# Concrete backer over 1/2 inch subfloor



## jim20 (Aug 2, 2007)

Does anyone know if it is possible to install 1/2 inch concrete backer board over 1/2 inch plywood subfloor or should I use another layer of 1/2 inch plywood .


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## Cole (Aug 27, 2004)

When it comes to underlayment for tile, you always want to go bigger.

Personally, I would go another layer of 1/2".

What size joists do you have?


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## ChrWright (Jul 17, 2007)

1/2" ply will give way too much deflection...Your assumption is right on...Add another layer of 1/2", then the cement board.


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## JazMan (Feb 16, 2007)

Single sheet subfloor have to be at least 5/8" thick if the joists are 16" o.c. or less. Even this is crap, but it does meet minimum standards, for those that will accept the very minimum. :no: Make sure you off-set the second layer of plywood from the first, and lots of 1 1/4' screws.

Jaz


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## reveivl (May 29, 2005)

This post is meaningless, and the answers even more so, unless you provide more information.

What are you going to put down? Tile or stone?
What are the joists?
What are the dimensions of the joists?
What is the span of the joists?
What is the joist spacing?

There are two issues that are critical for tile/stone: joist deflection and underlayment deflection between the joists. Without an understanding of all of the above questions you cannot decide whether or not your floor will support adequately for tile or stone.

Be aware that concrete backer board adds nothing in terms of support, it is there to separate the tile from the wood with their different thermal/moisture expansions.

1/2" subfloor, I wouldn't use less than 5/8" over that, then thinset then cbu, thinset and tile. For stone you'll need more.


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