Depending on how many pits. If you have a lot like a totally pitted frame you want smooth you could etch prime and then polyester prime it. #417 "Glaze Coat" is polyester putty. Polyester putty is a smooth "bondo".
You could sand blast the rust and then etch prime it, urethane or epoxy primer then the polyester putty also. It depends on the project.
Below is the "Basics of Basics" of "bondo" types.
"Bondo" is a brand name, it is really Plastic filler/Polyester filler. It is like how we call all tissues "Kleenex" or all adjustable wrenches "Cresents".
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"Basics of bondo types"
"Regular" polyester body filler, and polyester "putty" is basically the same thing. They are both, you guessed it "Polyester" based. Polyester is what fiberglass is made of. The fillers have talc and some other components that give it "body", that is the basic difference between fiberglass resin and polyester body fillers.
The Putties have a finer ground talc than "regular" filler. They cost MUCH more, but are well worth it for skim coats and minor repairs. Being they are polyester they use a hardener and CURE like fiberglass.
The old "spot putties" DO NOT use a hardener and are simply lacquer primer . They are JUNK and should not be used.
Some examples of these products are as follows.
"Reinforced" polyester fillers:
These can be aluminum filled body filler for metal surfaces. I is very hard to sand and not good for the finish work (needs a skim coat of a "reg" filler or polyester putty) but will fill much more per coat reg filler and has more corrosion resistance.
A Fiberglass reinforced filler is similar.
Examples are:
Evercoat's "Metal-2-Metal", "Everglass", "Kitty Hair", "Tiger Hair"
3M's 05815 Short stand filler, 05813 Long strand filler.
"Regular" polyester body fillers:
Evercoats RAGE or "Lite weight" and others.
3M's Lightweight body filler #058001
Polyester putties:
Evercoat's "Polyester glazing putty", "Easy sand" and others.
3M's "Flowable finishing putty"#05824 or "Piranha"#05821 .
"Spot putty" (junk, not recommended) Usually found in a toothpaste tube looking container.
Evercoat's "Ever-glaze" #403
3M's "Acryl-green" red or blue #05960,05964,05966
Dupont's 2286S, PPG's DFL17
I personally recommend Evercoat products.
