We are planning a reno in the next 5 years that will more than likely involve removal/replacement of the existing skillion roof. So time is exactly what we need to…

Thanks for the suggestion. But what about treating the rust? Surely that needs to be treated first to prevent the rust from getting worse underneath the rubber membrane.

So I'm restoring our 40yo galvanised flat roof. 80% surface rust, no serious damage.
Mostly surface rust surrounded by patches of original gal on the unrusted areas. So a combination of…