# Plywood over concrete slab



## JesseCocozza (Aug 20, 2011)

Working on a house where nail down wood flooring has been chosen. In the past I've ran 30# felt over slab and then screw down 3/4 cdx for the flooring to be nailed to. This house is about 12" above grade. Has anyone had issues with the application or advice for doing it another way? I'm not installing the floor, just the plywood. Thanks.


----------



## Sampietro (Apr 14, 2011)

I have scene 1" rigid foam installed and taped then 3/4"ply tapcon down on top of the foam. It looked like a good system to me.


----------



## jamestrd (Oct 26, 2008)

i would add this..make sure the plywood is dry and acclimate it to the areas as any other lumber..,

2 if you use felt paper, you are you first prime,then use cutback adhesive,then lay felt one way and criss cross the other.
then skim again with cutback,
lay ply and fasten by shots or preferred.

otherwise, simply, 6 mil, CDX in opposite direction to floor install direction...leave spacing for expansion between sheets....
use only 11/2" cleats/staples for floor install as to not penetrate retarders..

these systems have worked time and time again, in commercial residential for generations..
you will get lots of feedback..but bottomline is it works.the ones that don't work are usually the ones who really didn't follow the methods.


----------



## JesseCocozza (Aug 20, 2011)

jamestrd said:


> i would add this..make sure the plywood is dry and acclimate it to the areas as any other lumber..,
> 
> 2 if you use felt paper, you are you first prime,then use cutback adhesive,then lay felt one way and criss cross the other.
> then skim again with cutback,
> ...


So axe the felt paper. Roll out some 6mil plastic. Tapcon or shoot down plywood, and call it a day? 

If you go with felt, the primer your referring to is to seal the slab? Not necessary with the 6 mil application? 

Forgive my ignorance. I'm a carpenter, not a flooring guy. I'm prepping the floor for the installers and I don't want to be the reason for a failed floor.


----------



## ohiohomedoctor (Dec 26, 2010)

JesseCocozza said:


> Working on a house where nail down wood flooring has been chosen. In the past I've ran 30# felt over slab and then screw down 3/4 cdx for the flooring to be nailed to. This house is about 12" above grade. Has anyone had issues with the application or advice for doing it another way? I'm not installing the floor, just the plywood. Thanks.


Thats how we have done it.


----------



## rusty baker (Jun 14, 2008)

I assume you have moisture tested to make sure you won't have mold growth?


----------



## ohiohomedoctor (Dec 26, 2010)

rusty baker said:


> I assume you have moisture tested to make sure you won't have mold growth?


Every time :thumbsup:


----------



## JesseCocozza (Aug 20, 2011)

rusty baker said:


> I assume you have moisture tested to make sure you won't have mold growth?


Not being a floor guy, could you give me a little
Insight on how to go about testing this.


----------



## Big Shoe (Jun 16, 2008)

I've seen the plywood cut to 4'x4' squares and gapped slightly. Also it was acclimated for a couple weeks prior to installation. Makes some sense to me, but I'm not an expert on this. 

Majority of guys just put down 4x8's. And some shoot it down with coil nails.

Good Luck!


----------



## tileman2000 (Feb 14, 2011)

You can buy moisture testers at your local big box stores.


----------



## ohiohomedoctor (Dec 26, 2010)

Our flooring store comes out and takes the readings. For us its great because we get their approval to install their goods.


----------



## griz (Nov 26, 2009)

Have the floor installer sign off on the substrate.


----------



## ohiohomedoctor (Dec 26, 2010)

griz said:


> Have the floor installer sign off on the substrate.


What floor installer in his right mind would certify an installation he had nothing to do with. Have the flooring company do the whole project if thats the direction your going.


----------



## griz (Nov 26, 2009)

Flooring company calls all the shots on the substrate install.

That way any problems are theirs.:thumbsup:


----------



## ohiohomedoctor (Dec 26, 2010)

griz said:


> Flooring company calls all the shots on the substrate install.
> 
> That way any problems are theirs.:thumbsup:


I get it now. Sorry. :sad:


----------



## Big Shoe (Jun 16, 2008)

All the homes I've worked in the guys installing the finish floor put the subfloor down.

Jesse, I would just do it exactly the way it is spec'd to you, to the ''T''

That' why I use ''as/per'' on my invoices. 

Sarasota has the best beaches! :thumbsup:


----------



## JesseCocozza (Aug 20, 2011)

Big Shoe said:


> All the homes I've worked in the guys installing the finish floor put the subfloor down.
> 
> Jesse, I would just do it exactly the way it is spec'd to you, to the ''T''
> 
> ...


Yeah, I'm big on the "as per" also. I've used this method in the past for a bedroom here there,
Just not the whole house. The flooring guys are swampped and asked if we could do it to speed it up. I'm going to get the moisture tester today and have at it. A/c is going in as soon as we finish with the plywood so we can start acclimating the flooring material for a
Week or so. I appreciate everyone's input!

And yes, our beaches are beautiful! Currently holding the #1 beach in the nation award! 

Where in fl are you?


----------



## JesseCocozza (Aug 20, 2011)

Ok so I got a pinless moisture meter this morning. We currently don't have the a/c on. It's getting installed Wednesday. Please forgive my ignorance. The slab is reading anywhere from 60%-73%. Is this because the humidity in the air is settling on the slab? Should I expect to see that number drop to a safe level when the a/c is turned on? Current weather here is 70 * F with 88% humidity (not trying to rub it in. ) Again, we weren't installing any finished flooring until a week or do after it acclimated in the AC. I was hoping to get the plywood down before though. Thanks in advance for the feed back.


----------



## ernesto (Apr 11, 2011)

You cannot reliably test the moisture in concrete with a non-invasive meter or concrete meter. You should be doing a CaCl and or ASTM F-2170-11. Also watch the video on dewpoint

http://www.concretemoisture.com/construction/rh-testing-practices/

http://www.youtube.com/watch?v=NZ4Heg17HSk&feature=youtu.be


----------



## Rich D. (Oct 14, 2011)

Wheres ernesto?


----------

