Resurfacing OSB subfloor?

[Steve Mathews]

While pulling out glued down wood flooring on a second floor remodel the top surface of the OSB subfloor came out with it. I was planning to pull out the badly damaged sections but it will be somewhat difficult because construction adhesive was used to attach the OSB to the truss joists. Is it possible to use some type of flycutter to route a new surface on the OSB about 1/4" deep and add an underlayment? Alternately is there another way of handling the problem?

[Erik Loza]

I've only ever seen it ripped out completely (sawzall) but curious to know if there's an easier solution.

Erik

[George Bokros]

Luan over the osb?

[Paul F Franklin]

If the damaged areas are anywhere near half of the total area, just bite the bullet and rip it out and put down T&G plywood subfloor. You will have to add blocking anywhere the edge of the new material isn't supported for more than 16" or so. If there is only a small amount of damage, use a trowelable floor patch on the damaged areas to get a reasonably smooth surface and then cover with 1/4" APA rated underlayment, glued and screwed or stapled down. Most luan isn't APA rated for underlayment, a lot of it has interior voids.

[Mark Bolton]

I would just buy a few bags of floor leveler, float it all out flat, and toss as thin a substrate as needed over top.

Any foolishness with routing or ripping out will be a colossal nightmare and if the PB was glued to anything below your going to chase it all the way to the poorhouse.

Get whatever off, scrape / brush it clean, mix up some batches of soup, float it on, float it out, skin it, and walk away.

[Mike Soaper]

I guess in theory a router and router sled like those used for flattening slabs might be used. As to if it's practical I suspect it depends on how much of an area you need to do or if the resultant built up floor would be strong enough

[John C Bush]

We used thin underlayment(???) ply to cover old (flooring guy suspected asbestos--OK with regs as undisturbed and easier than removal)
tile and layed new carpet and Marmoleum--Commercial bldg

[Steve Rozmiarek]

Like Paul and Mark said, skip the thought of milling it. It's probably screwed down and guaranteed that a milling process will hate them. Why are you removing glued down subfloor? Usually if it's glued down, it's structural and it should stay put.

[Steve Mathews]

Like Paul and Mark said, skip the thought of milling it. It's probably screwed down and guaranteed that a milling process will hate them. Why are you removing glued down subfloor? Usually if it's glued down, it's structural and it should stay put.

What was removed was wood flooring (planks) glued to the OSB subfloor. I have no idea why it wasn't just nailed to the subfloor. The room is a relatively small 10' x 15' bathroom. Only about half of that area is affected. I'm concerned that some of the top layer of OSB has weakened the floor. I don't think floor leveling compound alone will bring back any of it. Since OSB is somewhat of a composite is there a mix of epoxy with fibers that would bind to the OSB and level it at the same time?

[John Grossbohlin]

What was removed was wood flooring (planks) glued to the OSB subfloor. I have no idea why it wasn't just nailed to the subfloor. The room is a relatively small 10' x 15' bathroom. Only about half of that area is affected. I'm concerned that some of the top layer of OSB has weakened the floor. I don't think floor leveling compound alone will bring back any of it. Since OSB is somewhat of a composite is there a mix of epoxy with fibers that would bind to the OSB and level it at the same time?

I suspect that the flooring was glued as OSB generally doesn't take and hold staples and nails as well as plywood or solid wood. Given that part of the OSB has been ripped off in removing the flooring it no longer meets the span ratings... From your description it doesn't sound like there is a lot that should be removed... As such I'd tear it out and replace it. Do this particularly if tile is being installed over it--you don't want the floor to flex as the grout will crack. To remove the OSB/Glue place a 2x4 flat on the floor, over the length of the joist (not perpendicular to them) to span the low/damaged areas. This gives you a flat surface to work from... Then run a circular saw over the 2x4 over the length of the joists with the depth set to the sum of the 2x4 and OSB (e.g., 1 1/2 + 1/2 -- measure it!!) such that you just skim the top of the joists without cutting into them. You will have to take multiple parallel passes to get all the glue... you'll figure it out! Use a demo blade that will cut nails/screws. For example Dewalt DW3191 https://www.amazon.com/DEWALT-DW3191-Cutting-Diamond-Knockout/dp/B0000225LP I've done this... it works. I hope the description if adequate!

[Joe Jensen]

I agree with those who said to rip it out. Most houses are built to min spec. OSB flexes way more than plywood. Likely a thin layer on top of the bad OSB would be too weak

[Mike Soaper]

1/4" 5 ply hardwood plywood come to mind as maybe being strong enough to work, like finnish/aircraft birch plywood, appleply, or a good baltic birch plywood, or maybe a 3ply marine ply.

fwiw I've seen a 50? yr old manufactured house located at a beach that had particle board subflooring, the floor also had some waves because the particle board had sagged between the floor joists.

[Steve Rozmiarek]

What was removed was wood flooring (planks) glued to the OSB subfloor. I have no idea why it wasn't just nailed to the subfloor. The room is a relatively small 10' x 15' bathroom. Only about half of that area is affected. I'm concerned that some of the top layer of OSB has weakened the floor. I don't think floor leveling compound alone will bring back any of it. Since OSB is somewhat of a composite is there a mix of epoxy with fibers that would bind to the OSB and level it at the same time?

Ahh, I see. I hate glue down flooring. They should have put a layer of underlayment over the OSB subfloor that they actually glued the flooring to. John's sawing stick works pretty well. The OSB should be glued to the joists with a good adhesive, usually PL400 around here. It will fight you a little getting that bond broke so make sure you don't mess up the joists. TJI (I joists) don't tolerate trauma to the top chord well. Alternative to all this is just to self level and add another layer of underlayment. They probably glued the hardwood to the OSB because they didn't want to get a higher floor that underlayment would have caused. However, if you are going back with a thinner floor like vinyl, you can afford another layer. Tile would require another layer of underlayment to, 3/4" sub plus 1/2".

[Steve Rozmiarek]

1/4" 5 ply hardwood plywood come to mind as maybe being strong enough to work, like finnish/aircraft birch plywood, appleply, or a good baltic birch plywood, or maybe a 3ply marine ply.

fwiw I've seen a 50? yr old manufactured house located at a beach that had particle board subflooring, the floor also had some waves because the particle board had sagged between the floor joists.

There is a big difference between that old particle board (junk) and the OSB subfloor of recent years. Trufloor, Advantech and the like are stronger than plys in my experience.

[Frank Pratt]

I agree with those who said to rip it out. Most houses are built to min spec. OSB flexes way more than plywood. Likely a thin layer on top of the bad OSB would be too weak

No, actually OSB is stiffer than plywood up to the point of failure. Plywood does have higher ultimate strength though.

[Jim Becker]

What you propose would be difficult. If the subfloor is otherwise stable/safe, and since it's well, a subfloor, it doesn't need to be pretty. Fill the divots with mastic or something and if you really feel the need, cap that with 1/4" material before moving on to your new floor surface.

[johnny means]

I wouldn't spend any effort on trying to salvage a $10 sheet of OSB. Cut it out and throw in a new piece.

[mreza Salav]

cut it into smaller pieces with shallow cuts, remove screws and clean the glued areas to I-joists. Put a new one down with glue/screwed to joists. Cleaner/better job.

[Carol Schnell]

I live in a house built in the 40's. I decided to get rid of the carpet in a bedroom so I could glue down engineered flooring. Under the carpet I found ¾ " diagonal plank yellow pine wood with gaps between the boards. There is a crawl space under the house with high quality plastic as a moisture barrier over the dirt. Should I remove the plank and replace it with 3/4" plywood? If I add plywood over the plank, the floor will be considerably higher than the adjacent wood at the doorway. The floor is relatively flat and would need minimal leveling. Is Ardex cement-based underlayment the best product for that? Do I need an underlayment paper or felt over the plywood? Do I need to silicone the cracks between the plywood? As you can see, I need lots of advice. I appreciate any help you can provide. Thank you.

[Jim Becker]

Carol, there is no need to remove the plank subfloor if it's structurally sound. You should use whatever the engineered flooring manufacturer specifies between the subfloor and the engineered flooring you choose as many products have some form of preferred underlayment that provides cushioning, etc. That will effectively close any of the small gaps in the existing subfloor. Now if that subfloor is in poor condition where more than limited repairs are required, it might be worthy of replacing it with modern materials.

[Tom Bender]

Hi Carol
What Jim said is solid. And,

It's important to keep the outside out of your crawl space. A bug inspection is money well spent. Maintain your gutters and lot drainage. Previous owners may have been vigilant and you can not afford to do less.