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I have bare concrete floor that was, until recently, covered with carpet. After recently seeing a friend of mine purchase raw pine, shape the tongue-and-groove himself, and seal it to achieve a wonderful result, I wanted to do the same. The difference is that he was nailing directly to an existing wood floor, and I'm going over a concrete slab on grade.

I'm leaning toward a floating installation because I'm doing it myself, so it's less cost and less effort. Almost everything I've seen is suggesting that the strata should look like so (From bottom to top):

  1. concrete slab
  2. moisture barrier
  3. 3/4" plywood (fastened to concrete)
  4. moisture barrier
  5. hardwood nailed to plywood

However, I'm thinking that I'm going to run into issues with door clearances using this approach. Can I use thinner plywood in layer 2? Or my alternative thinking:

  1. concrete slab
  2. moisture barrier
  3. hardwood glued at t&g joints

Does this approach make sense? What are the potential issues? Does gluing the joints help or hurt?

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Door clearance can almost always be solved by trimming the bottom off the door. – Michael Karas Jan 15 '13 at 1:43
gluing every joint seems like a whole lot more work than attaching to a floating subfloor. – DA01 Jan 15 '13 at 22:14
I just noticed these are 1x12s that's going to potentially exasperate your expansion/shrinkage. You may want to acclimate these boards for a year or so in the house before permanently attaching them (either to the subfloor or to each other). – DA01 Jan 15 '13 at 23:19
@DA01 wow.. a whole year? I thought 3-4 weeks would be appropriate. I'm in Las Vegas, where relative humidity in my house is around 12-14%, outside is not much higher – snicker Jan 16 '13 at 4:20
hard to say I guess without knowing where the wood is coming from. If it's kiln dried from a lumber yard you might be good to go. But if it's Home Depot and the like, it's possibly fairly wet wood still. – DA01 Jan 16 '13 at 4:26

You can float wood flooring installs over concrete. Moisture is your primary enemy here, and uneven concrete will also be evident in the finished result.

I would consider painting on a moisture barrier, and then using a moisture/sound/mold/mildew/pad atop that.

You should absolutely glue the joints. Set the first three courses straight and true and let the glue dry overnight. Afterwards, glue each joint and use blue painter's tape every few courses to hold them together.

An uneven floor will show up more if your wood isn't beveled, and you'll notice dips with "springiness" in the finished wood floor.

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The door heights don't matter, you can cut the bottoms to fit your flooring. However you do need to be close to the flooring level in whatever room(s) you are attached to.

This wood may need to sit a while too and you may need to buy a moisture meter. Not knowing where you are getting it from or the exact grade it is hard to give advice on this. 3 weeks would be my minimum.

And then lastly float vs nail... I don't think it is a choice. Good floating floors require very tight, precise, and most of the time curved cut-outs. I am not sure you will have the skills or equipment to do this. Companies that produce floating flooring go through these issues (sometimes with poor outcomes) so I would highly recommend not going this way. Also if your connections are a little loose you might be happy after the install but have issues a year or two down the road.

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I am a big fan of DriCore. These are interlocking tiles, about 2ft on a side that combine a moisture barrier and a particle board surface as a subfloor.


The barrier is a waffled plastic that actually lets any free moisture be exposed to air to dry out. It is a bit thicker than 3/4 but adds more opportunity to solve any residual mositer problem.

I would also pre treat the floor with a Drylock type waterproof paint before installing the DriCore.

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it's a nice product but might be overkill for above grade (since it's typically used for moisture-heavy areas...if the above grade slab is whicking up a lot of moisture, there are perhaps bigger problems that need solving first.) – DA01 Jan 15 '13 at 22:16
How can it be a moisture barrier if it allows moisture to be exposed to air? – ArgentoSapiens Jan 16 '13 at 0:24
The waffle lifts it over the concrete and the sides are open allowing some air to circulate under the subfloor. A gap is left around the edges. – bib Jan 16 '13 at 22:39
@ArgentoSapiens: it's a moisture barrier because it doesn't let moisture underneath the DriCore tile permeate up into the plywood layer and the flooring above. It isn't a waterproofer (like Drylok paint). – Shimon Rura Jan 17 '13 at 3:06

Most floating flooring systems have a plastic bubble wrap/like plastic barrier between the original floor (be it concrete or wood) and the actual floor material (usually a laminate).

I was thinking a paint on moisture barrier. But seeing as the laminate flooring barrier is plastic it would protect the wood from rising damp anyway. It probably wouldn't hurt to do both.

Laminate flooring is quite thin compared to real wood so you may need to plane the bottom of your doors to fit.

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