Backerboard over Subfloor


Old 05-05-07, 07:21 PM
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Backerboard over Subfloor

I am putting down cement backerboard (actually Hardiboard) to eventually lay tile. The hardibacker is going over an existing plywood subfloor. The installation instructions for the hardibacker indicate that I need to lay mortar to attach the hardibacker to the subfloor. Additionally, I need to put about 40 screws per sheet into the board to secure to plywood subfloor.

My questiona are 1) Do I really need to cement the backerboard to the subfloor given all of the screws that will be going into the backerboard. 2) If I do need to cement, what is the purpose of cementing and screwing?

Any thoughts would be greatly appreciated.
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Old 05-06-07, 03:27 AM
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Placing the thinset on the floor prior to the hardibacker will aid in adhesion and will also tend to self level the floor and prevent dead spots. A good part of the hardibacker is they indent the panel everywhere you need to put a screw. Sort of a neat innovation, IMO.

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