I recently purchased the Kentwood 3/4" Prefinished hardwood floor for my office. I'm adding as a underlayment 3/4" T&G OSB on top of concrete.

My question is, is my OSB underlayment thick enough to nair or staple my 3/4" hardwood too? I have read where most installers prefer to use 2" staples...? I'm thinking 2" staples are too long and will not sink enough because they will hit concrete. Am I wrong??? Help.. please

Ya, the 2" may penetrate the moisture barrier, making it useless. I'd use 1½" fasteners.

Are you winging it, or do you actually know what your doing with your large investment in your home??

Wood flooring, especially over concrete, is not just a slap it on the floor, type of job.

You could have some expensive firewood there.

Anyone else would like to reply. Please

Read the instructions that come with your flooring. Nowhere does NOFMA recommend using OSB as underlayment over concrete subfloors. Typically, one uses 3/4" plywood, floated, nailed or glued or a combination of gluing and nailing, along with a vapor retarder. You will need 1.5" staples/cleats if you are installing a 3/4" solid over 3/4" plywood over concrete.

OK now thats interesting Gary, please tell me more why OSB is not recommended on top os concrete. My instructions say OSB is ok to use, but nothing about over concrete. My instructions are very limiting. This partly why Im using this site. Loving it also. What your suggestion? Why not OSB? Should I glue down to the concrete? Thats sounds risky...

Thank you for your replies

Over concrete I would use CDX grade plywood.
I would also use a moisture sealer on the concrete first.

Then either Glue and (nail with concrete flutted nails, or use tapcon masonary screws). The screw are harder to insatal then the nails.
Or lay down 6 mil plastic, then the CDX (again nailed, or tapconed)

Then I would lay the hardwood on top of that (with a moisture barrier under it). I may even use an engeneered hardwood product. Im usually pretty weary of installing solid hardwood directly over concrete, even over plywood over concrete. I have had good sucess with a solid over plywood, but as years go on, and you hear more storys ect, you learn more things.

Using a CDX plywood, is 3/4" thick enough to nail or staple too? or should I go thicker? Also what glue do you recommend? What about using a liquid nail product to make it easier and less messy?

3/4 is plenty thick to nail to (but you have to use 1.5 inch staples and nails) Works like a charm.

subfloor adheasives will do the job for the glue, Tube glue would work (make sure to get one that will adheare to concrete) with that and the nails/or tapcons and the cement sealer you should be set. Oh and a moister test of the concrete is recomended

Publications from NOFMA on subfloors:

http://www.nofma.org/Portals/0/Publicat ... 010_04.pdf
read for installing over concrete starting on page 3

http://www.nofma.org/Portals/0/Publicat ... Floors.pdf
read page 3 & 4

Kind of related...what do you guys think of those 2'x2' squares of T&G raised "subfloor" with the plastic feet for concrete they sell in the box stores?

EDIT: "Floating subfloor" I guess it's called.

http://www.extremehowto.com/xh/article. ... e_id=60385

Thanks Jay and Thanks Gary,

Gary the links were very helpful. I think I better clarify with you guys on the gluing and what I think your both professionally telling me. So if you dont mind I will type out my steps.

1) I'll lay down a heavy vapor retardant on the Slab.

2) Replace the 3/4" OSB I have with at least 3/4" Plywood (Crap another $200.00..lol!)

3) Glue the plywood down and Anchor my subfloor with my powered actuated gun I bought years ago. Nailing in the center and edges ensure no bowing from the board.

4) Layout my prefinished floor in the pattern and random grouping of boards. (Now here's my question, when I finally get to the point of measuring and finding my starting point, CAN I ADD a SMALL BEAD OF GLUE ON EACH HARDWOOD PLANK AND THEN AT THE SAME TIME STAPLE THEM DOWN???? THis is where I would use a calking gun loaded with a liquid nail product?? Just to clarify. AM I close guys? Its not a huge area but it not a small room also. 400sqft.

Thank you again for all your replys.

NOFMA clearly outlines their recommended way of installing a plywood subfloor/underlayment over concrete. I suggest you stick to one of their recommendations. I will say that personally, I do not trust nailed down only plywood on slab connections. I have seen them fail. My preference would be to use a moisture barrier "system" by Bostik's, Franklin, Sika, etc. and their adhesive as well. It is expensive, yes. For 400 sq.ft., you will need approx. 10 gallons of "moisture barrier/sealer" and another 10 gallons of adhesive. Then all that is needed is weight down the plywood panels or spot nail to hold them flat into the adhesive till the adhesive cures, about 24 hours. After that, simply roll out your underlayment paper (15 lb. asphalt felt or Aquabar "B") then install the flooring by nailing only. If you floor boards are over 4" in width, then you may wish to consider gluing the flooring as well as nailing.

Im with gary on this, But I nail the whole sheet down using 20 per sheet of either flutted concrete nails (eaiser for the DIY) or tapcon masonite screws. It is just a little added security to help me sleep at night.

whatever you do, dont lay down plastic and then glue plywood to it (thats only going to glue the plywood to the plastic, not to the floor.

These step we are recommending are not cheap, but they are nessicary to help protect your investment.

To be specifc on the moisture barrier product, which one would you recommend? Can I get it at Lowes and Home Depot? Is some of this product simliar to TAR (Mastic)? I keep reading applying it hot or cold. Am talking the same you have been suggesting?

Let me specify better about the above guys, on the "membrane asphalt system", it sounds like and the reads like I'm sandwhiching the felt between 2 layers of the sticky glue (mastic). Sounds like I would be able to also GLUE the plywood subfloor down to this surface after it drys. Correct?????????? This saystem sounds the safest. You agree?