Sealing & finishing OSB

Finishes, paints and coatings

Sealing & finishing OSB

Postby Vajra » Wed Mar 09, 2016 10:14 pm

I recently picked up a very cheap and large trailer. I thought it would be great for a slightly larger and odder than normal teardrop. I would like to keep costs down if I go that route of teardrop, having looked at build methods and materials, I think OSB wouldn't be bad for exterior giving the fact that the stick frame will be thicker than normal, for extra insulation. I know it won't be long before the plywood vs OSB argument gets brought up not interested in that. :roll: It has far less voids than plywood, It is very strong and cheaper long run. My question is what would be the best way to seal it and finish it. I have seen some finished OSB floors, cabinets, that looks very interesting. I wish I could get the wood to look more like old grey barn wood, but I don't think that is a option or all that possible. Maybe with spray paint in a light coating. But after that, how would one go about sealing it or will it not take sealing very well? Would layers of clear varnish, polyurethane or epoxy work? Can I treat the wood as if it was a normal plywood exterior? I am not planning on edge moldings or trim, unless it would be to cover panel edges. I don't like the idea of having a painted surface unless it is the best way to preserve the wood and seal it. Where I am, once in a great while we get small hail, and sleet. This will be outside 24/7. I might cover it during winter. Winter -10F at most, summer 110F at most. Fair amount of rain in Michigan, so I do think moisture will be a issue needed to address along with the other elements. Is there a good way to effectively, protecting the natural look of the wood, sealing it from the elements that will last? Can this also be used over the surface is painted? Thank you in advance, especially if you have done it with lasting results! - Vajra
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Re: Sealing & finishing OSB

Postby Andrew Herrick » Tue Sep 20, 2016 5:29 pm

How you finish OSB depends on its internal adhesive. If you use AdvanTech, for instance, which uses an epoxy resin, you can stain it or varnish it - but you can't use any sort of latex- or water-based primer or stain. You'll have to read the manufacturer's installation instructions.

In general, you can stain OSB with an oil-based interior or exterior stain. You can also apply a polyacrylic, polyurethane, or spar urethane finish. Spar urethane might last longer since the OSB will change size with temperature. So long as you don't mix incompatible materials (see above paragraph), it could work. If you're going this route, using a solid or semi-solid exterior oil-based stain and coat with 4-5 coats of spar urethane. You'll need the UV and moisture resistance. Transparent stains are pretty, I know, but the more transparent the stain, the less the wood is protected. It won't last 30 years, for sure, but it'll work.

Most OSB's respond better to oil-based primers and stains. Several "exterior" OSB's also have a wax coating which can interfere with adhesion.

The problem isn't chemical compatibility. It's durability. Even the best OSB panels are rated Exposure 1, and NOT Exterior, and certainly not marine. On a cheap floor? No big deal. But they also epoxy or literally POUR polyurethane onto the OSB to give it that sleek, shiny look.

Anyone ever try using aniline dye on OSB??? Wonder how that would work ...

Painting the OSB technically gives superior moisture and UV resistance, but it comes with another problem: telegraphing. OSB doesn't sand well, so you'll have to sand, sand, then prime, prime, and then paint, paint and paint. OSB sucks up paint like crazy. Some people use masonry "block filler" to fill it out to get a smooth surface.

Something else to consider: If you drill through the OSB, you'll have to waterproof all your fastener holes with rubber washers or bed your fasteners with silicone or some such. Else water will wick into the holes and get behind your protected surface and rot the OSB from the inside out.

You can clear-coat epoxy OSB, yes, but that cuts into the "cheap" part of it ...

Really, it's a question of your time. Can you get an OSB exterior to work? Yeah, you can. But it'll be a 7-step process before you're through. If you want the special look of finished OSB - which some people love - then it's totally worth it. Some people have even built OSB boats. But if you're just looking to save money ... :thinking: Well, if you like the look of old gray barn wood, why not use it? Lots of people will let you haul off their scrap wood for free. Just a thought! :)
Last edited by Andrew Herrick on Tue Sep 20, 2016 10:14 pm, edited 2 times in total.
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Re: Sealing & finishing OSB

Postby Padilen » Tue Sep 20, 2016 6:37 pm

My mother's Tow Lite had OSB floor from factory!
I built a shed and used OSB as siding in 1987. After 15-20 years the bottom 1-2 feet had absorbed moisture . I marked it at 2' and cut all the way around. Replaced it and replaced the doors. My friends( tandempair) bought it and still have it today.
But if I was to do it over( wont) I don't think it would be my first choice. I also read a thread about T11 1 it's not really any better than OSB but paint and stain friendlier. It could be just my climate, and crawly critters & critters. Nothing last !


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Re: Sealing & finishing OSB

Postby Padilen » Tue Sep 20, 2016 6:41 pm

Padilen wrote:My mother's Tow Lite had OSB floor from factory.
I built a shed and used OSB as siding in 1987. I used quality paint and caulked everywhere. After 15-20 years the bottom 1-2 feet had absorbed moisture . I marked it at 2' and cut all the way around. Replaced it and replaced the doors. My friends( tandempair) bought it and still have it today.
But if I was to do it over( wont) I don't think it would be my first choice. I also read a thread about T11 1 it's not really any better than OSB but paint and stain friendlier. It could be just my climate, and crawly critters & critters. Nothing last !


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