OSB as carpet underlayment?

Hi, I had specified new "underlayment" to be put over the old 3/4" pine board subfloor in a new 2nd story addition. What our contractors installed in our absence is regular 1/2" OSB sheathing material, not specifically rated as underlayment. They screwed and glued it down very well. After two weeks I already see swollen areas and chips coming loose due to water being dragged in and left due to the construction. Is OSB sheathing considered a reasonable underlayment for a carpet? I expected plywood rated underlayment, with the top side sanded, not this chunky stuff which is not even particularly smooth to begin with. Regards, Wolfgang in VT
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snipped-for-privacy@gmx.net wrote:

Hi, They do use OSB but never in my house. My idea of OSB is only for vertical plane. Tony
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water is no friend to plywood either.
to save things maybe complete drying with additional fans, Bin primer to seal the floor, top coats of paint that matches the primer type, and a thicker carpet pad.
what you bought for the job may vary: there are different finishes on the OSB according to this quoted website. "Special Features of OSB and Waferboard Panels Panels 15.5mm (5/8") and thicker are manufactured either with a square-edge or tongue and groove on the long edges. Panels may be sanded smooth on one or both sides for particular end uses such as floor underlayment or interior finish, or they may be spot sanded to meet the required thickness tolerances. Manufacturers may alter the surface of some of their OSB or waferboard panels to make them more suitable for a particular end-use." it says at: http://www.cwc.ca/products/osb/uses.php
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Thanks for the replies. I will talk to the contractor tomorrow. What they put down in my house is regular "APA rated sheathing", not sanded, no tongue and groove. I specifically excluded OSB from all other areas of construction (wall and roof sheathing, bathroom subfloor), but did not do this for the carpet underlayment since I had never even seen OSB rated "underlayment", so am a little frustrated that they went cheap on me there. Just tells me that one should never "assume" anything in a contract... Regards, Wolfgang
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On 14 Jan 2006 21:26:59 -0800, snipped-for-privacy@gmx.net scribbled this interesting note:

I wouldn't recommend 7/16" OSB for flooring. Any moisture for any length of time will cause it to swell.
Plywood can last a long, long time. I just worked on a floor that has 5/8" plywood sheathing. Based on the design of the kitchen, I estimate it is the original flooring material which means it is about fifty years old. Most of this floor was in good shape and only a small amount needed to be replaced, despite years of moisture (what with it being in a kitchen and having those 12" vinyl tiles on it.) In similar circumstances, OSB would have failed completely in a very short period of time.
Your remedy? It wouldn't be too expensive to laminate (glue and screw) 1/4" plywood on top of that OSB. That would be far easier than trying to tear out all that OSB and install new plywood.
I'm sure OSB is fine for some applications. I'm not sure what they are, but I'm sure there is something it is good for. I know many here think OSB is a fine material, and this has been discussed many times, but the only real reason to use OSB is to save a little money up front, although, in my considered opinion, it will likely cost you more in the long run...
-- John Willis snipped-for-privacy@airmail.net (Remove the Primes before e-mailing me)
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snipped-for-privacy@gmx.net says...

If it is a '*new* 2nd story addition' how can there be anything *old* in the *new* addition? :-)

'Underlayment' is an ambiguous term. I have seen; 1/4" luan plywood, 7/16" OSB, 1 1/2" light weight concrete, 2 x 6 T&G SYP, 3/4" T&G exposure I plywood, and ... 'underlayment'.
Underlayment and sheathing refer to the use of a material not the type/size/physical-properties of a material.

Millions of yards of carpet have been laid directly on OSB.

Expected or specified?
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Hi Mike, The second story is new. The subfloor however was preexisting in the former attic, since we did not change the footprint of the space, only the ceiling height... I specified "underlayment suitable for carpet application" in the contract. What I found so far is that APA does not recommend "rated sheathing" material as underlayment for any floor, only "Sturd-I-Floor" OSB is recommended for carpeting. But I am not saying that what we have now won't work, just wanted to educate myself before talking to the business owner. Do you know if the OSB you have seen is the "sturd-i-floor" stuff? Thanks for your input. Wolfgang
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snipped-for-privacy@gmx.net says...

Per the APA website, OSB APA Rated Sturd-I-Floor is an OSB panel intended for *single-layer* flooring.
"underlayment suitable for carpet application" does not require/equal 'OSB APA Rated Sturd-I-Floor'.

Some of the OSB I have seen is APA Rated 'Sturd-I-Floor', most was not.
APA Rated Stud-I-Floor is an OSB panel designed for a specific use. OSB Rated Sheathing is more than strong enough when used as carpet underlayment because the strength of the floor is in the subfloor.
I think the real issues are .... Does the underlayment need to be repaired or replaced? Which specific locations need to be repaired or replaced. Who pays for the repair/replacement. Was the subfloor adequate?
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Thanks to Mike and all for the replies. We'll just have to see how it holds up over time. It would not have been my choice to save 100 bucks or less in material (we are talking 240 square feet here) over proper plywood, but it does not seem to make sense to rip it out at this point. Regards, Wolfgang in VT
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Dry it completely then coat with outdoor polyurethane to make it water resistant if you suspect it will get wet again
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