Hey all!

I can't seem to get a straight answer about laying solid hardwood flooring over concrete that is above grade (2nd Story). Being my first time laying hardwood flooring, I'm a little nervous about laying the Solid Brazilian Cherry (3" x 3/8") over the Concrete, or Gypcrete floor. The flooring is going in the closets and in the foyer [~100 sqft]. My two concerns are moisture, and securing the floor down.

I've already laid a 1/2" ply base via nails to the concrete, without a moisture barrier. Whoops? Since I'm above grade do I still need a moisture barrier? It was a real pain securing the ply, and I would like to avoid having to take up the sub floor but also don't want to have the floor start to buckle.

My moisture concern is getting me worried about how I secure the flooring. I assume, correct me if I'mm wrong, that if I use a glue, and the floor buckles, there is little chance of repairing it. So I am leaning toward nailing it down. Is this a good choice? If so what is better cleats or staples and what lengths, respectively, should I get?

Now thats a great question, how to fasten an underlayment on gypcrete. Gypcrete/concrete in pans...gypcrete on a wood substrate can all have moisture issues. You'd think exactly the opposite since it is above grade. But in fact even those floors and concrete twenty stories up can have moisture issues.

The worst scenerio is to have gypcrete poured over concrete on grade. Lucky for you.

Best thing to do is to isolate the wood from the gypcrete, even the underlayment. If you fasten the underlayment through the gypcrete to the (if there is wood under it and not a metal pan) your going to fracture the gypcrete. I've seen that stuff turn to dust as well as spiderweb'd chunks. Fasteners won't hold in that scenerio for ever.

So I would first use the Ardex gypcrete topping and then use a trowel on vapor retarder like Bostik MVP4 then glue the ply on top of that and then fasten the wood to the ply. But not into the gypcrete.

Or take the wood back and get an engineered you can float over it with an appropiate underlayment.

But thats just my opinion.

Floormeintucson,

Thanks for the reply. After doing some more research, it appears that Gypcrete was not really used in construction prior to the early 1980s. The condo building that I reside in was built in the early 1960s. Now, I did have to use a Powder Actuator gun to secure nails into floor. There was no distinct failure trademarks of Gypcrete as you describe. I have also done some electrical work in the ceiling which has allowed me to view the bottom of the floor above me. It isn't wood, it appears to be metal with some sort of covering.

Without it being Gypcrete, how does this change your recommendations?

I now know that I should have gone with engineered over solid. My mistake, however, I have already opened two of the three boxes. No returns possible.

Back to nailing it down, do you have any recommendations of nails or staples? What about fastener length for 3/8th over 1/2 ply?

Alright, so I just had a local flooring company swing by my place to see if they said. They were familiar with my building , and said that I could "float" the floor since it was such as small area by gluing the boards together (on the tongue and groove). They did not recommend using nails, or staples on 1/2 ply with a felt insulayment as it would just pop up. The company is very reputable and has a stellar review base on google. They offered to do the work, but said I could just do it as easily myself.

Has anyone ever heard of gluing together 3/8" solid hardwood flooring and floating it?

The area is just a small foyer, two small bi-fold door closets and a walkin closet...

So...is it concrete or gypcrete? Any time you fasten down wood directly to a "crete" substrate your looking for trouble.

I don't recommend floating solid, I doubt any one here does either. If that stellar company said to glue the T&G I'd let them do it so they can do it over when it fails.

Ditto that. IMO floating solid, even 3/8, is asking for problems. By the way...Who's the manufacturer? Are they o.k. with floating their solid?