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Wood Subfloor over concrete not penetrating the vapor retarder

#1
Lost the thread where JD Grafton wondered how to nail and solid wood floor over plywood on concrete without penetrating the vapor retarder. See attachment.


Attached Files
.pdf   Chap6 INSTALLING A SUBFLOOR OVER CONCRETE.pdf (Size: 233.49 KB / Downloads: 3)
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#2
Thanks for that Jim. I can't remember asking how to install a floating wood underlayment but it is an interesting read.

I would suspect a system where you would lay down a vapor retarder, say at minimum a 10mil poly, then put down 3/4" plywood and shot it right through the poly to the concrete would work. I would hypothesize a hole every 12" or so would have a negligible effect on vapor transmission through the wood.

Any idea how we could test this type of install to prove the theory?
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#3
Typically I feel the same as you regarding the amount of vapor penetration but say you were going over lightweight concrete NWFA does not feel nailing into it will hold so for solid nail down a floating floor is the way to go.
Funny all I ever hear about is plastic yet we still use 2 layers of 15 lb asphalt felt adhered with black mastic in addition to plastic. One doesn't have to figure out the permeability of asphalt.

We typically use powder gun fastening all the time BUT then we are not on the gulf coasts states. El Paso on the moisture map is rated 5 mc in wood winter and 9 mc in wood in summer. Florida is 11 and 13 different areas must be adjusted accordingly. JD notice I am getting better differentiating between mc for wood and rh for concrete. You keep me on my toes.
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#4
Some of the older flooring guys have showed me some amazing uses for asphalt impregnated felt.. I bet it would work just fine as you said.

I saw an old tile installer use it as a slip sheet over a crack in the slab. He put his ceramic right over the top. I was upset as all get-out because it was my job (I was the QC rep for the builder) but he assured me this would work. I of course wanted to use the latest and greatest crack membrane on the market.

I checked that restroom for 5 years and never saw any hairline crack at all. Now was it because of the felt or because the slab never moved?

I can confidently say I know next to nothing in the grand scheme of things.... Tongue
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#5
(03-25-2013, 10:41 AM)CC Solutions Wrote:  I saw an old tile installer use it as a slip sheet over a crack in the slab. He put his ceramic right over the top. I was upset as all get-out because it was my job (I was the QC rep for the builder) but he assured me this would work. I of course wanted to use the latest and greatest crack membrane on the market.

Look at how the decking guys & outdoor tennis court resurfacing people do cracks before coating. Really interesting. Same idea but usually with fiberglass and an epoxy glue over,under, and around.

What crack type thing were you thinking about? Cracks are a BIG issue for me. Isolating joints remains something the resilient flooring world doesn't have good answers for yet.
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#6
Cracks in concrete really. In El Paso I can look at almost any large commercial job supermarkets etc and see expansion joints or saw cuts were most look like the floors has the mumps. Along with adhesive that has emulsified especial black asphalt adhesive. Gypsum patch instead of cement based floor patch always evident.
If ever there is a need for concrete testing this is the proof. Must take some pictures sometime.
Had a high school 225,000 sf architect specified insuti testing flooring contractor didn't figure any monies for that so they are still going around and around about. Humm wonder who will win.
You got to love this one supermarket a local store hired some real low priced installers to install vct. I was called to see why the adhesive kept oozing out from the cracks. They used carpet adhesive!! Needless to say the entire job had to be redone.
Must stop this now being on the border with Mexico we get a lot of top notch installs and the horror stories abound.
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#7
RH testing is not the answer for joints. If anything it could be a good reason for CC testing. Somehow figure out the moisture profile of the slab and use that to establish the potential reverse curl and then use that as a basis for intalation windows.

Few people can get a good ASTM C157 test done pre-slab. Fewer still can get it done in a dry room not a humid room.
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