Hi Everyone...
First off, great site with tons of useful info--thanks.
Reading through some previous posts it would seem that most folks glue &/or nail their plywood subfloor down to the slab rather than "float" it.

What would be the professional opinion of a floating plywood subfloor over a slab?

My Plan...
I was planning on leveling the slab first, then testing for moisture/vapor emissions. A moisture/vapor barrier would then be installed on the slab before plywood is layed.
The plywood subfloor would be two layers of 1/2--overlapped and running in opposite directions. The top 1/2 would be glued (liquid nails?) and screwed to the bottom 1/2 (screwed every sq ft or more).
Flooring will be stapled (BR111 Triangulo) on the plywood.
Looks like I'm ending up with ~1 1/2 of total wood thickness--clearances are not an issue in this install btw.
Seems pretty solid to me, but I'm certainly no pro..just a DIYer

Thanks Everyone...Merry Christmas

We had a poster about a year ago that did his entire house (or most of it) exactly this way. According to him, it turned out quite well. We all contributed ideas and hints, as well as cautions and advice. You could search this for the thread if you need to.

davhut1,

What you are talking about is the standard floating sub-floor install. Most here would say that it is the best thing going for wood on slab. For the most part it is overkill but when it comes to moisture, overkill is not a bad thing, once the floor has been laid you cannot go back and repair it without loosing your investment so you only get one shot at the sub-floor. The only thing that I would suggest is to add a layer of 15 weight felt paper over the top of it. It helps to soften the step and deadens some noise.

I love doing floating subfloors.

I've even done them with rubber cleats under the subfloor. Now that is overkill!!!

Thanks Guys.
Sounds like I'm heading down the right path.
I will install the felt paper between the flooring and plywood.
Not sure about the "rubber cleats" though???
I want it to be nice and solid with no problems down the road.

I really appreciate the pointers. I'll see if I can find that other post on the floating subfloor.

Thanks Again!!

Regarding the floating floor technique being discussed here, once he nails down the floor to the floating sub floor, what kind of expansion and contraction can one expect as opposed to securing the sub floor into the slab with screws or nails?

Best...Stan

The exact same. Expansion doesn't matter how it is laid. It is going to swell when it gains moisture content and it is going to shrink, when it loses moisture content.

Hello-

I have been reading through many posts on this board for the past couple of weeks in preparation for my ¾” Brazilian Cherry installation over concrete. I have installed 3/4” hardwood once before, but never over concrete with plywood sub floor. I will be preparing a floating sub floor with 2 overlapping sheets ½” cdx plywood.

I want to use the same method VP used in this thread:
http://www.hardwoodinstaller.com/hardwo ... ab&start=0

I have a couple of questions:

1) I found sheets of ½” 4x8’ 3ply CDX Plywood on sale at Home Depot for $10.99/sheet. Do I need to have these cut to 2x8’? If so, why?
2) Should there be a 1/8” of space for the seams between each sheet of 2x8’ plywood? If I can leave the sheets at 4x8’, do I need to place more than a 1/8” gaps at the seams? 1/8” gaps in the middle of the floor are alright to install over? I know to overlap the boards so the moisture barrier/concrete is not exposed.
3) I plan on gluing, then screwing the 2 sheets together. What type of glue and screws should I use to secure the two sheets of plywood together? How much glue should be used?


Thank you everyone has contributed to this board. This place is the most valuable hardwood floor resource available on the net.

-Luke