- Q.I want to install a thin
radiant slab over a wood subfloor in a remodel. The
flooring will be ceramic tile. What is the thinnest
slab I can get away with?
A.Heating contractor Bill
Clinton responds: If you want a slab as thin
as possible and expect to tile over it, I think
regular concrete is out of the question.
You’re bound to get cracking, which will
telegraph through the tile. My choice would be a
gypsum-cement product — either Gyp-Crete
from Maxxon Industries (800/356-7887;
www.maxxon.com) or Gyp-Span from Hacker Industries
(800/642-3455; www.hackerindustries.com). Gypsum
cement, unlike concrete, doesn’t shrink as
it cures and usually won’t crack. When it
comes to preventing cracks, the most important
factor is the rigidity of the floor framing and
subfloor.
Gypsum cement can, with care, be poured as thin
as 1 1/4 inches. You can thin-set the tile to a
gypsum-cement slab. But before tiling, you need to
allow the gypsum underlayment to dry completely,
and then seal it. In bathrooms, you will need a
waterproof membrane, like NobleSeal (800/678-6625;
www.noblecompany.com).