Building up over gypcrete??

[Switchpath]

I'm wondering if I can get some ideas on methods for going about a little project I'll be quoting for a designer we work for.

Here's the scenario:

Bathroom floor, 4' below grade over gypcrete.

A year and a half ago the previous tile was removed and replaced by a separate tiling contractor hired by this designer. UZIN PE 480 epoxy primer was used over the gypcrete. (The bulk of this lower level has 7/8" wood block installed right over this primer). In order to match the 7/8" wood block height at the doorway, 1/2" C.B.U. was laid over the primed gypcrete. Limestone tile was installed right over this, no anti-fracture.

This particular corner of the basement is right against a foundation wall which apparently wasn't waterproofed near the floor and now there is excessive efflorescence coming through the limestone and the wood block has swelled near the wall in the short hallway adjacent this bathroom. Whatever the hell the cleaning company used on this limestone also severely etched the surface throughout the floor.

The plan now is to tear out all the limestone and the wood plank in the short hall, where moisture seems to be an issue, and install porcelain. 12x12's are probably in order, assume 3/8" thick tile.

I've never confronted the need to build up over gypcrete to match the level of wood and am wondering how you guys might go about this. I have a few ideas, but would like to get your guy's uninfluenced hypothetical plan of action. Yes, I would love to tear the crap-crete out and mud the entire thing, but they may not go for this. What are your thoughts?

Thanks!

[cx]

What's under the gypcrete?

[Davy]

Well, it doesn't matter if they will go for it or not, you have to bid it so that it's done right. Then, once the Limestone and gypcrete are removed, the moisture problem needs to be dealt with.

[dhagin]

Couple things come to mind...
- solve moisture issue. figure out where it's all comin from and stop it.
- demo, then evaluate what's left. gypcrete, which ain't all that stout to begin with, may need to come out if it's been soaked for a while
- choose a system that works with what's left after demo, or demo more
- Laticrete 254 & 125 stick to gypcrete just fine, just a thought. I'd put a call into Laticrete once you're done with demo, if not sooner.
- provide general cleaning & maintenance info for your install once complete.

[Switchpath]

I haven't had an answer yet as to what is under the gypcrete. Not sure they know, and I'm not sure why it would be there and over a possible slab? Maybe just to add height on the cheap during a previous renovation?

Lets say the existing limestone comes up and without damage to the gypcrete. We can all agree installing tile over gypcrete isn't ideal but there are plenty of threads concerning the matter of prepping over it for tile. I'm well familiar with them. My main question would then be what you guys would do to build it up to the level needed including a waterproofing component?

There was a porcelain tile installed in this area for 25 years prior to the limestone. All was well, just out of date and removed along with the entire lower level renovation. It's below grade - it has moisture, too much for a limestone prepped inadequately, but not, in my opinion, too much for a porcelain. None of the drywall, door trim, or wood hanging vanity cabinet are damaged. All of which run along the same wall the efflorescence and swelled plank wood are. None of the area is actually moist, but the evidence of moisture migration is certainly there.

[Davy]

It's hard to say which material would be best until we know how thick the build up would be. Sounds like one of those jobs that will have to be decided after it is torn out.

[Switchpath]

Originally Posted by Davy

It's hard to say which material would be best until we know how thick the build up would be. Sounds like one of those jobs that will have to be decided after it is torn out.

We need meet flush with a 7/8" wood block floor that is currently installed directly on the gypcrete. So assuming about 3/8" for tile and thinset, we'll need to build up about 1/2".

[John Bridge]

Lightweight concrete under tile is not one of the things I'm in favor of. I would take it out no matter what's under it.

[T_Hulse]

Your buildup would probably be closer to 3/8" after you add a real sheet membrane for waterproofing (porcelain doesn't help, it only concentrates the efflorescence at the never-waterproof grout lines). You could cut that further down to maybe 3/16" if you used something like Ditra XL with Kerdi Band.
So it looks like a job for self leveler, except I would have zero confidence in self leveler over gypcrete, especially when this sub-standard product, which is horrible for tile, is used in an area not approved by the manufacturer.
The gyp is definitely over slab. They might have used it for a height calculation error, but probably to flatten a poor concrete job. I would educate the customers about the horrors of gypcrete, all the many ways it could fail (especially in combination with self leveler), and that it is being used against the manufacturer's wishes below grade. Bid it to tear it out. You might cut a core with your standard 1 3/8" diamond hole saw you use for shower head holes. If you mount it to a 5/8"-11 thread variable speed polisher it will have no problem cutting a gypcrete/concrete core to tell you the depths.

[Tiger Mountain Tile Inc]

I haven't followed this very closely but would it work to Ultraset over the gypcrete, install 1/2" RPM pads, and then SLU them in? It's a pretty expensive fix but I it might solve the issue.

[T_Hulse]

Ultraset is a great product, but very hard to get it to stick to dry, dusty, sandy gypcrete. You could sweep gypcrete for days and it would never stop releasing sand and dust (it's like the drypack of self levelers). That's why Custom used to want their RedGard heavily diluted for the first application over gyp, so it would penetrate and not sit on top where it could easily come right off when cured; like could also happen to a dry product like Ultraset.

[cx]

Custom still has that requirement for RedGard, Tom.

[madronatile]

Bump.

Similar situation. Gypcrete is new and is covering hydronic tubes. Not dusty at all, I think it's been sealed. Need to build up 1/2". I'd like to stick down 1/2" board with something sticky but doubt anyone would like that, since there are no mechanical fasteners. Works for membranes, though.

Have been seeing a lot more of these floors lately. Seems the standard way of installing is to pour it right to the drywall, provides the best sound attenuation this way. No perimeter expansion joint, looks wrong to a tile guy.

Is this ok? We can't do it with our mud.

[Tiger Mountain Tile Inc]

Ultraset, which is ok over gypcrete, and cbu would work I would think, but if you want a warranty I think you guys would be out of luck.

The ultraset + rpm pads that I posted above would be warrantied, I'm sure, but it get's pretty expensive.

I've tried dilluting redgard for gypcrete but didn't have any success. I could still peel it right off. I used to use ultraset for any qypcrete but have evolved into using Noble's stuff more. Usually when I run into gypcrete is in condominiums and so I use SIS.

[MDtile]

Had a similar scenario recently: new gyp over hydronic. Also no dust, it is the dense version of Gypcrete. Had to raise it to match a wood floor.

We bonded deck mud to the gyp using a slurry of Laticrete 254. Used a couple 1/2" thick pipes for screed strips, and redguarded the mud. Worked like a charm.