07-01-2020, 12:31 AM
Whilst it appears to be a moisture problem and the suggestions are relevant (especially if left in primer for a while before the top coats), there could be a more serious reason. If the aluminium was repaired at any time by oxy-welding, it's likely that unless all traces of the flux have been eliminated before painting. it will work it's way to the surface eventually, even though this may take years to appear. Prone to happen quicker in damp conditions, but no problem if welding has been done by MIG or TIG. Good Luck, Cheers, Bill