Etching primer is to be used first. So, does that mean use bondo over it?? or do the metal and bodywork first then use the etching primer, then the primer sealer?? Thanks.

i use etching primer first then body then high build. the etching primer is their for corrosion pervention and not alot of people know that bondo actually gets hot when it is curing. well hot bondo on a cooler body panel and what do you get between the two.....condensation aka water which inturn causes rust. not saying some people dont do it the other way its just the way i was taught and its they way i do it.

How would water get between the bondo and the metal, unless there's water in the bondo?

I have allways seen it used over bondo. I have many friend in the body shops. Like bmw,ferrei,lambo, ect.. And allways the same.

So say you prime then bondo then sand alot of the primer off so then what reprimer? before finish layer?

the water in the air. like on the outside of a cold glass of water on a hot day. they water isnt seeping through the glass. its from the surrounding air.

Warm bondo can't cause condensation to form on the panel. If anything it would warm the panel up to make condensation less likely.

i have many friends the the autobody industry too, the people i work with. thats what i do and thats what the guys i work with do. im just telling what i was taught and what other people have told me. and yea after your body work is done then use high build primer. its thicker than etching and is used to fill in light sand scratches and help the paint bond. Then sand that down smooth with a finer grit paper like 220 then 320 then wet sand with like 600. of course its always nice to use guide coat before you sand with 220 and 320 to make sure you have all the small stuff out.
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im not as smart as i may think but i pretty sure the bondo and metal wouldnt heat like they where all one object. espicially since its the bondo conducting the heat not the metal. are you in the autobody industry too apeiron.

I grind the paint down to metal and then put a light coat of etch primer from a rattle can on

then I take some 80 grit and scuff before bondo

after sanding I take the rattle can of etch and hit all the exposed metal

body fillers are designed to bond to bare metal. always do your body work first then do your paint work.

OK, lets say you have pitted metal. You can't grind all the metal off or
it will get to thin.

1.If you bondo over rust, it will keep growing because bondo is porus right?

2. you etch the metal so the rust does not progress right??

The paint store says you cannot use it over bondo (etching primer)

I was thinking etching the metal, then priming, then some light bondo work.
Does that sound about right??

most, and i say most because i only no for sure of the kinds of bondo we use , new body fillers are designed to use on scuffed, painted areas. and if the paint store said not to use it over bondo then i probably wouldnt use it over bondo. and your plan of attack sounds good snowflake. as you see most ppl agree to use the etching primer first. may not be for the reason i was told but it is still the way everyone else is telling you to do it too.

COOL

you never cover up rust. any pits you cant remove you need to blast out. if your worried about effecting the filler then just use epoxy primer. im not so sure i would trust the etching primer to rid you of all the rust. good luck

you cannot just put any primer on rust and expect it to stop rust. etch primer usually doesn't prevent rust anyways, it is there usually only for adhesion. a good epoxy primer is the best for preventing rust, but even then it wont prevent rust that is already there from growing.

you must first remove rust, then worry about primers.