Hand hammer the powder driven nail and see if it splits the concrete. It must be hammered at least 1″ into the concrete. Go to the web site of this rather specialized trade before you start at www.patmi.org. I see far too many poorly installed subfloors on concrete, avoid this with a little knowledge from the powder activated manufacturers association. You can also try Tapcon screws, but I have not had much good luck with these. And the concrete anchor sleeves are a rather slow and clumsy method for this operation. Find a method you are most confident and comfortable with. As an added measure of security you can add glue (try the new urethane construction adhesives, with their tremendous holding power) to the plywood. Scoring the plywood (with 1/8″ deep circular saw kerfs) helps it lay down flatter. You can also try installing 1/2 sheets of 4’ by 4’ plywood. But really, your concrete slab will need to be flat like I described earlier, or you will have no end of frustration with this method. It all sounds like a bit much doesn’t it? But if you don’t take the time now to get the plywood down firmly, you’ll regret it later.
The last and the most experimental method of installing a solid wood strip floor to your concrete subfloor, is to glue hardwood shorts directly to it. These have to be specially milled for this purpose. They will need to be no more than 2 feet long, and have a flat underside. And they should not be more than 1/2″ thick and 2″ wide. If you look at the standard strip floor you will notice it has a grooved bottom which will not contact the glue as well as the flat milled bottom. This will become apparent as you start installing with this rather clumsy and slow method. In this case, use a good urethane adhesive, nothing less will do, and Dri Tac 7500 is one of the best. But even Dri Tac’s technicians admit this solid wood glue down application is terribly difficult, and should be left up to the professional. But for you die even harder D.I.Y.’ers I have a few hints. Don’t spread more glue than you can install floor on, in a half-hour. These may be the most precious few rows indeed, when you see how these solid wood shorts move out of place, as soon as you look away. Use a 3M releasable tape product to keep them in place, or use the ratchet straps that the Pergo floor installers use. Let the first few rows set up for an hour or two, so the whole start of the job doesn’t shift.
The trouble with this last method is that if the finished floor encounters excess moisture or simply gets a little wet from a spill, the floor will buckle off the glue. Unlike parquet (with expansion in all directions) strip floor directly on the concrete is really susceptible to even minor water damage. The floor is basically trapped in it’s own glue, and the stress of even minor expansion just wrecks this type of floor installation.
So there you have it all the good and not so good methods of installing wood floor on concrete. If it were me I would choose an elegant parquet pattern (saxony is my fav.) and glue it directly to the slab. Of course I would pick the unfinished square edged parquet so that I could sand it silky smooth, apply dark walnut colored stain, and finish it with at least 3 coats of satin polyurethane. This makes for an elegant, simple and durable floor, and puts those clumsy multi-layer nail down operations to shame. But make up your own mind, I hope I’ve a least opened your mind to the various possibilities.