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07-18-2006, 05:55 PM
I want to install 12x12 ceramic tiles above gypcrete. The subfloor is .75in osb with 1.5in gypcrete. The gypcrete was poured 2 weeks ago on the second floor of a 4,200 sqft 5-unit building. This is my first encounter with using concrete indoors. It's being used as a sound barrier in this project - no heating elements in the floor. I'm on Washington's Olympic penninsula, 3 blocks from the pacific ocean. It's sunny in the 70's now but it's moist (rains) here in the winter (almost all the time). It's new construction.

The tile will be installed in some bathrooms (about 60 sqft each) and 2 kitchens plus entry (about 120 sqft each) and a common hallway (about 80 sqft). These units are for me to keep so it's a DIY project and installing the tile will be a new experience for me.

o I'm planning on rolling Redgard on the concrete and then thinset/tile on top of that. Am I missing a layer of anything?
o Can anyone recommend a moisture meter for testing the gypcrete (hopefully a cheaper one)? Are there any meters that can measure wood and concrete?
o I'm leaning towards Redgard instead of Laticrete 9235 between concrete and tile because no heater under the gypcrete - does this sound reasonable?
o What kind of thinset should I be using for this application?
o Spacer size? The tiles are almost flat edged - tiny bevel. I'm thinking 1/8th or perhaps 1/16th gap. What issues/problems should I be aware of using smaller spacing?



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Rd Tile
07-18-2006, 06:02 PM
I would highly suggest a sheet membrane over gypcrete, it's not exactly concrete, read up on Ditra and Noble membranes and see which would work for you, as for spacing, depends on how even the tile size is to one another.:)

07-18-2006, 06:37 PM
Mini Ligno for the moisture meter.($100) Do not install that tile right on the gypcrete.

Mountain Tile
07-18-2006, 06:51 PM
Ditto, do not install tile directly on gypcrete. You basically have two options. mud bed or a sheet membrane. I would rule out mud for reasons of height and weight. I would say ditra would be a good way to go. But that is just my opinion. :goodluck:

07-18-2006, 07:45 PM
potential problem with thin-set and Gypsum....check with the mfg. of the thin-set..
Noblebond 21 and Nobleseal over Primed Gypcrete no problem.

07-19-2006, 03:22 PM
Thanks to all for responding.

I thought from my reading that Redgard or Laticrete 9235 were supposed to work as a membrane between gypcrete and tile. Was I mislead on this?

This is the first time I have heard about Noble products so I looked at the NobleSeal CIS with NobleBond 21. Looks like about $2/sqft. Ditra seems like overkill but since I'm a complete newbie I have no way of really knowing.

Help me get smarter:

When looking for products that work with gypcrete (since many just say they work with concrete), what are the most important properties of gypcrete which differ from regular concrete that the inexperienced DIY could get into trouble with?

What typically happens to gypcrete that can cause a failure with tile that the membranes solve?


Mountain Tile
07-19-2006, 03:46 PM
Gypcrete is a gypsum based product, it's lightweight and for sound proofing, does'nt have much strength. I have a freind who installs carpets in condos alot, usually he'll tear the old carpets out and there is the gypcrete all cracked out. And it will have to be replaced before he can come back. And it might not even be that old. you need some type of reinforcing (lathe in a mud job or a sheet membrane like ditra) without it your doomed to failure. :shades:

07-19-2006, 04:25 PM
>>Mini Ligno for the moisture meter.($100) Do not install that tile right on the gypcrete.


It looks like there are a number of different Mini Ligno models. Which one were you mentioning?


07-19-2006, 05:02 PM
THe one that is standard I think. ITs got a switch that goes between wood and concrete, some LED's and 2 probes. That evague enough for you?


07-19-2006, 05:06 PM
THis is the one:

07-19-2006, 05:34 PM
Note that Eric said over Primed Gypcrete

07-19-2006, 06:20 PM
What typically happens to gypcrete that can cause a failure with tile that the membranes solve?Cracks. Lot's of 'em. Gypcrete is typically poured with no expansion joints at all, even in the doorway. So at almost every outside corner or doorway you can expect cracks, plus at many other random locations.
Liquid style products like Redgard & 9235 are great, but one problem with gypcrete is that the very top layer is extremely weak & can easily separate from the sandy body below. It's better to have a sturdier sheet membrane that can contribute to the "substance" of that top gyp layer and discourage debonding.

07-19-2006, 07:42 PM
Again, thanks for all the help.

Thanks bobturner for pointing out the exact model to buy.

Thanks T_Hulse for the detailed explanation. You have convinced me that a sheet is neccessary. In my building design there are double plates under each wall and only the top plate was cut at the doorways. So in my case, the pour in every room is isolated and the gypcrete should be more stable that way. FWIW, the company who did the pour told me that gypcrete doesn't shrink or crack. Was he fibbing to me?

>>Noblebond 21 and Nobleseal over Primed Gypcrete no problem.

What is used to prime the gypcrete?

07-20-2006, 10:22 AM
I just watched the install video for Ditra and I'd have to say it looks really simple and straight forward.

My bathrooms have curved tubs. Is it pretty easy to cut the ditra to fit?

07-20-2006, 04:42 PM
Was he fibbing to me? if he really believes that you're in big trouble. :D

I would recommend you contact the mfr of the gypsum probably Maxxon or Hacker. They both have websites. That way if you have problems you have a leg to stand on.

07-21-2006, 09:22 PM
FWIW, the company who did the pour told me that gypcrete doesn't shrink or crack. Was he fibbing to me?Nope, he wasn't fibbing. He was lying, and that was a real whopper. Gypcrete always cracks.