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I'm involved in the laying of a floating commercial dance floor over concrete. It needs to last 10-15 years.

The plan is to glue a layer of pressure treated wood directly to the concrete. On top of that will be a layer of 2" thick neoprene. And on top of that will be two layers of plywood screwed to each other only, otherwise floating.

Can pressure treated wood be glued directly to the concrete or is it necessary to place a barrier between the treated wood and the concrete?

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Does the concrete have water issues or could it get wet? –  DMoore Oct 2 '13 at 5:24
    
The building is new construction tilt up with a vapor barrier underneath the concrete floor. But will it still tranfer moisture to the wood? Or can the glue if applied on the whole surface of the wood could be a barrier? –  shawn Oct 2 '13 at 6:27
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What does the commercial dance floor mfgr recommend over new concrete? –  HerrBag Oct 2 '13 at 11:56
    
In my personal opinion, pressure treated lumber is for outside. Use a sill plate gasket, or other moisture barrier between the concrete and the wood. Wood should never touch concrete. Pressure treated lumber dries out, and loses its pressure treatedness over time. –  Tester101 Oct 2 '13 at 12:15
    
What purpose is the glued wood supposed to serve? Is the neoprene intended to be a sound dampener? Theoretically, your best bet would be to lay 6 mil plastic directly on the concrete, seal all the seams with tyvek tape, top with the 2-layer plywood floor laid with 1/2" gaps at 90 degrees and offset seams of second layer so as not to align with the first layer (offset by 2 feet in both directions), glued and screwed together. Plastic will prevent the moisture/condensate from reaching the growth medium (wood) for mold. –  Jacob S Oct 2 '13 at 15:07
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2 Answers 2

If I were doing the floor and not knowing what the manufacturer recommends the last thing I am doing is putting PT wood in there. The PT wood needs to dry and will bring moisture to the plywood. I know there is a lot of weight involved but I would worry about warping.

I would just swap out the PT wood for rigid foam insulation sheets - 2 inch variety. You can get really large sheets at the big boxes in the US. This will taking care of minor moisture issues and offer an escape route out. Also it might give the dance floor a slight bounce.

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If i use a sill plate gasket, will the gasket dry out. The floor has to last at least 10 to 15 yrs. The 2" neopreme is to cushion the dancers and to give back a slight spring. To make for a lively and quick dance moves. Irish dance. –  shawn Oct 2 '13 at 16:32
    
I have laid out a lot of floating floors... why the PT lumber? Where did that come into play? Also the sill plate gasket is not the solution for a large floor. –  DMoore Oct 2 '13 at 16:43
    
pt was advise from a friend, and thanks for all of your expertise, Shawn –  shawn Oct 2 '13 at 17:35
    
I would put the rigid foam under the neoprene. I normally put rigid foam then plywood on "wet" concrete environments. This would fit the same standards to me. –  DMoore Oct 2 '13 at 17:42
    
one more question. do you have to glue down the foam board to the concrete or let it float ? –  shawn Oct 2 '13 at 18:50
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New concrete (< 6mos) will have residual dampness.

You need to get a moisture meter and verify with the floor mfgr what is the acceptable upper limit.

Sealing the moisture in is a recipe for mold/mildew. The moisture needs a vapor permeable path out (not to be confused with water impermeable).

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What about a Drylok like barrier? –  bib Oct 2 '13 at 14:04
    
We do have a 1' x 4' wood. Can we use it with the sill plate gasket. We do have also so a hilti gun to secure the wood down. Sounds like ptwood is not a good idea. –  shawn Oct 2 '13 at 16:36
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