No industry approved method of doing this without first removing the existing parquet floor. After the parquet is gone you have numerous options on both material and installation methods.

You should never make a sandwich out of wood installed over concrete.

If you lay stone, donÂt install it over plywood in any case, concrete is the best base for stone.

In regard to the hardwood floors, some require Nail, Staple, Float or Glue down.
When it comes to nail or staple you will need to have sub floor in most cases.

I know you can install solid bamboo with glue directly on concrete with moister barrier,
If all solid are requiring nail or staples, I donÂt think so, but I am not sure maybe some else will help with that question.

Jerry, are you saying then that solid wood plank if glued down CAN be glued to concrete with the barrier? How can it be glued to the concrete though and still have the barrier?

If a wood sandwich isn't good, why do they want to install plywood under the planking? It seems there is already a solid subfloor there with the existing parquet. I'm really confused.

When you have a concrete slab with a wood floor glued down over it... you can't cover that existing wood floor with another wood floor nor a plywood subfloor. No manufacturer will approve that type of installation. The parquet is supposed to be removed first down to the bare concrete. Then you can either tile or go back with another wood floor.

If your friend had parquet glued over a plywood subfloor and standard floor joist.. no problem there. The concrete slab is the deal breaker.

You can glue down a solid wood floor directly onto the concrete following NOFMA guidelines, but I never recommend that method to people. Too risky imo. I feel folks are much better served to choose an engineered wood if gluing down.

When you say "barrier" you must mean a poly or plastic moisture barrier. That is what is used if the floor floats.

Underneath glue-down floors the "barrier" is a rolled on or troweled on membrane/sealer. You don't always need this but it very cheap insurance underneath a wood floor.

Do a google for Mapei WFM, or... Bostik's MVP Those are urethane, troweled on, moisture membranes, used with those companies adhesives.

Jerry, thanks again for your response and to all who responded. She had intended to take the parquet up first. What I'm still not understanding though is why the plywood subfloor is better. What properties would that have that the existing parquet floor doesn't when used under the new wood? If the tile doesn't require a subfloor, putting down stone or porcelain tile over the concrete might be a more cost effective solution for her.

I can get dangerous so bear with me on this... also Floorguy knows more about slab installs than i do.

The parquet you friend has is a 3/4" solid wood glued directly to concrete that emits moisture vapors... all slabs do this. Solid woods are very susceptible to moisture changes and you have a high probability of the Parquet getting sandwiched and wanting to move. The only way for it to move is up, and that is not good.

Plywood, on the other hand, is a laminated product in sheets using exterior glue and is not as susceptible to moisture changes as a 3/4" solid piece of wood. Plywood is made the same as engineered wood .. in crossing layers.

There are several ways to install a plywood subfloor over a slab and the installer would need to follow both the wood manufacturer and adhesive manufacturer's guidelines for doing this. NOFMA has quidelines that can be printed out.

Plywood/engineered wood, is more dimensionally stable then it's solid counterpart. Solid wood sandwiched over concrete, is making a small greenhouse, not to mention dew points from the colder concrete. That solid wood parquet is going to gain moisture content and swell. It possibly could buckle under the new floor.

It is required, not just recommended, that the existing parquet, be removed, and the slab prepared to requirements for the new flooring.

Never glue a solid wide plank, to concrete. I would be scared to do the subfloor over concrete, unless I thoroughly investigated the concretes moisture and the signs of the ability to gain moisture.(grading, down spouts, drainage, etc.)

Thanks Jerry and Floorguy. Now I understand why the plywood is better. I think though the original solid wood parquet was glued down to the concrete without a subfloor, and that has survived almost 50 years with none of the problems you mentioned. Maybe the 5 "slats" in each parquet module act as expansion joints and allow for any swelling, or movement, and stop the floor from buckling. Thanks again!

In a parquet, the swelling is not all in the same direction, at once. The grain is going in all different directions, depending on the pattern. They are also Shorts"