Hi All,

I'm new to the forum and been reading all the great advise and techniques posted here.

A friend of mine hired Denver Hardwoods to install a 2000+ sqft padded, maple floor over concrete subfloor in dance studio. The floor looked like a mirror when completed.

I'm in need of some help. I'd like to get the same kind of flatness on a 600sqft floor with an OSB subfloor, using 3/4, 5 inch stapled oak. Also I cannot afford to spend $12K on a floor, so I'm doing it myself.

Details:

The house is a '90s spec home, not built to exacting standards or any standards for that matter. How it passed inspection is a question many contractors have asked.

The floor is not particularly flat. The OSB rises on the edges, I'm assuming it got wet during construction. Some joists are 1/4 inch low/high I can't tell what to use as a reference. It looks like the rough-in crew was drinking too many beers.

Options I can think of:

1) Rip out the OSB for advantec subfloor. I don't want to, the boss (my wife) won't go for it.

2) Lay another subfloor over the existing, it will not get rid of the 10ft long wave caused by the joists and there will be height problem with the other oak floors.

3) Sand and shim. I can sand down the high edges, but it doesn't fix the goofy wave.

4) Sanding edges and self leveling compound. From what I've read, self leveling is not really "self-leveling" plus some articles here and other places say it cannot be nailed/stapled without cracking and causing future creaking problems.

What other alternative and best methods do I have ?

Suggestions appreciated.

BTW, I'm thinking about using fiber glass resin with a slow cure agent as a self leveling compound. I've used it on ship's decks. It sticks to everything and it does not crack when nailed.

thanks
-gary

Start by sanding the edges of the sheets after the nails are set. It should have glue between the sheets and floor joists, but add nails if there are squeaks.
After the high spots are sanded at the edges you may be able to sand some of the hump and then build up the low side with thick roll roofing. I would not recommend more than two layers of roll roofing, but if more thickness is needed then you can then put three-eighths plywood, then step up to one-half inch, and so on. Glue the plywood down as you go and staple or screw or nail along with the glue. Glue in a caulking gun will be most convenient. You can use tarpaper under the plywood to help step the fill gluing the tarpaper with latex sub-floor adhesive then plywood to the tarpaper. I have filled a low spot with an inch and five-eighths of layers to fill the slope of a porch that was enclosed. I hope that the low part of the"wave" is not right next to another floor that you want to match the height.
It's slow going. Use 16 grit paper and a floor edger to start.

Thanks Pete, The sanding will be brutal. I'm not sure if the edge sander or a 3hp orbital will work better (have the orbital). Tomorrow, I'm going to experiment with the fiber glass resin. The bondo guys gave me a few 1 pint cans. The gallon cans are not much more cost than the self-leveling compound. I'm not sure how much a gallon can will cover, bondo has a habit of only filling cans 3/4 full. And I think resin will be much quicker than tar paper. l am concerned about the resin out gassing something very bad. (ala LL).

An edger has a one horsepower motor and with a 7 inch disc you can really create some saw dust using a 16 grit paper. The edger can concentrate the grinding right where it is needed and you feather out as it gets flat.
The orbital sander will not be the best to sand the edges of the sheets, even if you can heel it in to concentrate the force.
I use tarpaper because it works and is less expensive and faster to use than anything that you need to mix. Some mechanics use three tab roofing. You only need to be within an eighth of an inch to be within the guidelines of a flat floor for most flooring specifications. Each layer is close to an eighth inch thick, so just mark the floor with a crayon like a topographic map, using a straight-edge and see how many layers you require to get close to exactly flat.

[Sanding high edges]
Pete, You were absolutely correct about the orbital sander, it doesn't cut. I tried the orbital yesterday, no way will it work to be done in this century. I "need" a flooring edge sander.

The topo map is a great way to fix it, but due to the way the light hits the floor over a 25 ft length, even slight waves are very noticeable.

[Self-leveling experiment]

I tried a bit of an experiment using bondo's 404 fiberglass resin over a 2x3 ft x 1/4" simulated warped floor. The stuff has a higher viscosity ( thick honey) than I think would work to truly self-level for the curing time. Having said that, it flows much, much better than other self-leveling compounds. The bondo also seems to shrink about 5%, or at least is appears that way to me. I'm calling them tomorrow to confirm and if it continues over time. Bondo resin definitely does not crack off when nailed and stapled like Henry 555.

Here is a problem with bondo, it a polyester resin which smells bad for along time and not truly designed for interior applications, indicating it could be toxic.

The alternative to polyester resin are polyurethane epoxies, commonly used used self leveling counter top finishes and casting molded parts. It is definitely less noxious than bondo, shrinks 1%-3%, however it is more expense by 20% and the counter top formulations take much longer to cure (8hrs min).

I'm going to order a polyurethane epoxy, as soon as a I figure out which type to order. My objective is finding one that will truly self-level (before curing), cure within 2 hrs (walk on), can be applied to OSB and advantech subfloor without separating and no special prep, won't chip when nailed and stapled, and won't be too hard that interferes with pneumatic stapling/nailing.

How much resin ? I calculated 3.2 gallons to cover the 500 sqft with 1/8" average thickness. Should I be worried about the extra $60 for polyurethane? NO!

Stapling or nailing through the coating as long as it is not too thick will not be a problem. Epoxy coatings aren't really that hard and as long as the fasteners penetrate ¾" into the sub-floor you will be good.

I have leveled the floor using about 5 gallons of polyurethane epoxy. It is dead level. Poly flows like water.. The big issue was sealing every little crack After a day of curing, it is fully hardened and stuck to the osb like glue. Its not ever coming off. After a few days there is no noticeable smell.

The drawback is cost and getting this stuff spread out. The wet poly is VERY slippery. I used an old set on cramp-ons to walk on the floor.