hardwood flooring underlayment ?

Dreuxgrad

Ed
Senior User
Any suggestions on putting down plywood on slab for 3/4 hardwood flooring install?
In particular the nailing pattern for the ply?
Going over 6 mil plastic with the ply, spaced out from each other and the walls. 15# roofing felt on top of ply.
Any suggestions on sealing ply and or oak flooring- had purchased it sealed all sides from the West Durham Lumber, but not prevelavent here in Texas.
Thanks, Ed
 

waitup

Matt
Corporate Member
I'm a little confused as to what you're trying to do. Are you putting plywood over plastic over a concrete slab?
 

junquecol

Bruce
Senior User
I think you need to put down sleepers (treated) to mount to concrete, and then plywood over top of them. If you are gluing sleepers in place, poly will need to go over top of them. This prevents fasteners for hardwood from hitting the concrete, as they go completely thur the plywood. Once the sleepers are DRY, you could glue them in place. I would use SS screws to fasten ply to treated
 

waitup

Matt
Corporate Member
I think you need to put down sleepers (treated) to mount to concrete, and then plywood over top of them. If you are gluing sleepers in place, poly will need to go over top of them. This prevents fasteners for hardwood from hitting the concrete, as they go completely thur the plywood. Once the sleepers are DRY, you could glue them in place. I would use SS screws to fasten ply to treated
Or poly under the sleepers and let them float with plywood and flooring. Seal the seams of the poly and all of the wood will stay dry.
 

KenOfCary

Ken
Staff member
Corporate Member
I used a product called DriCore R+ which has a foam underlayment and OSB on top. Sold in 2'x2' squares that lock with T&G. Special order from Home Depot for a little less than $2/sqft. (price may have gone up like everything else) It's a floating sub-floor - you can add a finished floor on top of it or just paint it gray like I did. It also has channels on the bottom of the foam to allow water to flow under it if the concrete floor sweats. There are probably pictures in my gallery. Heavy equipment rolls over it very easily.

Adds some insulation and cushioning for the knees / ankles on concrete.

I used a similar product in my first shop called OVRX, but it doesn't seem to be available anymore in the US.
 

Oka

Casey
Corporate Member
Seal the concrete with Eculid or equal. Then install the sub floor system then the subfloor.
Moisture sealing the concrete is the best approach... unless the ground doesn't ever get wet.
 

jlwest

Jeff
Corporate Member
I installed laminated Shaw Hickory flooring directly over the cement slab with Shaw glue. This a approved manufactures procedure. I am not sure a slab 8 inches above grade gets wet. Usually a plastic barrier is put down before the slab is poured per code. Never had a problem in 10 years.
 
Last edited:

charlessenf

(;harles
Senior User
Wow, so many different suggestions/approaches. When i did my shop, I laid plastic down, then gravel and reinforcing mesh and then applied a concrete sealer. Lots of moisture in our 'soil' here. Ice crystals form on the surface in the winter - appear to grow up out of the dirt! But shop floor is dry.

Built in the Sixties by NTWGB*, I don't think they laid down any moisture barrier under the basement slab of our house and know they did not seal it. Nor, I suspect, did they do a particularly good job sealing the exterior block foundation - we get moisture down there.

So, in my case, I'd want to isolate any organic material(s) from the weeping slab (not that I'd think of putting a hardwood floor down there!

I spilled some of the sealer on the basement floor (I think the metal 5G can leaked) and that dried up and appears to have sealed the concrete nicely. If I ever can empty the space, i might pour five gallons of that sealer over the slab and see what happens.

There are MOISTURE TEST KITS one can get to see if the concrete slab is dry or not. They are cheap - so try that first as it is much easier to do before laying the hardwood flooring.


* Not the world's greatest builders of Lenoir LLC
 

Dreuxgrad

Ed
Senior User
I think you need to put down sleepers (treated) to mount to concrete, and then plywood over top of them. If you are gluing sleepers in place, poly will need to go over top of them. This prevents fasteners for hardwood from hitting the concrete, as they go completely thur the plywood. Once the sleepers are DRY, you could glue them in place. I would use SS screws to fasten ply to treated
Morning Bruce- I'm matching elevation of adjacent room. Did the sleepers, and culled foam from Habitat, for the shop in Durham. Worked great-had no problems, but haven't heard from new owners(compliments or complaints)
 

Dreuxgrad

Ed
Senior User
Wow, so many different suggestions/approaches. When i did my shop, I laid plastic down, then gravel and reinforcing mesh and then applied a concrete sealer. Lots of moisture in our 'soil' here. Ice crystals form on the surface in the winter - appear to grow up out of the dirt! But shop floor is dry.

Built in the Sixties by NTWGB*, I don't think they laid down any moisture barrier under the basement slab of our house and know they did not seal it. Nor, I suspect, did they do a particularly good job sealing the exterior block foundation - we get moisture down there.

So, in my case, I'd want to isolate any organic material(s) from the weeping slab (not that I'd think of putting a hardwood floor down there!

I spilled some of the sealer on the basement floor (I think the metal 5G can leaked) and that dried up and appears to have sealed the concrete nicely. If I ever can empty the space, i might pour five gallons of that sealer over the slab and see what happens.

There are MOISTURE TEST KITS one can get to see if the concrete slab is dry or not. They are cheap - so try that first as it is much easier to do before laying the hardwood flooring.


* Not the world's greatest builders of Lenoir LLC
Spec built in '98, Texas cracking slab. Just bought a meter for a different issue. Had that can problem in Durham-Woodcraft replaced it. Thanks
 

Dreuxgrad

Ed
Senior User
I installed laminated Shaw Hickory flooring directly over the cement slab with Shaw glue. This a approved manufactures procedure. I am not sure a slab 8 inches above grade gets wet. Usually a plastic barrier is put down before the slab is poured per code. Never had a problem in 10 years.
Perhaps, elevation is important. Another local professional suggestion was for gluing-so must be popular here.
Thanks
 

Dreuxgrad

Ed
Senior User
Seal the concrete with Eculid or equal. Then install the sub floor system then the subfloor.
Moisture sealing the concrete is the best approach... unless the ground doesn't ever get wet.
Alternates here in north TX, had months of no precip, and now at least once a week. Six mil poly was the local suggestion. Taped and sealed(but with nails through it) so don't know effectiveness. We are on a slight rise so just in case the 1k flood happens....
Thanks
 

Dreuxgrad

Ed
Senior User
I used a product called DriCore R+ which has a foam underlayment and OSB on top. Sold in 2'x2' squares that lock with T&G. Special order from Home Depot for a little less than $2/sqft. (price may have gone up like everything else) It's a floating sub-floor - you can add a finished floor on top of it or just paint it gray like I did. It also has channels on the bottom of the foam to allow water to flow under it if the concrete floor sweats. There are probably pictures in my gallery. Heavy equipment rolls over it very easily.

Adds some insulation and cushioning for the knees / ankles on concrete.

I used a similar product in my first shop called OVRX, but it doesn't seem to be available anymore in the US.
thanks Ken- elevation matching is most important the older we get, so going with existing combo
 

Dreuxgrad

Ed
Senior User
Or poly under the sleepers and let them float with plywood and flooring. Seal the seams of the poly and all of the wood will stay dry.
Did that very suggestion on the Durham shop-and put scrap 1.5" foam between them. Worked great even with my equipment. Although I don't have a Tannenwitz or 20 inch jointer ;(
 

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