Vapor barrier between carpet and slab?

WVBill · Dec 3, 2004

My wife's Quilt Shop has a 19' x 14' room attached to the back - an add-on to the original 1900's building. It is concrete slab-on-grade, frame construction. I don't know if there is a vapor barrier under the slab. We rent the building.

We want to turn the space into a quilting studio. It has a ceiling mounted heater. Currently, there's old, soiled, "industrial" carpet on the floor that I will replace, probably with similar carpet.

Should I lay a vapor barrier down between the carpet and the slab?

Thanks

beenthere · Dec 3, 2004

I would. Can't hurt, IMO.

Also, I saw a new product at HomeDepot the other day, that is a 2x2 wood pannel with rubber or plastic 'bubbles' on one side. Looks like it would be for covering a concrete floor. Probably too expensive for what you want, but sure looked like it would provide a good subfloor to work from. The edges were tongue and grooved to fit snugly together and not move. Other than that, it looked like it would float.

But in rental situation, maybe the soft pad with vapor barrier that is used under the laminated flooring would be better yet. It wouldn't slide around as much as a layer of plastic under the carpet, I don't think. (Just laid 1100 sq ft of the laminated flooring with that under it).

bczoom · Dec 3, 2004

I believe the practice is not recommended.

When moisture under a concrete slab comes in contact with the bottom of the slab, the moisture can come through the concrete, and, when it comes to the warmer side of the concrete, it will typically vaporize. If the concrete slab is out in the open the vapor will dissipate into the air. You need the concrete to be able to dissipate this moisture. This can also go the other way. If spills occur from the top down, the concrete can help dissipate the spill as opposed to it getting locked in the padding.

In a previous life, I was a flooring salesman (not installer). What we recommended was that a synthetic backing be used in areas where moisture may occur. Use polypropylene or olefin. Do not use jute, cotton, linen, rayon or Kraftcord as they can rot and mildew.

As a side note, I'd recommend getting a good pad as it will help insulate against cold. The floor "area" can get a bit cold in the winter. Without good air circulation near the floor, the cold concrete makes the bottom 6-12" of the room kind of cold. Running ceiling fans or something to circulate the ground air will be a plus.

WVBill · Dec 3, 2004

bczoom,

Thanks, a bit more padding wouldn't hurt - and yes, the room tends to be cold so that will help too.

I just didn't know if I needed a vapor barrier under the carpet/pad and you've answered that.