I live on the third story of a 5-story condo building, and our
Homeowners association requires that we put a specific cork sound
barrier down under any hard floors we
install--http://www.amorimsolutions.com/acousticork. So we are having
1000 square feet of porcelain tile installed over the Acousticork R60
6mm cork which is on top of our concrete underlayment and that is all
fine and good. The problem now is with the sanded grout we are using
http://www.tecspecialty.com/ with acrylic grout additive that our
installers have used many times with success. But in our case, they
have grouted a small area, and after several days, it still seems to be
flaking off- just not very hard like it should be. We can scratch it
out fairly easily with the grout removal tool, much easier than with
the grout in our bathroom which has been there for 10 years. On top of
that, the installers said they test jumped on it and the grout is
starting to show crack lines.

Now our installers are saying they've talked to a more experienced tile
installer in town, as well as some kind of National Tile Association,
and both have told them we need to put epoxy grout.

My question is, has anyone out there had to use cork underlayment under
a tile installation, and what type of grout did you use? I'm a little
against using epoxy grout, I don't think it should be necessary in a
condo with only two people living there, and it's such a toxic
chemical. I would like to find out if normal sanded grout with the
acrylic should be okay, and maybe something else is causing this
problem.