Hardiebacker question

Dec 03, 2008 7 Replies

Greetings All, I am using Hardiebacker as the underlayment foe some slate tile. The Hardiebacker is will be installed over 3/4 T & G ply. What is the proper material to bond the backer board to the ply? It is an interior installation. Many thanks, Mark


They tell you to thinset it to the floor , then use the special Hardibacker screws to secure it. First off, what is the total thickness of the subfloor? If it's just

3/4" T&G over joists, it might not be enough. You need at least 1 1/4 " including the Hardi for a good foundation for the tiles. When I did my kitchen I ripped out everything down to the 3/4" subfloor. I then put 1/2" ply plus 1/4" Hardi and its rock solid.

They tell you to thinset it to the floor , then use the special Hardibacker screws to secure it. First off, what is the total thickness of the subfloor? If it's just

3/4" T&G over joists, it might not be enough. You need at least 1 1/4 " including the Hardi for a good foundation for the tiles. When I did my kitchen I ripped out everything down to the 3/4" subfloor. I then put 1/2" ply plus 1/4" Hardi and its rock solid.

Thanks for the quick reply, Mike. My sub is just the 3/4 ply. Unfortunately, this tile will be set level to my existing hardwood finished flooring. But, the area I'm tiling is just near a door (app 18" x 60") and my tiles are small, so any flexing will hopefully occur in the grout. The sub is very solid, so this may work out anyway.

Regardless of the thickness of the subfloor, another possibly more important issue is how well the joists are blocked or bridged. If you have access to the underside of the floor to be tiled, it's easy to determine. Blocking makes all the joists move together under loads, and done properly, will reduce flexing of the floor significantly.

bill

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hth,hand

When I wanted tile flush to the floor, I glued and screwed 3/4" plywood to the bottom of the subfloor, with 2x under it glued and nailed to the joists.

So far, no problems.

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