# Help Installing Hardwood over old/new Concrete Slab



## Hages (Sep 2, 2006)

Hi,
I am building a 2-story home for the first time and the first floor is a mix of
old
and new concrete slab thanks to the expansion of the original floorplan.
Basically I
tore it down to slab, added the new areas and reinforcement footings.

So I spoke to one flooring guy about how he would approach the hardwood floor
install:

1. 2 sheets of 3/8" plywood 
2. Vapor barrier paper
3. Oak Hardwood
4. Finished floor from slab is 1.5"

He said maybe some concrete leveling. I wasn't so convinced he knew what he was
doing. Sounds reasonable?

I was thinking that at least to check the slab straightness was to:

1. 6 foot level to find high-low spots
2. Correct with a concrete leveling such as Ardex K-15

How would you check and prep for hardwood over slab and what underlayments would
you
use? I live in the San Francisco area so we don't get frost or any extreme
climate
temps.

Thanks for your help!


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## georgia dawg (Aug 12, 2005)

I try to talk my customers out of solid hardwood flooring below grade. You might try engineered wood. You can then still call it a "wood floor" and you honestly can't see the difference. If you go solid wood however, I've had good luck with this method:

a. level floor
1. seal concrete
2. lay down 6 mil poly vapor barrier. overlap and tape joints.
3. fur out floor 12" o.c. with pressure treated 1x material, around 
perimeter, too. be sure concrete nails are slightly countersunk
for shrinkage of the p.t. wood.
4. add 1 layer typical wood subflooring (3/4" advantech, etc.)
be sure nails aren't too long to hit the concrete or angle them.
5. nail down floor as you would on a regular wood sub-floor, considering
the furring strips as your "joists"


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## Teetorbilt (Feb 12, 2004)

You definitely don't want wood between the slab and vapor barrier.


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## Hages (Sep 2, 2006)

Teetorbilt said:


> You definitely don't want wood between the slab and vapor barrier.



Teetorbilt,

Question on why not a vapor barrier between the concrete and the wood? Where else could it go between the subfloor ply and the concrete surface?

I like the idea of sealing the concrete as an added measure, but furring for the subfloor?? 1.5" from concrete to finished wood surface seems plenty high already and adding a furring layer would be a bit much, I would imagine.

BTW, this is not below grade. And landscape will be properly graded to keep the drainage away from the foundation as much as is possible.

Thanks for your opinions!


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## georgia dawg (Aug 12, 2005)

Be sure you have at least 3/4" something or another underneath your 3/4" solid wood or your 2" nails, even at an angle, are going to hit the concrete. Using shorter 1 3/4" nails instead of 2" can help alleviate this issue some. I wouldn't go any shorter, though.


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## seanmsimon (Jun 4, 2008)

*Why not 3/4 ply sleepers*

I am about to start a remodeling project in south Texas. Many of the older homes in this area that have solid wood over concrete slabs have solid 3/4 sleepers set in tar. I am considering hardwoods for this new project. 

Does anyone have feedback on setting 4" strips of treated 3/4 plywood in rivers of tar for the sleepers? I am trying to minimize the height but do not want to use engineered.


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## Floordude (Aug 30, 2007)

Screeds in an asphalt bed, work well, as long as the moisture emissions are not sky high.

Not only will the screeds need to be set into ashalt, the entire floor needs to be covered as a complete membrane. Then a minimum of 2 coats over the screeds. Pretty messy, if you ask me.

Pressure treated wood, is going to have a high moisture content. Be very careful, as it can cause cupping.


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## genecarp (Mar 16, 2008)

georgia dawg said:


> I try to talk my customers out of solid hardwood flooring below grade. You might try engineered wood. You can then still call it a "wood floor" and you honestly can't see the difference. If you go solid wood however, I've had good luck with this method:
> 
> a. level floor
> 1. seal concrete
> ...


this will work well, i have used this approach as well, you can even add 3/4'' rigid foam between the 12'' centers, adds a little insulation.:thumbsup:


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