osb outside in damp

[steveo3002]

in the summer i re did my shed roof with 3/4 osb and epdm sheet , i have a 2" or so overhang with the underside exposed to the air/damp and seem to get a bit of splash back from the gutter

i was led to belive osb is the stuff for the job , but i left a few offcuts laying around they gone all swollen and crumbly from the rain

so is it going to fail being exposed on the underside to the damp english winters , i will get up there and paint it with some gloss once the spring is here

 

[Jan]

If I were you I would wait to see if we get a Summer this year. If the material is as damp as I suspect then it could take many weeks for all traces of the water to evaporate. Although it could slowly migrate to other parts of the sheeting and evaporate from there the existence of damp under the paint could easily compromise its adhesion.

 

[MattF]

so it going to fail being exposed on the underside to the damp english winters , i will get up there and paint it with some gloss once the spring is here

Is this a question or a statement? Whomever suggested to you that OSB would stand upto the elements was a plonk. It's little better than standard chipboard in that regard.

 

[steviec_lj]

Any "cut" wood left out to the elements is going to swell and crumble without a protective coat of something.

Its a bit like leaving a length of mild steel unprotected outside and being shocked that after time it will rust.

 

[awemawson]

There are three grades of OSB. #1 & #2 are for dry conditions, #3 is intended for potentially damp conditions. I think the difference is only the glue used to bond them, and as has been said, the particles of wood that they are made from will swell.

Andrew

 

[steviec_lj]

Yes, OSB3 is polycoated, but I believe you still need to use a suitably waterproof preservative treatment.

 

[steveo3002]

right ive been down the builders mechant and theyre telling me they only do osb3 in that size so hopefully it should hold up

theres one bit im not happy with , water seems to somehow splash back /blow maybe ? and wet the underside of the overhang that drips in the gutter

can anyone think of something like hardboard that would stand up to water splashes and cheap /easy to cut as i think i will panel it to keep the wet off the osb

 

[Fintray]

What about a roll of DPC that would be cheap, flexible and waterproof!

 

[steveo3002]

hmmm yeah the price is right on dpc...never handled any is it flexible enough ?

 

[Shedendman]

you should really dress the felt or covering back underneath the overhang and let it trail into the gutter,OSB is a sod when the edges are wet no matter what grade soaks water up like a sponge if you can and it'll need to be very dry a good plastering with horrid black sticky bitumen paint will give a better protection

 

[steveo3002]

edges are covered ..its just the underside thats exposed

i have previously ran the felt around the underside and found the water would just follow around and not want to drip off

 

[bigegg]

+1 for the bitumen paint - or car underseal - the wet will wick around hardboard and it will just rot out anyway.

 

[rikrobson]

The best stuff to use is creosote mixed with old engine oil. Just a wee bit too nasty these days, but no water gets in and nothing grows on it. the trouble you are going to have with the water getting in to the osb is mould spores and the fibres will stay open once dried allowing the moisture in to the board at the next damp period. Mind you its always damp up here.

 

[brightspark]

The best stuff to use is creosote mixed with old engine oil. Just a wee bit too nasty these days, but no water gets in and nothing grows on it. the trouble you are going to have with the water getting in to the osb is mould spores and the fibres will stay open once dried allowing the moisture in to the board at the next damp period. Mind you its always damp up here.

i paint all my fences with genuine coal tar creosote a bit of parafin and a cup full of waste engine oil and the fence is 30 years old . ****** to people that say its banned