Hi Anand,

What did you end up doing for your subfloor? How did the installation go?


Gary--once the hardwood floors are down, can you tell a difference between the different subfloor attachment methods used by walking on them?
Is there any downside to a floating subfloor installation on an at grade slab?

Hi Wolfgang,

I did not attach the plywood to the concrete. Just laid out (on top of #15 tar + poly + insulayment), then another layer of #15 tar, the nailed the hardwood. I've gotten about 30% done, and it seems very good so far. It feels more solid than the upstairs (over wood subfloor). But it isn't as "hard" as glue-down, so just the right amount of give. There is one place at the end of a run where I topnailed the last row of the hardwood. The previous row is not nailed (no space to nail). Here the floor moves more than I would have liked, makes a sticky sound, probably the loose hardwood touching the tar paper and coming off when I step off. I might just topnail the previous row or something, probably should have put some urethane and stuck that row to the ply.

I used 1-3/4" nails, coz I had the luxury of about 3/16" insulayment underneath the ply. I can feel the nails really catch, probably right to the bottom of the ply. This insulayment really insulates the place. I've actually claimed the insulayment as tax credit.

I got delayed a bit due to other stuff happening (this is my hobby project), but things are moving again now.

Hope it helps.

i too have similar situation with plywood to concrete . was wondering how the floating floor worked out . have read hundreds of post here and elsewhere , but few come back and discuss their results when done .

thanks

Thank you for posting. Usually I dont post to threads over 1 month , ( Administrative rule ), but yes....It sure would be nice to hear from people after their projects, I often wonder how it went.

It worked out well actually. Even the one place with the sticky sound described above somehow settled down and is fine. The floor feels solid, does not feel like a floating floor. The insulayment under the plywood is great, it does not feel cold at all, even the carpet was colder.

But I have to tell you it was hard work doing this with the house occupied. Example I had to move stacks (about 3 tons) of wood around again and again because of the two layers. And you need to do quite a bit of redos of thresholds, hearth etc. due to the height increase. If I could go back, I would have selected engineered hardwood and glued it down on the concrete.

i was thinking of 2 layers of 3/8 cdx crossing overlapping patterns and screwing them only together for 90 % of the floor . but adding tapcons at threshold areas in front doors and cabinets . i like the idea of not putting screws or powder loads thru the moisture barrier , here in south florida the slab is only feet away from water . my concern is the slight unevenness of the concrete floor causing loosening of the staples ( 2 " into 3/4 oak ) because of some flex in the plywood floor . anyone try this approach in the south ? was hoping to get the project started over the holidays ( house is empty ,no furniture ect ) but cant seem to decide what the best practice is as the more i read the more the floor prep stories change . any input wood be great ( pun intended ) ./

I'd go with the two layer floating subfloor. But stapled together, staple while standing overtop. Then theres the newer screw guns that you can use standing up, works pretty fast and holds better of course.

i assumed i would screw the two layers together , any reason why i should worry about a floated subfloor like this in south florida ? can anyone see a problem with this and 3/4 oak staple down .?

I'm all for floating the plywood. But why 2 sheets of 3/8" screwed together? Why not float 1 layer of 3/4" CDX, using the method described earlier?

"I'm all for floating the plywood. But why 2 sheets of 3/8" screwed together? Why not float 1 layer of 3/4" CDX, using the method described earlier? "

3/4 boards may have raised ridges at end joints , so if the oak is nailed to the first that is slightly raised the second staple in the slight lower one would be under lift
pressure when nailed . my idea was to have a subfloor that acts as a whole sheet . i am not a a flooring expert by any means , but as a general carpentry approach the layers seem to yield more cohesion and less rift between boards . is there a issue with layers that will arise when i go to staple down the oak ? thanks .

Haven't had any issues with plywood edge rise, using flat/dry 3/4 CDX, cutting the sheets into 16"x8' panels, relief cutting, and staggering joints. Along with fastening 3/4" hardwood...it's a very stout and flat installation.

Really the only issue I see to be aware of with your process....when staggering and fastening the 2 layers...I believe this sandwich may be suseptable to binding when secured together. Typically when fastening a sheet, your working from the middle of the sheet to the edges, where as staggering 2 sheets and fastening them together, I see this as impossible due to the stagger, and possibly creating pressure within the fastened sheets.

Using two layers of 3/8th vs one sheet of 3/4 makes for a more stable installation. Just run the top sheet 90 dgress to the other, dont have to 45 anything.

Stability in what respect ? I guess I don't see or have not run into any stability issue with the NWFA floating spec on one layer of 3/4". Just seems unecessary floating and securing 2 layers of 3/8". I'm all for overkill and perfection, but........Hey knockith thow lights out

why 2 layers 3/8 vs 1 layer of 3/4 ply ?
i actually laid out both and felt the 2 layer approach compensated for floor variance better than the single layer of 3/4 . cost different is about 150 bucks for the whole area . but the time and labor is much greater , accept with two layers of 3/8 i dont see a need to kerf cut the backs like you would a 3/4 plywood float . unless i am mistaken ? i figure a little gorilla glue between sheets would help hold staples/screws , but the question i have now is what stapler and staples ? and are there any 5/8 screws that will self counter a bit on there own, like durock ones will ? or should i scratch the screw idea because of the increased chance of hitting one with a 2 inch floor staple will laying the oak ?

any insights from the "experienced" would be appreciated .

Howard, the way I look at it is like this....do you feel better nailing a haredwood floor down over two layers of plywood or just one? I know I know they equal the same thickness but think about it.

I use my Senco SNS41 with 7/16 crown-5/8 staples shot in at a sort of 45 degree angle while standing on it so they are counter sunk.

Some day maybe Ken and I can do a video about it.