Solid Hardwood, Engineered and Laminate Flooring - HUGE prep-concrete-for hardwood mistake-help!

I have a 11.5' x 9' area of smooth concrete, onto which I want 3/8" pre-finished flooring installed. The area used to be an outside patio, which the previous owners enclosed. Since they cut every corner imaginable, I am not confident that the concrete was poured with the proper plastic sheeting at its foundation. I did extensive research: bottom line, I needed a vapor barrier and then plywood on top of it, onto which the floor would go. I went to Home Depot to buy mastic and 15lb felt roofing paper. Pro there said to use Henry's 107 Asphalt emulsion (roofing stuff), as it would be easier and contractors had been recommending it. So I spent Sunday putting a coat down and laying the paper on it, and felt pretty darn good about it.

Floor installer just came, said I had tear up the paper, and then I have two choices: sand and reseal the concrete, or put mastic down (will act as a vapor barrier), then plywood, then mastic again, then the flooring. The mastic option will cost me $700, with installation on top of that.

I have wept, and now I am dusting myself off and see what I can do to fix it, or if I just have to accept it and move on. If anyone has any suggestions or words of wisdom, I'm ready to hear them! Thanks.

Well you may or may not have needed a moisture retarder. Did you test the concrete for moisture vapor emissions?

There are moisture blocker and adhesives systems on the market to block vapor emissions, so you can glue engineered directly to the concrete.

Plywood over concrete is only for nail/staple down solid wood flooring.

Since you had planned on the plywood and you have the start of the proper moisture retarder, I say continue with what your doing. on top of the asphalt impregnated felt, lay out poly plastic and then install a floating plywood subfloor. Much better then anchoring down the plywood and puncturing the moisture retarder(what is the purpose of the moisture retarder if your going to put holes all in it?)

Cut the 4x8 sheets into 2x8 sheets and stagger them across the floor, the opposite direction your going to lay the flooring. Use a piece of the plywood as an expansion guage. Be sure to acclimate the plywood and check it with a moisture meter, just as you would with the finished flooring, before you ever install it.

I'd ask my installer, to see his moisture meter. If he cannot produce one on the spot, you may not be dealing with a true professional.