Can't you decrease deflection with plywood? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-03-2004, 06:10 PM
According to:

With all of this being said, it can now be understood where the recommendation for two layers of plywood 5/8" (16 mm) thick or the use of other underlayments, is required by the TTMAC manual, Detail 313 F-98. Other underlayments such as " 13 (mm) cementitious backer board, or a pre-formed sheet applied membrane such as Schluter Systems, Ditra Matting can be considered.

My understanding of this is that two layers of plywood or the use of other underlayments are required by TTMAC manual to decrease deflection.

Our contractor (and others) are suggesting that adding another layer of plywood will decrease deflection.

Isn't this also what TTMAC is saying?

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Rd Tile
08-03-2004, 06:35 PM
Depends on where the deflection is, between the joists or the joists themselves.:)

Plywood only helps the span between the joist.:)

John Bridge
08-04-2004, 04:21 PM
What RD said. :)

At Tile Your World we start by checking out the joist system. That's what our deflectolator does. When the joists pass muster we address the subfloor.

Say you have joists that are over-spanned and bend down in the middle when someone walks over them. You can't fix that by doubling up the plywood. You have to double up the joists or shorten the span by adding a beam or something.

08-04-2004, 04:53 PM
What JB said. :)

Rd Tile
08-04-2004, 05:02 PM
What CX said.:D