Fixing rusted pitts in sheet metal

Another method I have used on very badly pitted metal is to spray the self etching primer on as usual and let it dry. Then mix up a small batch of spot putty. I recommend the best you can buy as it sands better than the cheap stuff, doesn't clog the paper and finishes out better. This will only take one coat to do the job because after all the spot putty is just high grade body filler and fills deep pits quicker than 2-3 coats of primer. You can apply the putty with a spreader or your finger. Shallow pits seem to fill better with a finger rather than a spreader as your finger will push the putty deeper to the pit and a spreader can merely drag a thin layer over the top of the pit. On very small areas I have used a razor blade to smooth the filler after appying with my finger.

Do not use laquer based primer for this operation as you will have to let the primer dry and each coat will take twice as long to dry as the previous coat. This will take days to complete the depitting rather than just a few hours.

A tip about epoxy primers. They are expensive and you do not need to waste any more than absolutely necassary. If you have a large are to prime out and work on you can mix up what you think will be enough to do the entire area. If you know it will take more than 2 coats then you can safely mix up a large enough primer to do all you need to do ahead of time. If left in the cup and at room (shop) temperature, the primer will dry and set up in about an hour. If however, you keep the cup in the refrigerator you can keep the primer from "kicking over" (starting to harden) for about 2-3 hours. Just take the gun out long enough to shoot the required primer and then back into the fridge with it. AT the first sign of thickening you can add a touch more reducer to it, finish spraying and use up the remainder. CLEAN THE GUN RIGHT NOW!!!

Good luck.

Fill and Prime is just a thick primer like any good primer.

Epoxy based (multi-stage) primers are able to be mixed in varying degrees of thickness for different applications.

If you use the primer method to fill pits and are worried about cracking due to flexing, you can use a product called "Bull Dog Adhesion Promoter" mixed into your primer. It will make the primer take a little longer to dry but it does add flexiblity to it.

Makes for tough sanding however. Ever try to sand flexible plastic?