Sealing sawed edges of OSB

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Old 11-28-20, 10:47 AM
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Sealing sawed edges of OSB

I'm on a birdhouse building campaign using scraps of OSB siding. In past experiences, it appears the sawed edges gradually delaminate in time/weather, even when painted. What would be a good product to seal the porosity of them prior to painting?
 
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Old 11-28-20, 12:08 PM
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Maybe Minwax wood hardener. It's basically a liquid plastic resin. OSB is just not a very good material for exterior use... painted or not.
 
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Old 11-28-20, 01:11 PM
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Yea, OSB is never supposed to be exposed, always covered by siding or roofing. Probably not a question of if, but when it will fail.

Regular old plywood would be an easier material to work with!
 
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Old 11-28-20, 01:19 PM
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Even cheap pine would be better then OSB.
Make them out of Cedar and there's no finishing needed.
 
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Old 11-28-20, 02:57 PM
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Yea, OSB and moisture of any type just don't mix. I have had some luck sealing OSB with oil based paint or polyurethane. I suppose water based would work but I've never tried it. Paint all surfaces, especially the edges. Then let it dry for a day or two. Then paint on another coat. Keep repeating until you can see that you've filled all the crevices and pinholes.

Doing it all in one coat doesn't work as the paint just keeps soaking in. You need to put a layer on and let it dry so it starts sealing up all the passages and nooks & crannies.
 
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Old 12-01-20, 09:15 AM
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Thanks for all the replies. I'm using either exterior OSB siding or facia board that is prefinished with embossed wood grain sealed surface, not raw OSB. It's used as siding on buildings and it lasts for decades with normal maintenance. The only problems ever exhibited are where exposed edges or bottom drip edges haven't been protected--same as I want to avoid with the birdhouses. I've used paintable silicone caulk on some that have been out for a number of years but eventually, the caulk tends to peal and lose its seal. That's why the request for alternatives.
 
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Old 12-01-20, 03:06 PM
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Your talking about LP Smartside.
 
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Old 12-02-20, 03:04 AM
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While caulking is good for filling the pores/edges it will last longer if it's painted.
 
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Old 12-02-20, 07:04 AM
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I'm assuming your using Exterior or Exposure 1 grade material. This material is coated which is why it will resist water, but if your using scraps with cut edges that is when the protection does not exist as you have noted.
 
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Old 12-02-20, 08:46 AM
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Try dipping the edges in paint and let it soak in. You also try dipping the edges in melted paraffin but paint will probably not stick to that. Maybe paint first then paraffin?
 
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Old 12-02-20, 12:10 PM
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I would skip the paraffin as paint won't adhere to wax long term. Wax over the paint could complicate repainting later.
 
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Old 12-02-20, 04:29 PM
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You could try this... https://www.rustoleum.com/product-ca...ife-coppercoat

Home Depot should have it. And you can paint over it. If you have cut edges you should sand them smooth first before treating them or priming them. On most LP siding, its the fuzzy edges of the cut that soak up water first.
 
 

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