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OSB for bathroom


1sthouseSLC's Avatar
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05-18-14, 07:38 PM   #1  
OSB for bathroom

I got two full sheets of 3/4 inch OSB for free today and I'm wondering if I can use it under 1/4 inch cement board with tile over that? I could use it other places, but I would really like to get further in the bathroom I started remodeling 3 years ago!

 
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05-18-14, 08:03 PM   #2  
In my opinion the answer is no. I would never use anything but genuine exterior-grade underlayment plywood in an area where the floor might get wet.

Others may have different opinions.

 
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05-18-14, 08:36 PM   #3  
If the neighbor drives his car through your bathroom wall you can definitely use it to temporarily patch the hole but that is the only time I would use OSB in a bathroom. Some would argue well they use it for roof decking and I would reply ever seen OSB after water got under the shingles? I have. I could put my fist right through the mush that was left.


I can explain it to you, but I can't understand it for you.

 
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05-19-14, 03:58 AM   #4  
Unless I'm mistaken, most 3/4" OSB is treated with some type of waterproofing so it won't be damaged by the weather during construction .... but I agree - plywood would be better! Another thing to consider is the size of the joists and how far they span, sometimes you need an additional layer of plywood to stiffen up the floor.


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05-19-14, 06:45 AM   #5  
Would it be enough for a normal subfloor, ie not a bathroom? What distance between joists should be stiffened with plywood? I think the joists are 16 inches apart, but it's been awhile since I measured.

 
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05-19-14, 08:47 AM   #6  
16" centers is the norm but the joists size and how far it spans between supports is what you need to pay attention to. A tile floor needs to be stout with no flexing so the tile/grout won't crack. Other types of floor covering are more forgiving.


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05-19-14, 10:34 AM   #7  
Your OSB will have an APA stamp on the back side that tells what it's rated for, but since your joists are 16" OC that's nothing you even need to worry about.

While plywood is certainly better than OSB in wet areas or areas that may potentially get wet, there are hundreds of thousands of houses that have been built entirely with OSB as the subfloor, wall sheathing and roof sheathing. Plus since yours will be covered with cement board I would use it and not lose a bit of sleep over it.

I will say that for a floor, it would be better to use tongue and groove OSB rather than just plain old square edge 3/4" OSB. But read your APA stamp and tell us what it says.

If you say you can use the OSB other places, why not go buy some t&g plywood and be done with it?

 
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05-19-14, 11:02 AM   #8  
<Opinion>
there are hundreds of thousands of houses that have been built entirely with OSB
And probably that many built with hardboard siding and look what the courts finally said about that.</opinion>


I can explain it to you, but I can't understand it for you.

 
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05-19-14, 11:11 AM   #9  
While I agree that the old masonite siding wasn't a great product, the failures could almost always be linked back to improper painting or installation. It must be oil primed and the paint kept in decent shape, all protrusions into the siding must be filled/sealed. As long as the siding itself never gets wet - it will last a long time. I used to work for a big painting outfit and I happened to be at the office one day and the boss lady said she was glad they didn't use any masonite on the jobs I ran. She was shocked when I told her all the siding my builder used was masonite BUT he never installed it close to the ground and I made sure it was prepped and painted right. No siding failures over a 10 yr period.

I agree with X, plywood would be better but I wouldn't be scared of OSB.


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05-19-14, 12:08 PM   #10  
Guess I forgot to mention that it is tongue and groove osb. I'm not at home to look at the stamp, but I will when I get home.

As much as I would love to buy plywood, and I will likely wait until I can, I wanted to use this in the bathroom as it has been torn up 3 years now. Classic story of buy cheap fixer upper, then start having kids before it's done. Now I'm the only one working supporting 4.

 
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05-19-14, 12:28 PM   #11  
Don't let my old school attitude discourage you from doing what others say is correct.


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05-19-14, 01:15 PM   #12  
Unless your kids regularly flood the tile floor I don't think moisture is likely to reach the OSB. If you were to have an unnoticed plumbing leak, I'm not sure a better subfloor would help a lot.


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05-19-14, 03:06 PM   #13  
The house I bought for my sister supposedly had a plumbing leak that caused all sorts of problems I won't go into here. My personal opinion is that the washing machine (laundry room on second floor, back-to-back with the bathroom) either overflowed, the drain hose popped out of the drain pipe or a water hose leaked severely or possibly the toilet upchucked. I came to this conclusion because there were no obvious repairs on the plumbing which was all exposed and there were no leaks in the fixed plumbing. The toilets, however, were a make and model that was prone to plugging.

Anyway, the flooring was ruined and removed in the laundry room showing the OSB sub-floor. That floor, although it was "sealed" by the mold abatement company, was swollen and warped severely. I ended up cutting out about half of the floor, back to a point where the OSB was sound, and replacing it with 3/4 inch exterior plywood. Some of the removed OSB had swollen to almost an inch of thickness. The plywood sub-floor in the downstairs area that had gotten wet suffered no problems other than a sparse amount of mold.

 
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05-19-14, 04:42 PM   #14  
Ray, though it will cost more and extend the fix up time, I would much rather do it right than just use what I have because I have it. While we do not plan on spending more than a few more years here, I have no desire to leave others with anything but a quality remodeled home. In short, I value everyone's opinion.

I looked at the stamp and it says it's exterior grade sheathing. I don't know if this is all the needed info, but I still plan on using this in "dry" locations.

 
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05-19-14, 05:24 PM   #15  
As with t&g plywood, if you do use the 3/4" t&g OSB on a floor someday, place the long axis of the plywood perpendicular to the floor joists. That way the t&g is supposed to lock together between the joists.

 
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