[afeddy05]

We removed ceramic tile, cement board and linoleum to expose subfloor due to water leak. We need to add plywood to exisiting subfloor. My question is does it have to be "plywood underlayment" or can it be 1/4" or 1/2" OSB?

Does this get screwed and glued (with liquid nails) as well?

 

[chandler48]

What thickness is your existing subflooring? If 3/4", then an additional 1/2" plywood is usually sufficient. What will be your final flooring? If tile, let us know the size of your joists, and the total unsupported span under the area. If there are post and beams, etc.

You would use NO glue, and install the plywood with screws, intentionally missing the joists, allowing for a "slip" factor between the two layers. Before you start, ensure the existing subflooring is screwed to the joists to eliminate the possibility of squeaks.

 

[afeddy05]

W e are putting down lifeproof plank flooring.

Existing subfloor, I believe is 3/4” plywood and is nailed down. With the tile we never ran into issues with squeaky floor though

 

[chandler48]

It is always advised to have 1 1/4" of subflooring for that "substantial" feeling under foot. The lifeproof adds no height nor weight appreciably, like tile would, and should make a nice floor.

 

[ktownskier]

Yeah, what he said!!

OSB is for the initial sub-floor, but for the second layer, I like plywood. With the X designation as in ACX or CDX which means the glue is exterior rated.

Plywood holds fasteners better. I fell that OSB doesn't hold as well.

 

[joecaption]

Never use CDX as an underlayment!
It's full of voids in the plys!
It would be fine to add some screws to what's there now, but I'd never use screws to attach the underlayment.
Reasons being, as a screw goes in it tends to try and lift the underlament before pulling it down, it will leave raised dimples where the head compresses the wood, and voids where the heads of the screws are, it's far slower, and far more expensive.
Keep in mind this needs to be fastened every 4" on the edges, and from 6 to 8" in the field, so that would be a whole lot of screws.
If I did use screws I'd go back over with a random orbital sands, vacuum, then go back and fill all the screw heads so there was no chance the screw heads would mirror through the flooring.
I use a narrow crown staple gun, that way the heads are near invisable.
I've done dozen like this and never once had a call back.

 

[ktownskier]

@joecaption,

I didn't mean to say that you should use CDX, I just used that as an example. I would prefer to use ABX, ACX or BCX.

As for screws, you are correct. At least for regular screws. You need to find screws that don't have threads for the last portion equal to the thickness of the material you are trying to attach. That type of screw will suck the material down to substrate.

I agree with you on the stapler though. I prefer that as well. you can alternate the staples so that it draws the material down as well. And you can staple all you want. I have used a full stick of staples for a 4x8 sheet.

 

[afeddy05]

Do you have an example of the type of stapler and staples? I’ve never applied it that way before

 

[afeddy05]

Just confirming I don’t glue it or use any type of adhesive? When you were saying no screws I figure that meant I should use adhesive ONLY.

 

[ktownskier]

Just confirming I don’t glue it or use any type of adhesive? When you were saying no screws I figure that meant I should use adhesive ONLY.

You would use nails or staples.

If nails, you would use any nail other than a common nail which has a smooth shank as you want it to grab into the sub-floor.

Staples only work if they are fired by air, or some other assisted device. A whacker type stapler won't work.

If you have a compressor, then go with air. If you don't have a pneumatic stapler, get one, they do a lot of things. If you don't have a brad or finish nailer, buy a set that includes all three. Husky sells one and I am sure that Kobalt does too.

If you don't have a pancake compressor, you can guy a kit that includes a compressor with nailers/stapler for around 150-200.

A good deal if you are doing any kind of reno or remodeling work. I use mine all the time.

 

[chandler48]

A narrow crown 7/32" x 1 1/2" staple will work fine if you don't want to use screws. Spax and GRK makes screws that won't stand proud and hold exceptionally well. I wouldn't use regular drywall or even decking screws without a serrated under head to dig in.

 

[afeddy05]

A narrow crown 7/32" x 1 1/2" staple will work fine if you don't want to use screws. Spax and GRK makes screws that won't stand proud and hold exceptionally well. I wouldn't use regular drywall or even decking screws without a serrated under head to dig in.

I maybe more confused at this point. I am hearing screws and no screws, staples, etc. I don't have a nail gun (but could get one that shoots finish nails and staples). But it sounds like I could use Spax or GRK screws?

Can you explain why its a NO to adhesive?

Should I add screws to existing sub floor first?

 

[chandler48]

Older subflooring tended to be installed with smooth shanked nails. Yes, I would back that up with screws into the joists. The existing subflooring and the new subflooring layer cannot move as one entity. They will swell and contract (ever so slightly) independently. So you don't glue them together and you install your fasteners to miss the joists where the initial subflooring is attached.

If you plan on buying a nail gun, buy a framing gun and 2"+ ring shanked nails and install them in the second layer. If you can get a narrow crown stapler, all the better. Two legs hold better than one.