Flooring Over Concrete? Moisture Barrier?

neolitic

That's what I do.
Avoid penetrations, cause then it ain't a vapor barrier anymore

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JPhelps

according to nofma there are several ways to do it correctly. There are a lot of different methods people use and have found acceptable as well. I got one coming up that I decided I was going to use the floating subfloor method, which I think will be the easiest one(I may be wrong) But after leveling the concrete, laying out 6 mil black poly and floating 2 half inch sheets of treated ply that are attached to just each other at an angle somewhere in between parallel and perpandicular, and laying your wood on top of that, I'm excited about tryin it. I've heard it makes for a really nice walking floor. The other ones I have done the treated ply attached to the slab, which require the mastic and roofing felt because your putting holes in it. If you end in a doorway you'll have to completely remove the door and scribe the jambs to your transition, which are really easy to make with a table saw and an orbital sander. Start out with some 8/4 material, leave about a 2 inch area of the built up subfloor uncovered by hardwood where the transition will be....notch out the underside of thick material so that it lips up over the ply, and sits on the slab. then take it to the table saw and cut a slope on the face of it. You can leave about 3/8 on the leading edge, can't remember what angle I used, pretty sure I just eyeballed it. break over the edges with your sander. Transition stock needs to be at least 6 inches wide in my opinion. Sorry bout my explaining/typing, I make stuff run together horribly. You could glue these down, but what I have always done is screw and plug. I should just post some pictures on here so you could see, when I figure it out I will.

Jerry T

No one has suggested this... but just for the record "do not" use any type pressure treated plywood for floating subfloors. Even if its a KDAT (kiln dried after treatment) it's too wet to use for this.

Edger Boy

Jerry, How can it be wet if it is kiln dried?

Floordude

Prep the concrete to make it flat. Let that dry.

Asphalt mastic and a layer of 15# asphalt felt paper, over lapping the seams 4 " and sealed with mastic, as your applying another layer of mastic over that, with another layer of 15# asphalt felt paper spanning the seam below, and also overlapping the seams 4" and sealing with mastic. Now a layer of 6 or 8-mil plastic, with the seams overlapped and sealed with clear packing tape(has a good perm rating)
Now lay your sleepers out on 8" centers and don't use pressure treated, as it has a high moisture content, which will effect the flooring.

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Jerry T

I believe it is dried down to between 15 and 18%. Subfloors or sleepers needs to be down around 9,10,12% range for this use ... whatever the normal moisture level is for your area of the country.

Where I live the norm would be in the 8.5 % to 10.0 % range. I have gone into Lowes and stuck CDX and BCX plywood on the rack and have it read around 10 % MC.

Jerry T

This is an except taken from the
October 27, 2006





(appears on grade stamp).

This would pertain to sleepers but the same MC is used for treated plywood I think.

JPhelps

I agree under normal circumstances treated ply is too wet to lay on off the rack.....if you had time to let it dry in house before you layed your product that would be great. The guys at the mill where I get my hardwood have offered to let me "stick" the plywood in their kiln to take it down to a more suitable level. Though I have to agree that treated ply probably isn't necessary by the time you've applied the appropriate moisture barriers.

floorinstall

The way I've always done it and NOFMA recommends is the sleeper is glued and nailed to the concrete and the moisture barrier is laid over the top of the sleepers. If you are using 3/4 inch thick hard wood you don't have to put down a plywood sub-floor over the sleeper. To do this you have to install your sleepers 12 inch on center and each flooring strip board must span at least 3 sleeper. The end joints do not have to fall on the sleeper but staggering the end joints at least 12 inches is necessary. I did an American Eagles Outfitters about 7 years ago and there has been no complaints. By not installing plywood over the sleepers you floor elevation is not as dramatic.

neolitic

They are experts, but I don't get a vapor barrier full of holes.
Not to mention the PITA factor for not having it crawl all over the place while you wrestle the flooring into place.
No problem with nailing ¾" flooring directly to the sleepers, but I think I'll keep my vapor barrier on the bottom, thank you very much.

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