Hey everyone! Long time lurker, first time poster. First let me thank everyone for all of the accumulated insight over the years.

Second, I've got a problem. Wife and I decided to install a floating plywood subfloor, on to which we'll nail 3/4" oak. We put down ECF underlayment and 23/32 Advantech, cut into 2x8 strips, scored 3/8 on the back and staggered. Slab is level and flat for the most part.

Well...the Advantech is moving when we walk on it! A lot in places. Will the weight of the floor smash it all down? Should I powder attach the ply to the slab, even though it'll puncture the moisture barrier?

We have a crappy bouncy bamboo floor in another room installed by someone else and really wanted to do this right, and.minimize chance of moisture intrusion.

We're so bummed. Any help would be so tremendously appreciated.

Here is a video:

https://youtu.be/G0LDcDP9Xos?si=9lsFtlWtXY1vS0Jg

I don't see any nails

This method of creating a sub-floor is similar to the gymnasium floor that rests on 2X3 treated screeds. The screeds are not fastened down. They sit on neoprene pads.
The screeds are laid out on 12 inch centers and the flooring hold everything in place. With a plywood sub-floor that you have, you will need to use fasteners that do not go through the plywood, maybe inch and a half instead of the 2" that is common for 3/4" T&G. I think that you will have a good job if the slab is flat.

Thanks for the responses. We decided to fasten the Advantech to the slab using 1/4" Tapcon concrete anchors. I used a 3/16 bit to drill through the ply into the concrete, sucked out the hole with a shop vac, then drilled a 5/8 countersink hole (so the Tapcon head is slightly below the plane of the ply).

After running the countersink bit, I sucked out the hole again, filled it with silicone, and drove in the Tapcon. I probably have a 10% break rate or so, but most of that was early on when I wasn't sure what I was doing.

So far everything feels really solid. I had a fair bit of trepidation about drilling through the moisture barrier, but filling the hole with silicone before putting in the screw has assuaged my concerns considerably.

It's slow going. But I think it will be worth it.