gypcrete on condo floor

I have gypcrete on my condo floor. I took up the tiles and found a somewhat crumbly cement type stuff. The tile came up very easily. What is my next step. I want to put down slate, do I need/can I use Hardibacker or can I put it on the gypcrete?
Thanks,
Jones

 

No cement board over gypcrete. Gypcrete and thinsets don't mix as thier is a chemical imbalance between the two and gypcrete will absorb the moisture out of the thinset preventing a proper cure and the moisture in the thinset that wicks into the gypcrete can cause the gypcrete (gypsum based cement to not get too technical) to fall apart. Then their is the issue I mentioned in the last thread about sound control under hard surfaces in upper level condos. Your first step before proceeding is to contact your condo association (who has the right to make you take it all out if they have sound control requirements that are not followed) and see what they require. Some can be glued down over the gypcrete, or you may need to pull out the gypcrete, and install ply, backer (for fire rating) and soundproofing underlayment, or if their are no guidelines in place, their are membranes you can use over top of gypcrete as a setting bed. 3 that come to mind (I run from condo jobs if I have to leave the gypcrete) are Noble Company's CIS glued down with their special adhesive, Schluter Ditra set with rapid setting mortar, both of which are roll type membranes. Another option would be Redguard from Custom Building products, which gets applied with a garden sprayer 40 sf/gallon of a 4-1 mix of water and Redguard, and then fullstrength Redguard rolled over the gypcrete with a 3/4 nap roller 45 minutes after priming. The later method is only able to be used if the gypcrete is "gypcrete 2000" which means the compressive strength of the gypcrete is at least 2000 psi. Whenever gypcrete is poured, core samples of the gypcrete are taken from the job site and anyalized. The compressive strength of the core samples should be available from the condo association. Go see your condo association and then post back. Condo associations---GOOD LUCK

 

I won't take a job if Gypcrete is on the floor, too risky no matter what you install over it, even if they warrantee it, the membrane manufacturers that is, don't need that phone call.

 

I always, always, always use Ditra over Gypcrete. Always.