# What should I use to fill large divets and small gaps in OSB subfloor?



## jsand (Nov 19, 2011)

I'm installing subfloor on which I intend to put Drop-and-Done vinyl directly on top. The Drop and Done is thin (3/16") and very flexible, so I assume we'll feel every little flaw in the subfloor. There are these "wonderful" divets in the ends of every sheet of T&G OSB from HD (picture attached) that need to be filled. :vs_mad:



My question is - what product should I use to fill these? The divets are 3/8" wide and ~1/2" deep. 



Also- how anal should I be about filling small gaps where the OSB didn't quite fit together - some gaps are maybe 1/4" wide, most are ~1/8", but otherwise the joints are flat.


Thanks!


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## mark sr (Jun 13, 2017)

While I'm not familiar with that flooring it's commonplace to first install 1/4" underlayment over the subfloor and then put the vinly over it. The joints would be staggered from the subfloor joints.


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## Yodaman (Mar 9, 2015)

Bingo, what Mark said. You need underlayment for vinyl flooring. And when done, seams need to be super smooth. Deep nail divits filled. These thin vinyl floors telegraph everything from below. Especially in traffic areas.


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## jsand (Nov 19, 2011)

Thanks for the advice, 1/4" ply is easy enough. Any thoughts on what I should fill any holes and gaps in it with? Wood filler is so expensive...maybe DAP Plastic Wood, or would that be overkill?


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## Yodaman (Mar 9, 2015)

jsand said:


> Thanks for the advice, 1/4" ply is easy enough. Any thoughts on what I should fill any holes and gaps in it with? Wood filler is so expensive...maybe DAP Plastic Wood, or would that be overkill?





Floor leveler. Usually comes in powder form, mix up what you need, apply with a putty knife. let cure thoroughly, sand lightly. Ready to tile.


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## RRH (Nov 24, 2016)

jsand said:


> Thanks for the advice, 1/4" ply is easy enough. Any thoughts on what I should fill any holes and gaps in it with? Wood filler is so expensive...maybe DAP Plastic Wood, or would that be overkill?


Use the right product.
Ardex feather finish is best. Or if from the box store try.
https://www.homedepot.com/p/Custom-...atching-and-Finishing-Compound-SF10/100152565

Also goggle the nailing pattern for the 1/4" underlayment. By the time you mess with the cost and installation.
You are not far from the cost of just installing a better floor without the underlayment needed for the thin sheet vinyl.

Look at the lifeproof LVP at homey depot.
Still should use a patching compound.
Anyway gives you something to think about.

Next time pass up the OSB T&G and get the Advantech T & G which already has a good finish.


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## mark sr (Jun 13, 2017)

I have used a setting compound like Durabond to fill the seams and staple holes on the underlayment but then I do more walls than I do floors ..... and I always have some Durabond on hand.


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## Marson (Jan 26, 2018)

And FYI those "divots" are standard on OSB subfloor plywood. They are drainage grooves so water doesn't get trapped in the butt seam during rain (new construction). Yes, use underlayment and next time use advantech or an underlayment grade 3/4 plywood.


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## chandler48 (Jun 5, 2017)

> They are drainage grooves


Unless it is something proprietary, I gotta call the BS police on this one. Seldom is OSB used as a subflooring during construction so weep holes would not be factored in the manufacturing. Advantech is made for that and should be used. Durabond is a good filler and quite a bit less expensive than wood filler. I wouldn't worry about the boogers on the subflooring, since it will be covered by the underlayment.


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## 3onthetree (Dec 7, 2018)

Marson said:


> And FYI those "divots" are standard on OSB subfloor plywood. They are drainage grooves


That's whack!!
Most likely this sheet was top or bottom of the pallet, metal band cut a groove.

Side note, I only see OSB for subfloor on a typical house, 1/2 price of Advantech and the roof is usually up quickly. 

On this new thick vinyl planking, supposedly you can patch/sand and install over the exist T&G. Personally, I would always install "underlayment" (not 1/4" plywood), as rough-in framing ain't pretty. Especially when you put glue down. It's costly, but a good APA rated underlayment will save you bumps (literally) down the road. APA because its going to get wet from the glue.


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## Oso954 (Jun 23, 2012)

Here is one example of a OSB subfloor drainage hole.
Note that the edge of the OSB has been inlet slightly to allow for drainage.


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## Yodaman (Mar 9, 2015)

Qucik tip on installing the thin underlayment. A narrow crown pneumatic stapler will make the job go so much easier. The nailing grid on these thin sheets is between 4 to 6" and closer around the perimeter. So you are easily looking at 150+ fasteners per sheet.
I would concede that a ring shank flooring nail is the very best fastener choice, but the narrow crown staples are adequate and so much quicker.
Do not use glue, you might want to pull it up some day.


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## 3onthetree (Dec 7, 2018)

Yodaman said:


> Do not use glue, you might want to pull it up some day.


I think this product uses a pressure-sensitive glue just to keep it from sliding, so it pulls up. I try to stay away from these new-fangled fancy-dancy products until they've been time-tested anyway.

That "drain" hole, how does that work in T&G, especially glued? Why would a ply manuf. design for POOLING water on a temporarily exposed subfloor? I have to look this one up, I still think its whack.


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## jsand (Nov 19, 2011)

Actually, they do look like drainage slots. There are two on every single board and they are very regular. They are on the 4' ends, not the T&G sides. Seems very odd to me too.


Yes, the Drop and Done uses a pressure sensitive glue, and only around the perimeter so at least I wouldn't be applying wet glue everywhere. I'm really kicking myself now for going with OSB - I don't know why I thought it was fine, but I spent a LOT of time reading about subfloors (mostly focused on damp basement approaches) - I don't remember reading about Advantech or using treated ply. I read more than one place that OSB is fine, but who knows what qualifications those folks had! Or maybe I was reading what I wanted to read since OSB is so much cheaper.


So .... now my problem is that if I raise the floor another 1/4", my lower stair step is going to be out of code. Not to mention the time and another $500 (both relatively minor). 



Thoughts/experience on other approaches to making the OSB okay? Maybe skim coat with a sealant? I don't really understand how it can expand and contract enough to cause gaps/buckling when it's screwed down, but I recognize I'm a naive newbie.


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## jsand (Nov 19, 2011)

Also, before the obvious question comes up - we did not put OSB in contact with the basement foundation. We did a lot of research and ended up installing a dimpled plastic underlayment on the concrete to allow vapor pressure to release from under the subfloor (similar to DMX) with the OSB over that. Basically, creating a better version of Dricore.


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## 3onthetree (Dec 7, 2018)

I've never used this thicker product, but I did install a temporary sheet vinyl floor that was carpet-taped to the underlayment (which was not smooth-seamed). I was afraid the ringshank nails or seams would show, but they didn't. I did not, however, like the slight bubbling from either infiltrated air, heavy furniture, or house movement. These "floating" vinyl floors are great on concrete, I'm not sold yet on top of wood regardless of thickness.

It should be thick enough to hide any slight imperfections in the OSB, so leveller like others stated. I use subfloor glue in the non-T&G sides gaps as a backer rod.

My insistence on using underlayment for anything but 3/4" hardwood or carpet comes from years of removing other's flooring put directly on the subfloor. Houses always get remodeled, and I like to see an intact subfloor nailing patterns and all. But that was before you stated the subfloor is on a dimpled membrane in the basement, so I'm not sure an underlayment would matter much here.


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## 3onthetree (Dec 7, 2018)

Ah, those drains are on the big guys' premium products. Don't come across those as I only get to see cheap OSB eveywhere since those came to market.


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## Yodaman (Mar 9, 2015)

3onthetree said:


> I think this product uses a pressure-sensitive glue just to keep it from sliding, so it pulls up. I try to stay away from these new-fangled fancy-dancy products until they've been time-tested anyway.
> 
> That "drain" hole, how does that work in T&G, especially glued? Why would a ply manuf. design for POOLING water on a temporarily exposed subfloor? I have to look this one up, I still think its whack.





I was referring to the underlayment, not the finished floor. The whole post was related to installing underlayment.


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## Marson (Jan 26, 2018)

3onthetree said:


> That's whack!!
> Most likely this sheet was top or bottom of the pallet, metal band cut a groove.



No, they are drainage grooves. I think the OP has the sheet installed upside down though. The grooves prevent pooling of water on the end of the sheet. Also Chandler, OSB subfloors are very common in many parts of the country.


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## 3onthetree (Dec 7, 2018)

Marson said:


> No, they are drainage grooves.





3onthetree said:


> Ah, those drains are on the big guys' premium products. Don't come across those as I only get to see cheap OSB eveywhere since those came to market.


Yep, learn something new everyday^^!


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## carpdad (Oct 11, 2010)

Another underlayment plus the floor is actually over 1/2", although technically out of code for riser but could get used to it.
But smooth underlayment is called for the kinds of flooring that are very thin. Traditional vinyl sheets or tiles that are little thicker than 1/16. 3/16, even if vinyl, seems thick enough to bridge some gaps, although maybe not osb edge joints that are different thickness. You could get the tiles and lay them without removing the glue protection and try walking over them. Also what does the manual say? You could even rent a floor sander and smooth down the osb. Bondo may be very stable filler for your situation.


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## Yodaman (Mar 9, 2015)

carpdad said:


> Another underlayment plus the floor is actually over 1/2",



1/4 underlayment actually measures about .200 plus or minus a little. Add in the 3/16 (.1875) floor and it comes to .3875, a little over 3/8". I honestly doubt anyone would notice the first step being 3/8 shy. 

Yes some building inspectors can be anal, but my inspector doing final walk through's has never measured a stair step. Just walked up and down them to see how they felt. 

That said, is there going to be a final inspection hear? 

It's very doubtful that home inspector would flag a stair step being low by 1/8".


This is only MHO, I would not be worried about the stair step and use the underlayment. OSB just makes crappy underlay for vinyl. It compresses in traffic area's, tiles lift from delamination, and heaven help you if a little water gets spilled.


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## Somebody Scream (Nov 25, 2020)

jsand said:


> I'm installing subfloor on which I intend to put Drop-and-Done vinyl directly on top. The Drop and Done is thin (3/16") and very flexible, so I assume we'll feel every little flaw in the subfloor. There are these "wonderful" divets in the ends of every sheet of T&G OSB from HD (picture attached) that need to be filled. :vs_mad:
> 
> 
> 
> ...





jsand said:


> I'm installing subfloor on which I intend to put Drop-and-Done vinyl directly on top. The Drop and Done is thin (3/16") and very flexible, so I assume we'll feel every little flaw in the subfloor. There are these "wonderful" divets in the ends of every sheet of T&G OSB from HD (picture attached) that need to be filled. :vs_mad:
> 
> 
> 
> ...


I'm sure your project is long completed by now but for others having same situation or for a future project. Dap makes a product exactly for that called Flexible Floor Patch and Leveler. For plywood, subfloors and concrete.


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## Gibbyspena (Jun 19, 2021)

Somebody Scream said:


> I'm sure your project is long completed by now but for others having same situation or for a future project. Dap makes a product exactly for that called Flexible Floor Patch and Leveler. For plywood, subfloors and concrete.


Thank you


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