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Old 10-25-2021, 07:51 PM   #1
Mini-Skoolie
 
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Was OSB subfloor the wrong choice?

Hey guys, this last weekend i went to lowes and got 3/4" OSB T&G for all my subfloor but later i got to thinking that maybe this wasn't the best choice? This subfloor will be going over 1" XPS R5 rigid foamboard (without being framed). I plan lay vinyl flooring over the subfloor. Will OSB be sufficient considering my circumstances? Or do i need sheathing? I guess my main concern is water/moisture and the porousness of OSB. There's quite a big price difference between osb and plywood.

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Old 10-25-2021, 08:03 PM   #2
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You should be ok with 3/4" T&G. Is it a subfloor material, I would suspect so at that thickness and T&G. It helps that it's not on the metal floor. I would not use regular OSB in a bus.
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Old 10-25-2021, 08:43 PM   #3
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You should be ok with 3/4" T&G. Is it a subfloor material, I would suspect so at that thickness and T&G. It helps that it's not on the metal floor. I would not use regular OSB in a bus.
Ok thank you, and yes it is subfloor grade. Here is the OSB i bought...https://www.lowes.com/pd/23-32-CAT-P...x-8/1000065715
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Old 10-25-2021, 10:07 PM   #4
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The main difference between plywood and OSB is that if plywood gets wet and is allowed to dry out thoroughly (before rotting can occur), it will be nearly as good as new. If OSB gets wet, even if it dries out thoroughly it will be permanently in worse shape than before - weaker and more difficult to dry out if it gets wet again. If you've sealed your bus up well and don't have water leaking into the interior, your OSB floor will be fine.
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Old 10-25-2021, 11:10 PM   #5
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The main difference between plywood and OSB is that if plywood gets wet and is allowed to dry out thoroughly (before rotting can occur), it will be nearly as good as new. If OSB gets wet, even if it dries out thoroughly it will be permanently in worse shape than before - weaker and more difficult to dry out if it gets wet again. If you've sealed your bus up well and don't have water leaking into the interior, your OSB floor will be fine.
I would avoid OSB for this reason. The likelihood of a leak in a bus over time is high, and it would be a shame to have a bubbled up section of floor because of it.

Plywood holds up better and doesn't swell or deform with the first moisture.
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Old 10-26-2021, 10:41 AM   #6
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The material she chose has sealed edges for water protection, unlike regular OSB.
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Old 10-26-2021, 12:54 PM   #7
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What I used

Also used osb water resistant sub floor over XPS 2" foam and I've briefly flooded my bus 3 times with no noticeable effects. Drained the bus on a slope and dried it out thoroughly each time with fans and heat. The plank flooring shows no sign of problems and the walls are A-ok.


I used some left over redguard paint on the OSB flooring in the bathroom and under my bed where the water storage tanks are.


https://www.lowes.com/pd/AdvanTech-F...4-x-8/50126556
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Old 11-11-2021, 01:49 AM   #8
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If you are concerned about moisture deterioration, paint it.
.
Dab paint into all the nooks and crannies on all surfaces.
Dry it a few weeks, then paint it again.
.
.
In a well-insulated structure with limited air-exchange, humidity ends-up someplace.
If you are concerned about moisture accumulating in your sub-floor, you could add ventilation... or use those channels to distribute treated air from your heater and air-conditioner.
The idea -- move the air instead of stagnation.
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Old 11-11-2021, 09:34 AM   #9
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I even painted my 15/32" plywood subfloor with a couple coats of Kilz, on both sides and edges... because water leaks have been a chronic issue in my bus. I also removed and resealed half of my windows this fall, and I'll do the other half next spring, as soon as it warms up enough for the polulyeurethane caulk to be workable again.



Today I'm sanding (free!) beetle kill pine planks, because hopefully this weekend will be warm enough to stain them. So perhaps my floor will be installed by Christmas. ;)
(Which wouldn't be so bad if I weren't still living in my bus full time during the whole remodel project.)
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Old 11-11-2021, 09:39 AM   #10
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if the bus isnt yet built id rip that OSB out and put Only marine grade plywood down.. ive seen marine grade plywood last decades in busses.. in fact many old GMC city busses have marine grade plywood EXPOSED to the elements on the underside of the bus and have lasted amazingly well.. I see OSB come apart on houses after a couple short months of water getting behind vinyl siding
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Old 11-11-2021, 04:05 PM   #11
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if the bus isnt yet built id rip that OSB out and put Only marine grade plywood down.. ive seen marine grade plywood last decades in busses.. in fact many old GMC city busses have marine grade plywood EXPOSED to the elements on the underside of the bus and have lasted amazingly well.. I see OSB come apart on houses after a couple short months of water getting behind vinyl siding
The T&G 3/4 flooring OSB is different than the 1/2" crap used for siding.
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Old 11-11-2021, 04:11 PM   #12
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it may be better but if it isnt marine grade it shouldnt even be on the floor of a bus.. i dont care how much you seal up a bus when you build it.. the game is all different caught in a torrential rain at 60+ MPH.. people put lots of work into some really awesome builds.. how bad would it suck to have to pull all that apart because you save a dollar or 2 on plywood then have water get in and start molding in the OSB
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