How to level an uneven OSB subfloor before laminate?

[Blanky]

I've googled this extensively. What I've found is many people asking the question and very few people giving any actual idea on how to remove the imperfections in OSB.

Laminate requires no more than a 1/16" unevenness over 40", which is exceedingly flat. My guess is a lot--probably even the majority--of laminate jobs installed exceed this. Are they having problems? I don't think so, but possibly could be used to reject a warranty claim.

Anyway, my floors are in good shape mostly, with up to 1/8" over 40" which I intend on ignoring. However, I do have a section with 1/4 or 3/8" (the result of a high joist, which makes either side low). The question is: how to raise those other sides up (sanding down the OSB over that part of the joist is an option, but a lot of work, and could compromise the floor;require re-screwing/nailing).

Ideas online:

1) Leveling compound. Note: a lot of this stuff isn't wood approved and could make a hellacious mess around the walls
2) Build up with roofing tiles and/or tar paper. Concern: Off-gassing. These products are not intended for interior installs and I have no idea how safe they are.
3) Install 1/4" ply where needed and feather its edges with a belt sander. This seems the safest and possibly smartest to me.

Any other ideas?

*UPDATE 4/27/2015*

Not going to bump thread right now, but in case anybody stumbles upon this thread in the future, some thoughts after much research:

1) Sanding high spots on a wooden floor is crazy. Some people advise it, but it's a fool's errand. If significant wood material need be removed, a $70 electric planer will chew it up like nobody's business. Obviously, most such unevenness is at a joist, so you'll need to remove the nails first. You could alternatively raise a lowered joist if it's accessible from below and not glued in by shimming it, or remove the piece of subfloor and grind just the joist itself down (way quicker than griding down a larger piece of OSB where it crowns the joist). I didn't do this; instead I've so far ground down some extra thickness on the top of some OSB (not so much it's appreciably weakening anything).

2) Self-leveling OSB (or ply) is often recommended and is almost always against all manufacturer directions for self-leveler. All self-leveling compounds, from TEC, to Henry/Ardex, to Custom call for priming + lath/mesh + leveler, and all have a minimum thickness when used on wood. It is only to be used when leveling an entire room, and remember level doesn't matter for a laminate floor anyway; only flatness; a sloped but flat floor is fine.

3) 30lb felt is 1/16" thick. It is great in one layer, but multiple layers may make a diaper sound Nail down floors like hardwood seem to work well with felt and shingles, and many pros use them in that scenario.

4) The only trowelable patching compound I've found that specifically says OSB is approved is TEC Feather finish or silk finish or something--can't quite remember exactly--after a layer of Redgard. Unable to find any, I called TEC and the guy said he thought SpeedFinish would be highly similar due to its large polymer level, though the box does say OSB isn't recommended (exterior ply is fine). I think it would work, and skyking has had luck with it. My home's OSB is printed with Exposure 1. This isn't exterior, but it means it can tolerate some wetting during construction, so I doubt any patch compounds would cause it to swell in their short curing time (several hours).

5) Henry 549 FeatherFinish at home depot costs $17 for 7 lbs, but it is owned by Ardex and many online seem to say Ardex FeatherFinish and Henry 549 are the same--and also that Featherfinish is the best stuff there is. As such I got the Henry branded stuff and tested on OSB. I applied to the rough side of OSB after keying it in with a trowel tightly. I had zero swelling and after it cured tried flexing the OSB, hammering it, plying it off. It tolerates all this abuse really, really well, so I have patched many low spots with it. Be sure that once it's troweled on you wait maybe 30 min for it to start curing, then go over the control joints between OSB with the trowel, re-building the gap between the boards. Always use a mask when mixing stuff like this, the powder is nasty stuff. I found it easy enough to work with, very similar to ceramic tile thinset, though maybe only 20 min or so pot time.

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I still think most people have floors out of spec, apply their laminate, and seem to be fine. But, being completely inexperienced with using it, I'm not positive of that, so I have to be an idiot and research it almost certainly beyond the point I should, due to complete lack of experience.

 

[Greenman]

My guess is that most people ignore that spec, I know I did in my own house.
Obvious humps or dips should be addressed, spending 40 hours perfecting a sub floor is absurd.

Edit: What you wrote just clicked (it's early). I joist with a hump is going to be tough to fix, filling in around it just makes a bigger hump. I'd pull the subfloor and cut the joist down.

 

[edro]

I used tar paper, rosin paper and thinset to fill in dips and taper down abrupt ridges.
I did this under 3/4" oak floors that were nailed in place though.
I'm not sure I would trust tar or rosin paper under laminate flooring since it isn't nailed down. It might feel spongy afterwards.
How wide is the 1/8" tall ridge? 1-2 ft? You could rent a large flooring belt sander and use low grit paper to sand it down. I did that as well on a significant ridge in our floors, but again, it was under hard wood.

 

[echo4747]

I used tar paper, rosin paper and thinset to fill in dips and taper down abrupt ridges.
I did this under 3/4" oak floors that were nailed in place though.
I'm not sure I would trust tar or rosin paper under laminate flooring since it isn't nailed down. It might feel spongy afterwards.
How wide is the 1/8" tall ridge? 1-2 ft? You could rent a large flooring belt sander and use low grit paper to sand it down. I did that as well on a significant ridge in our floors, but again, it was under hard wood.

I would go with the tar or rosin paper myself

 

[Blanky]

I did one room:

Not particularly happy with it. I used 1-4 layers of felt in the room and then at the far wall where it was off by at least 1/4" I layered some roofing tiles.

One layer of felt is fine (15 lb felt seems about 1/32 thick, 30 lb would be 1/16), but additional layers sound absolutely terrible. They smush when boards are placed on as a test, and I've found many people online complaining of the same with multiple layers of felt.

Going to either replace the thicker parts with 1/4" ply or use the self leveling compound with primer from home depot. My main concern with that stuff is it's going to be a real pain by the walls preventing it from leaking down.

 

[MagnusTheBrewer]

The only sure way is to eliminate the problem with the joists themselves. It's tedious and no guarantees with older homes. Shimming the joists is the slightly easier route. Finally, multiple thinner layers of sub flooring can alleviate problems. Just be sure to offset the thinner layers, use adhesive and, lots of screws.

 

[skyking]

you can sand off 1/16th and re-set nails or re-screw fairly quickly. It will make a big difference in how the floor feels when you walk it.
A belt sander will knock it down quickly.
Speed finish from Custom Building products is the best quick fairing compound I have used; I happily endorse their entire line of grouts and other products as well.
http://www.homedepot.com/p/Custom-Building-Products-SpeedFinish-10-lb-Patching-and-Finishing-Compound-SF10/100152565
It is not a Self Leveling Compound (SLC). You mix it up and trowel it on. It dries extremely fast. Try and get it faired out with the trowel. It sands well but the dust is nasty business.
My house has OSB and some high trusses, and I got through the whole thing fast using a combination of speed finish and the belt sander.

 

[Blanky]

There are some high spots I could sand, but some low, too. It's incumbent I find something to fill low.

The problem with speed finish is that it doesn't work on OSB In fact, virtually no products are rated to work on OSB. Even levelquick, which claims on the package to work only after latex primer, on their website they say to redgard before the latex, then the level quick. There are other feathering products that are also a struggle with OSB. In any case, the floor is likely to flex in ways that will crack this stuff up I think.

There's also no way I am going to ply the whole floor, way too much work

Gonna take a stab at using some of the vinyl I have left over because it's dense and probably not as loud as the felt.

 

[marvdmartian]

You could add about 1/16" by buying some self-stick vinyl tiles (12" x12") and putting them where your low area is. Could even double them up, if they're a smooth, non-textured finish on top. They generally run about $1/tile, at Lowes or Home Depot.

 

[skyking]

I used speed finish on my OSB. I recently pulled some laminate that had been down 6 years to change up some rooms and it was fine. Just my two cents but it was not a problem for me.

 

[Blanky]

Thanks, sky. Most people online recommend the same kind of stuff even though the instructions on these products are not quite being used per specifications. I am suspecting a lot of people just do it anyway and the floor ends up working out okay. I am certainly not ruling it out and prefer something troweled to a leveler for those side wall bits. I mean does it really matter if this stuff cracks into dust underneath the laminate anyway? Possibly not.

 

[skyking]

IF you have excessive flex in the floor then it would not be a good fit for you. I'd look at something more plastic. If the floor is not too flexy, then you'd be good to go with it.

 

[CPA]

The only sure way is to eliminate the problem with the joists themselves. It's tedious and no guarantees with older homes. Shimming the joists is the slightly easier route. Finally, multiple thinner layers of sub flooring can alleviate problems. Just be sure to offset the thinner layers, use adhesive and, lots of screws.

How about using a handheld planer to plane down the peaks?

 

[tsiunltdus]

Make adjustment to the floor joist. Lower the area that is high and raise the lower area if needed using shims.

 

[MagnusTheBrewer]

How about using a handheld planer to plane down the peaks?

Fine for a change of 1/16" but, poor choice for a change of 1/4"

 

[Vdubchaos]

Replace it!

Your life of the floor depends on the subfloor so you are heading in the right direction!

You can also use self leveling concrete....

My sub floor was pretty flexible but I used old school Pergo laminate. The new stuff I see on the market is pure crap (know few people that got it and it's horrible). IT almost seems like companies started skimming out on laminate.

My mom got "industrial" quality done at her business and it's pure garbage...warping all over the place etc.

While my Pergo has been abused beyond believe and still looks like new 10 years later and no warping......weird

 

[Blanky]

Ripping up the subfloor is not happening. I have 1000 square feet, including exterior walls that rest on the subfloor. Redoing all the subfloor would be thousands in labor and I'm positive a professional floorer wouldn't do it if they saw these floors. it's not like an ocean of waviness

I asked some others in my neighborhood who got laminate and the worst I found was somebody with a badly crowned single joist who had to redo it, but otherwise they all threw the floor on and 3/16" tolerance over 10' be damned. The guy at lowes said it was an unreasonable specification and to not bother being so careful, for what it's worth.

I want to clarify above. There is literally not a single product on the market intended to level OSB in the manner I desire. Self-leveler, even with a primer, from all manufacturers, wants a mesh lath put in place and a minimum height. This would be like if you're leveling an entire room, for example, not a low area within a given room. I'm pretty sure a lot of "pros" ignore this requirement and use it to fill low spots on OSB anyway.

The feather finish type product Skyking used is the closest there is, as I think I found one or two (possibly that product) that claim to work on plywood, but again not OSB.

I did find one interesting and extremely expensive product called Dap flexible floor patch. It is a pre-mixed compound that covers 3-4' 1/8" thick for $7 at Lowes. It can be feathered. It's only for plywood and concrete, but I tested some on my exposure 1 rated OSB subfloor and it seems to work. It's also very slightly flexible and says it is a good patcher to fill low spots for vinyl flooring (laminate should work even better then). The manufacturer specifically says not to use on OSB (http://m.lowes.com/pd/DAP-128-oz-Flexible-Floor-Patch-and-Leveler/3011842/qa#!&page=)

As a general rule most patching compounds are not recommended for use on OSB (Oriented Strand Board) as they are often treated with water repellent coatings that can inhibit proper adhesion.

, but it seems to adhere to my OSB quite well, and in any case really I don't need great adhesion; I just need something to sit under the floor and not compress excessively.

The one part of my room that is really low I built up by stapling some 1/8" hardboard and 3/16" ply, then feathered the edges with the Dap. It's drying now.

The rest of the room I'm going to probably do the same thing, or use the cement based featheredge (plywood only, but who cares), or just get to @*#(ing laying floor already like most people do and stop fretting

It's interesting reading so many threads online where people ask this problem and the responses are highly varied. The shingle/felt approach is oft-recommended, but I think only suitable for hardwood that's nailed down and holds the stuff, otherwise it just makes sounds when walked on.

 

[edro]

carpet

 

[Blanky]

carpet

Too squishy; can't lay laminate over carpet.