I am installing 3/4 hardwood on top of my concrete slab but I will be screwing down plywood first. What is a good quality underlayment for this type of application?

I am going to use Tapcon concrete screws, would it be worth applying concrete silicone to the hole in the concrete after drilling then applying the tapcon?

 

Plywood directly on concrete is not a good idea, even with a vapor barrier. What good will the barrier be with 10 kazillion holes in it? How do you propose to drive 2" staples or cleats into your hardwood and plywood without it going all the way into the concrete? Never heard of concrete silicone, but applying it to the holes may not do what you think it will.

 

I agree 100%.
A floating engineered can be installed over a slab with a vapor barrier under it.
Any wood subflooring laid over a slab is going to rot out.
Engineered flooring is prefinished and is far more stable then any 3/4" real wood flooring and is not going to need sanding, staining, finishing.

 

Going to add a 3rd nod to not laying plywood (or any wood not pressure treated) on concrete. Engineered flooring comes in both click lock and glue together, either one would work nicely in your situation. This type of flooring comes in various thicknesses from 3/8" to 3/4".

 

I should add that there is currently carpet in the room now, I pulled up the carpet and found asbestos vinyl tile. The floor is completely level and I was just going to go over it with the plywood. I do not want to to a floating floor because I have the feel/sound of it.

I was going to go in with 1 1/2" staples. The go in on an angle so it should be sufficient. As for the silicone, this should work...

DAP Products - Silicone Sealants - DAP® Silicone Plusâ„¢ Premium Silicone Rubber Concrete & Masonry Sealant


I am going with Pressure treated plywood

 

You are set to do this and want blessings. You won't get them here. Good luck with the project.

 

Pressure treated ply inside is not a great idea....

To what experience do you have with floating floors? What can you tell me about "feel/sound " that is off putting? I have quite a few satisfied customers with floating floors. The only time you may have issue is if you drop something, it can have a hollowish sound. Other than that, you would be hard pressed to believe that it is not nail down and is a floating floor. So, if you are constantly dropping things, then this may not be for you. But to Larry's point, you seem pretty steadfast on doing things your way, so enjoy the experience.

 

Good luck. The plywood over concrete will work short term, but will rot out in a few years. I would never use pressure treated wood indoors. Too many chemicals. And treated wood will rot, it just takes longer.

 

With pressure treated plywood the staples will rust out in a few months because it's treated with copper.
Ever taken the time to look at pressure treated plywood in the store?
It's full of voids, often delaminating and soaking wet.