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Unread 08-09-2013, 07:38 PM   #5
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This is a crazy one.

I wonder if slu would be preferable to cbu in this situation. At least it could run into the cracks and fill things in?

I'll throw out an alternative idea: skip the cbu and fasten 1/2" plywood down instead. Route out 1/4" deep channels for the heat wire and sound proof over all of it. (I'm thinking the plywood would be embedded into something- thinset? slu?)
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Unread 08-09-2013, 08:05 PM   #6
The Kid
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Fasten expanded lath over the gyp, slc, 170, tile.

Prime the heck out of the gyp of course.
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Unread 08-09-2013, 08:15 PM   #7
ceramictec
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and you wonder why the old gypcrete is cracking.
possibly subfloor movement.
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Unread 08-09-2013, 08:35 PM   #8
The Kid
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Tie all the loose gyp togethet with lath and slc and it will be like an unbonded bed.
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Unread 08-10-2013, 12:51 AM   #9
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Blue or white duraweld glue and plastic cement or dry pack is my 2 cents. Felt or adhesive roofing membrane for floating isolation.
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Unread 08-11-2013, 05:50 AM   #10
Brad Denny
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If this were mine I'd look at two options...

1. Ask building management/owner for the original prints/specs for a name on the old gyp. Build a new system meeting the same IIC using a mortar bed. Cutting 6" off the party wall is better than leaving the whole thing IMO.

2. Skim/fill cracks with 254, Hydoban, install with 125. I haven't used 125, but I've heard good things about it.
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Last edited by Brad Denny; 08-11-2013 at 12:06 PM. Reason: Steve corrected my thoughts!
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Unread 08-11-2013, 06:20 AM   #11
Steve in PA
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Might want to look at Laticrete 125 as it can kill all three of those birds (bonds to gypcrete, crack and sound suppression) with one stone.
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Unread 08-11-2013, 10:04 AM   #12
Foochacho
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Wonder if cork underlayment put down with a good urethane glue would help.
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Unread 08-12-2013, 09:05 PM   #13
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Run, don't walk, as far away as you can get from this. It isn't worth it.
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Unread 08-13-2013, 12:41 AM   #14
Higher Standard Tile
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We had one like that. We removed the old gypcrete and installed an 1 1/2" thick wire reinforced mud bed on top of plywood and Ditra on top of that.

The old gypcrete had been poured over single layer plywood with no primer or wire. No wonder it was all cracked and hollow.

Cut a joint as close to the walls as you can so the framing is not affected when you remove the gypcrete.

There is a lot of that type of material in the low rise condos out here. I avoid them when possible. The last few I have bid high enough that they just called someone else.
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Unread 08-13-2013, 04:02 AM   #15
Lump
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Ardex makes a product for gypcrete like this. Will look for it.

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