# 3/8" plywood as underlayment



## joecaption (Nov 30, 2011)

No glue needed, make sure the seams do not line up with the seams below.
Use A/C plywood.
I would not screw it, it's going to leave dimples, the fastest way is to use a pneumatic staple gun with narrow crown staples.
You can also use underlayment nails, just a whole lot slower.


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## Kaveman42 (Dec 27, 2013)

I would prefer to stay away from staples and nails if possible. I don't want to squeaky floors down the road. Is the dimple a big issue for glued eng. hardwood?


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## joecaption (Nov 30, 2011)

How's the flooring going to be able to lay flat and make 100% contact with the underlayment if it's full of small humps?
Try putting some screws into a sheet of plywood then run a drywall knife over the surface and see how it works out.
Only way there would be squeaks is if the subfloor below it is flexing.
I've been doing it with nails or staples for the past 30 plus years and never had a squeak.
There near impossible to pull out without destroying the plywood.


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## JazMan (Feb 17, 2007)

Kaveman,

Joe is right. If you ever get squeaks, the underlayment will not be the source. It'll be the subfloor/joists connection. 3/8" underlayment isn't structural, and so adding a bunch of screws isn't gonna help make the floor much stiffer. I can see you not wanting to use underlayment staples since you don't have the right tool. Use underlayment nails instead. They look very much like drywall nails.

Jaz


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## Kaveman42 (Dec 27, 2013)

I believe my father in-laws has a staple gun that came with his porter cable nail gun set. What type of staples should I be looking for to see if they would fit his gun?


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## joecaption (Nov 30, 2011)

http://www.newwoodworker.com/reviews/pcns150a.html
One like this will work.
I use 1-1/4 long staples.
Using one of these set in bump mode you can staple a whole sheet in about 2 min. or less with no having to crawl around on your knees.
It needs to be stapled every 4" on the edges and from 6 to 8" in the field.


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## Kaveman42 (Dec 27, 2013)

joecaption said:


> No glue needed, make sure the seams do not line up with the seams below.
> Use A/C plywood.
> I would not screw it, it's going to leave dimples, the fastest way is to use a pneumatic staple gun with narrow crown staples.
> You can also use underlayment nails, just a whole lot slower.


Hi Joe,

I see you mentioned using AC grade plywood. I had no luck finding AC grade plywood at Home Depot or Lowes at the 3/8" thickness. They seem to only have CC grade. Since I have 1" inch thick subfloor already, would I be able to get away with CC grade? Are there any issue's I would be facing if I used CC as underlayment?


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## ront02769 (Nov 28, 2008)

You seem to be looking at this from the wrong angle. You appear to already have an adequate structural base on which to install that finish product. All you really want to do is to raise the height, hence adding 3/8" plywood. While ther are different grades of plywood in terms of glue types, # of plys, type of wood, etc., the terms a/c, b/c! whatever merely refer to the Degree of FINISH on the sides. An "a" side will have knots filled, be sanded smooth, etc. whilst a "d" side will be rough with inot holes etc. in the top ply. Not so much to do with structural strength. Maybe just ask for 3/8 underlayment and you should get a product specifically designed for that, staple down, and done and done. Ron


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## joecaption (Nov 30, 2011)

The issue with using the wrong plywood is a CC grade would have voids in the core ply's.
It needs to be voids filled and exterior glue, underlayment rated.


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## TarheelTerp (Jan 6, 2009)

Kaveman42 said:


> I see you mentioned using AC grade plywood.
> I had no luck finding AC grade plywood at Home Depot or Lowes...


Find a real lumberyard.


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## Anti-wingnut (Oct 18, 2009)

joecaption said:


> The issue with using the wrong plywood is a CC grade would have voids in the core ply's.
> It needs to be voids filled and exterior glue, underlayment rated.


You are correct that there are special underlayment grade plywood, usually 1/4" AC. But since the OP is putting down 1/2" net hardwood, I don't think worrying about voids is as warranted as with putting down VCT or sheet vinyl.


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## ront02769 (Nov 28, 2008)

joecaption said:


> The issue with using the wrong plywood is a CC grade would have voids in the core ply's.
> It needs to be voids filled and exterior glue, underlayment rated.


He is putting down hardwood, not sheet goods or vinyl tile. Only purpose of his extra layer is to bring the floor to height. No worries. Ron


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## Kaveman42 (Dec 27, 2013)

ront02769 said:


> He is putting down hardwood, not sheet goods or vinyl tile. Only purpose of his extra layer is to bring the floor to height. No worries. Ron


So does that mean I don't need AC rated?


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## ront02769 (Nov 28, 2008)

Obviously different opinions. I would not worry about. Ron


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## Kaveman42 (Dec 27, 2013)

Im planning on ordering the crown stapler for my project. SInce I only need to install 1 1/4" staples can I get this gun?

http://www.amazon.com/DEWALT-D51420K-1-Inch-4-Inch-Stapler/dp/B000HQ4QKW/ref=sr_1_4?ie=UTF8&qid=1399341371&sr=8-4&keywords=1+1%2F4+crown+stapler 

or do I still need to buy 1 1/2" stapler?

http://www.amazon.com/DEWALT-DWFP12232-18-Gauge-2-Inch-Stapler/dp/B00BDPJ2M8/ref=pd_cp_hi_0

There is like a $30 difference between the two.


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## ront02769 (Nov 28, 2008)

Not sure of your question. But if you are going to be shooting narrow crown staples that are 1 1/4" long, they won't fit in the first gun that you listed. Ron


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## Kaveman42 (Dec 27, 2013)

Thanks Ron, I just realized it was 1". I'll try to pick one up from lowes tonight.


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