radiant heat

Bob Gagnon plumbing and heating

is what i was refering to. do you just use a few screws and allow the cement board to float?

Bob Gagnon plumbing and heating

quick set mortar over quic-trac

is that o.k.? i have a contractor that wants to put the quick set on top of the quick trac, to hold the cement board down, with only a few nails. thanks, bob

Earthfire

cement board

I would use thinset tile mortar. It is what is recommended by the board manufacturers to laminate cement board to plywood,cement, tile and just about any sound substrata. I don't think that a quickset spread as thin as you would use to glue cement board (1/4" notched trowel) would give much of a working time.We also use the cement board screws, easier to get through the board then galvanized deck screws.If the cement board isn't attached properly the tile will start popping loose or grout cracking and "that damned no good radiant heat system"will be at fault,not the shortcut Cement board install. Journal of Light Construction has published some informative articles on tile installs and problems that have poped up. I think that they are available in their archives.

Earthfire

cement board

I like Durock brand cement backer board .( Not recycled newspaper stuff like Hardibaker) Available in several different sizes Basic 32"x 60" available at home centers in the drywall dept. Larger sizes available at real tile supply houses and specialty drywall steelstud suppliers.Its rated for indoor and outdoor exposures. There is a fairly specific fastening schedule on the label. On floors we thinset then screw. We use 8" + -centers and about the same on the edges. On walls we use subfloor adhesive and screws to the studs. With thinset there is no float it is fully adhered if done correctly

Mike T., Swampeast MO

When attaching the cement board to a dissimilar substrate like wood, use either polymer-modified thinset or acrylic-latex admix when mixing "plain" thinset.

The alternative is a "cleavage membrane". Such sounds great in theory, but is VERY difficult to detail properly in practice.

While still quite new, ceramic tile over properly applied cement board seems to be exceptionally durable--possibly even better than the traditional "mud job" that it claims to replace. A good mud job is still probably the gold standard, but often the structure cannot support the extreme dead load. I work on old homes and have seen some truly bizarre constructions to hold mud jobs (like floors "hanging" from rafters via iron rods and wild framing to spread the load) but all seem to have failed quite rapidly.