HOW LONG WILL THE EXAM PAPER LAST BEFORE IT DETERIORATES ON THE PLANE WITH DOPE OR WHAT EVER PAINT IS USED...
My own experience trying a couple different 'doctor papers' is maybe one to three years, after which it becomes so brittle that even the lightest finger pressure results in a puncture or split. Those I've seen have no fiber content (like cloth fibers or weave), just scattered matt paper fibers. The old silkspan had a grain direction to it which indicated how the strengthening fibers were oriented. I don't know for sure but those fibers could have been silk fibers-hence the name.
I mentioned earlier elsewhere that other than finding some old stock real silkspan the stuff our friend Dave Rigotti provides ( don't know what it is exactly but you can visibly see a fine woven mesh inside it to which paper fibers are attached) is the best I'm aware of. It hasn't been around for us very long so I can't speak about longevity yet but I'm more confident in it than anything else. Real silk is still an option and there are some on-line suppliers with a lot of selection and very fair prices. Thai Silk comes to mind. Dope never stops shrinking. I've seen doped silkspan pull and squeeze an airframe to the point of crushing soft ribs inside over time. The doctor paper simply won't hold up to it very long.
Dave