Sealant / Primer for OSB

[That would work]

I guess any exterior paint of you colour choice then.... even fence preservative?
Condensation between the sheets and the board may be an issue to manage though.

 

[xtian170174]

I guess any exterior paint of you colour choice then.... even fence preservative?
Condensation between the sheets and the board may be an issue to manage though.

That's the clincher really - I'm reading that a paint is technically more a plastic once it's dried - then surmising I shouldn't worry about it so much, and obviously nearly every product out there could be wiped clean enough to eat off, so if everything went well it would seem like a clinically applied measure of each layer going down without issue and the PC sheets only against a cured surface with no reaction possible - but condensation presents some microscopic level of problems arising, moisture being held against two material/substances could trigger something in the long term, possibly foreshortening an expected 15-25 year problem free roofing job to 5/< years. IDK.
English Winter & Summer are not to be trifled with no matter how clement people say it is compared to other parts of the world, the temperature variance addles as easily as anywhere else, but adding moisture to that serves only to expedite it.

 

[That would work]

So long as the osb is 'cold' ie if there is insulation underneath it there should not be an opportunity for condensation to form between the boards and the PC.

 

[xtian170174]

So long as the osb is 'cold' ie if there is insulation underneath it there should not be an opportunity for condensation to form between the boards and the PC.

Agreed and this too is on the cards - the original '80mm rigid foam composite' would have been an all-in-one product to that end, so I'll be fitting something to achieve the same insulation, the OSB and PC combined will give a thickness of 34mm - an intended thicker 35mm multiwall PC roof light may present a problem here as it will quickly take on heat - it's area is about 4x1.5m, might have to forsake that idea...

 

[lexi]

Your OSB is already impregnated in glue? You could use one of the cheap Zinc Phosphate paints from Regal Paints. I have found the one for steel is excellent on wood as an all round paint.

 

[Kevin mc veigh]

[i.e. multiwall polycarbonate - there are solid sheets, but these are not being considered]

Use black fencing paint /stain

 

[xtian170174]

Thank you everyone for all the help and insight so far.

Looking into this, it seems polycarbonate is a bit of a wimp, but some of its properties are so desirable that it has earned & deserves its place in proper uncompromised [conventional] use.

What I am going to do, & I think if you look into this too that you may agree, but I welcome all feedback - is to use KA's SBR latex primer to treat the OSB and then - new material; apply 1mm thickness of copolymer polypropylene which can be overlapped where necessary and still closely clamped down on to with the final layer of PC.
The PP sheets are much more tolerant of chemicals and as a solid black colour also negates the need for a coloured [bituminous] paint/epoxy resin coating, I do not foresee an issue with this, the respective stabilities of PP & PC aren't affected by being adjacent and the barrier PP provides means I could go further with the OSB treatment, but will [hopefully] not need to....

 

[OldWood]

Xtian - I take it for reasons I can't immediately see, that you haven't considered Coroline or Onduline. Absolutely no bother to install, very long lasting and lays onto OSB without any further protection.

Rob

 

[xtian170174]

Xtian - I take it for reasons I can't immediately see, that you haven't considered Coroline or Onduline. Absolutely no bother to install, very long lasting and lays onto OSB without any further protection.

Rob

Thanks, worth expanding upon - I haven't been looking into corrugated materials, I've viewed them, but not regarding them in this context as any added insulation may have cavities, or as you describe the OSB backed on to them would have - I only really conceive of both a plastic inner & outer wall of a cavity as an inhospitable environment where problems are much less likely to occur - and the original box profile direction of the project was the only sort of product that is manufactured completely filled inside the corrugations.