Question on concrete board

[Oppie]

I'm remodeling a very small bathroom (about 5'x7'). For now, I'll just be laying linoleum, but I would like to lay some concrete board so that I can at a later date tile the room. The flooring right now (under the existing linoleum) is a 1/2" thick plywood. It seems very solid and doesn't seem to buckle. This house was built some 40 years ago and the wood looks in excellent condition.

Anyway, how THIN of a layer of concrete board can I get away with? I don't want to raise the final level of the floor any more than necessary. Would 1/4" concrete be okay for a small job like this?

Thanks!

[Edwin Pawlowski]

See what the tile maker says about their product. I don't know that it is even available that thin. If it flexes, the tile will crack.

[Oppie]

Yeah, I don't really know what sizes it comes in. I think I've seen it in 1/4" but maybe I was looking at something else.

From what I've been told elsewhere, better to be safe than sorry. Damn, I really hate lifting the floor up that much. Oh well!

[Cliff Hartle]

It does come in 1/4" thickness, but it will probably flex too much. Even a miniscule amount of flex will crack the grout.

The thinnest I have read you can go for floor thickness is 1/2" durarock attached to 5/8" plywood using thinset and the proper type and number of screws.

When I worked for a construction company I put down a dozen or more floors and always had to come back and try to fix loose tiles and cracked grout on floors where the sub floor wasn't thick enough.