rusting under clear coat

[bmuss51]

i had thought i finished a new holland hit&miss . which i clear coated the outer ring and flat surface of the flywheel with plasicoat clear from a spray can which looked good. but after it was siting around now for about 3 months after i put the clear on i am showing rust under the clear coat. the material is cast iron on the flywheel which i sanded to get the finish i was wanting. and was very careful not to touch it with my fingers , but i did wipe the surface down with thinner to get the sanding dust off. and let it dry for maybe 15 min. then i sprayed it on my lathe while spinning at a slow rpm. and let the clear dry for a day then resanded lightly with 600 grit. cleaned as before and then recoated again.which when that dried i put the third coat on.but now there is rust starting to show under the clear coat.
the flywheel was powder coated for the main center section. which was heated to at least 400 degrees for that process. so all the moisture should have been dried out of the casting.

if i strip off the clear coat and polish the metal again what can i do to stop this from happening again?

was the problem the brand of clear or what?

 

[rleete]

Spray paint is probably not sealing along the edges. Try a laquer made for clearcoating brass. Heat the part slightly (hair dryer or similar - you want it warm, not hot) and brush or spray on the laquer. Thinning the laquer will help avoid heavy spots. I've used this on polished brass doorknockers, exposed to the elements, and it lasts for years.

 

[Kermit]

The pigments which contain oxygen prevent the formation of rust, while they are in combination with oils, but when the oils either evaporate or become excessively oxidized so that the pigments protrude through the film of oil on the dried painted surface, or in fact loses so much of the oil through exposure that the paint has become porous, it then co-acts with moisture and atmospheric oxygen and the metal surface beneath the paint becomes rapidly and vigorously attacked, whereupon the very pigment which was originally a protective medium becomes a rust producer.

The carbon pigments are elements and consequently can only consist of carbon excepting where there is an impurity or an adulteration present and this is not as a rule premeditated, but rather accidental, at all events they are not generally found to any such a degree as they are in the lead or chemically produced pigments and even when not so the impurities in the former are invariably inert substances and do not promote chemical activity in producing rust.

The carbon pigments show a far superior resistance to the accumulation of rust, when the oils begin to wear out or become eliminated from a painted surface after prolonged exposure than do the oxygen pigments, moreover they are not affected to any extent by acids whether in the liquid or gaseous form. Hence, it will be seen that the carbon pigments are to be preferred, graphite especially, for graphite which is also used as a lubricant possesses such a degree of fineness of texture that it gives the paint where it is used as a pigment, such a slippery surface when several years dry, that it reduces to the minimum the abrasive effect of water, snow, ice or mechanical abrasion, etc.

Just one possibility,
Kermit