Subfloor strength

18 years ago

I am putting a stone floor (1/2" soapstone, 12"x12") in my bath. The house is 60 years old, pier and beam foundation. The floor joists are 12" on center, 2"x8" with 9' spans. Extensive plumbing rework required removing the original angled-decking subfloor over everwhere except under the tub (where the new walk-in shower will be) -- a 7' x 8' space, where the stone floor will be.

Here's my questions: the GC proposes to put down 3/4" decking plywood as the new subfloor, followed by 1/4" hardiebacker in thinset, etc. Will that be strong enough?

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Comments (3)

bill_vincent
18 years ago
3/4" followed by 3/8" plywood and then either 1/4" cement board or Ditra.
bradleyj
Original Author
18 years ago
THX -- you the man! Its what I thought (John Bridge said the same thing) but wanted something to show my GC who is wanting to renegotiate the price b/c I want things done "above standard" (including setting the CBU in mortar rather than just nailing it down, and no 1" gaps at greenwall joints of ceiling to wall or wall to wall in the nonshower areas)
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bill_vincent
18 years ago
Sounds to me like it's time to find another GC. If he's shortcutting things like this that CAN be seen, imagine what's going on "behind the scenes". None of what you've mentioned is "above standard". Every single CBU manufacturer DEMANDS that their product be set in a bed of thinset, in addition to either screwing or nailing it down. The thinset isn't there to bond it to the subfloor. It's there to cushion it, so as to take out vibration between the two layers. As for the two layers of plywood, It's actually SUBstandard to TCNA specs. The spec actually reads 1 1/4" of plywood in two layers PRIOR to CBU for natural stone.. However, it's fairly common to go with 3/4" and 3/8" with no ill effects. As for the gap in the sall board, that pretty much speaks for itself.