Tile over gypcrete

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  #1  
Old 02-21-09, 09:45 AM
K
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Tile over gypcrete

I'm tiling our 30 sq ft entrance way with 12x12 porcelain. The substrate is gypcrete, so I plan to lay Ditra first (with an unmodified thin set + additive), and then lay the tile over the Ditra (with same thinset + water).

My concern is with the surface of the gypcrete:

A) The surface is crumbly and chipped in places (but no chips deeper than a centimeter). Do I need to even this out somehow? Add a primer? A leveler of some sort?

B) There is a lot of old adhesive remaining on the gypcrete from when linoleum was laid down. Do I need to remove this, or at least rough it up to improve the thinset bond? If I try to scrape it off, I risk making even more gouges and chips in the gypcrete.

Removing the gypcrete entirely is not an option due to condo restrictions.

Thanks for any advice.
 
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Old 02-21-09, 11:20 AM
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Kurt

I know you dont want to hear this. Gypcrete is probably the worst substrate for ceramic tile. Its very unstable, prone to cracking etc. I avoid gypcrete like the plague.

You need to get as much of that adhesive off as you possibly can. Chemical strippers will likely make things worse.

You cannot use any cement based patching compounds or thinset in direct contact with gypcrete. You'll need to use a gypsum based patching material or leveler. I know ardex makes one. My recollection is that its called GS-4. Its a gypsym based self leveler. You need to use the ardex primer first.

You'll then need to use a primer over the leveler as well before using ditra or another isolation membrane.

No guarantees when using gypcrete. This stuff is bad news when it comes to ceramic tile.

Maxxon, the manufacturer of gypcrete has a lot of info on their website. You should start by seeing what they have to say. I know they have info and their own system for installing ceramic tile over gypcrete.

Good luck
 
  #3  
Old 02-21-09, 11:56 AM
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Originally Posted by HeresJohnny View Post
Kurt

I know you dont want to hear this ...
I was prepared for this. Every thing I've read about tiling over Gypcrete makes me wonder why I should even bother. But I've read a few success stories as well, assuming everything is prepared properly. But all the posts I've read seem to assume that the Gypcrete is in perfect condition, adhesive-free, and primed, so they skip over prepping the Gypcrete and jump right into "Apply unmodified thinset to Gypcrete + Ditra + thinset + tile."

Ardex GS-4 seems hard to get, especially in small quantities (only need 30 sq ft). I suspect the Ardex P-51 primer would be difficult to get as well. (Maxxon recommends priming with their overspray, but I assume the Ardex would work just as well.) Do you know of any good alternatives to Ardex GS-4 and Ardex P-51? Something that Home Depot or Lowes might sell?

As for adding the second layer of prime (after the leveler), should I use the same type of primer as before?

Based on your reply and everything else I've read, I think this is the plan:

1. Scrape off the old adhesive.

2. Prime the Gypcrete (with Ardex P-51 or Maxxon overspray)

3. Level/repair the primed Gypcrete (with Ardex GS-4 or alternative?)

4. Prime the resurfaced Gypcrete (same kind of primer?)

5. Apply unmodified thinset + additive. (People seem to recommend Laticrete 317 or Kerabond, but I'm going with MegaBond because it's the only brand I can find in stock and purchase in small quantities.)

6. Apply Ditra membrane

7. Apply unmodified thinset + water

8. Apply tile

9. Pray

Anything else I might be overlooking?
 
  #4  
Old 02-21-09, 12:55 PM
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I don't know of any other gypsum based levelers or patching compounds. The ones I use are all portland cement based and cant be used over gypcrete.

I'm not all that familiar with the laticrete thinsets, but I think the megabond is a low end dryset mortar. The 317 would be a better choice. If you have any tile stores around that sell Tec products, their Full Set Plus is a good choice also.

Schluter recommends unmodified under the ditra and over it for gypcrete. See page 11 of the ditra handbook on Schluter's website.

Everything else in your plan looks good.

9. Pray
This might be the most important step.

I saw you posted at the ft forum also. Theres some good people over there that should be able to give you some answers as well.
 

Last edited by HeresJohnny; 02-21-09 at 01:28 PM.
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