which comes first body filler or primer?

MetalEd · 10-23-2009, 06:22 PM

Not much choice, had the first rain and my car has a roof the prior owner left bare metal and we had our first rain this year. I tried protecting it last year with rattle-can primer, it rusted and wore away a lot of the primer.
So now I am stripping the roof and removing the rust.. lots of rust under the primer. No dents, but a little flat areas as I remove the rust, areas that were sanded too much prior to me getting it. I picked up some extreme rage body filler and some 2-part epoxy primer. Which do I use first?
Since I am doing it in small sections (about 6 sections including the sides and front and rear window areas with the windows removed.) So it would be nice to cover it up immediately as I get the area clean. Do I start with the thin coat of filler, then epoxy primer once the entire area is stripped, prepped, filled and sanded?
I have no garage, so this is an outside job. I am hoping to beat any other rain and do a proper primer/paint job next year after welding in new floors. But I would like to not have to remove all this work when I do that.

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boogerschnot · 10-23-2009, 06:28 PM

You could do it either way. Many people do filler first. But you could strip the roof and seal the entire thing first and then go over it to do your body work. and prime on top of that too. It depends on you.

rmodel65 · 10-23-2009, 06:39 PM

personally id strip the entire roof then prime with epoxy. if you follow your tech sheets for the products your using most epoxys have a time window to wipe filler directly over them the next day with no sanding... then you wipe sand filler then re-epoxy prime then 2k sandable .......

filler absorbs water so you need to make sure its not sitting open for long and priming first helps to ward off rust int he long run

MetalEd · 10-23-2009, 06:52 PM

Quote:

Originally Posted by boogerschnot

You could do it either way. Many people do filler first. But you could strip the roof and seal the entire thing first and then go over it to do your body work. and prime on top of that too. It depends on you.

I think it would be quick and easy to put a skim coat of filler right after I have strip each section of paint/rust and prepped with phosphoric acid. Then move on to the next section and once they are all stripped and have the filller, I can sand and coat with the epoxy primer.
Another reason I am thinking of going this way, even with the car covered at night, it has a layer of water from the cool and damp nights each morning (So. Cal. inland area!). I would have to remove rust each morning until I got everything stripped and finally epoxy primered the entire area. It's going to take at least a week since I am replacing window clips, removing and prepping windshield and rear glass track rust and working on the drip rails.
I am hoping that as long as I get each area filled each night (body filler), I won't have to worry about any other rust setting in. Just feather each area into the next and final sand/clean filler before the primer. Sound good?

MetalEd · 10-23-2009, 07:00 PM

Quote:

Originally Posted by rmodel65

filler absorbs water so you need to make sure its not sitting open for long and priming first helps to ward off rust int he long run

Now I'll have to figure out something else. Maybe a penetrating/protective coat of oil, to keep it from rusting each night. Clean it up when I have everything is done and I am ready to prime?
I saw this one a while ago.. Gibbs Penetrating oil, to protect raw metal from rust, says it can be painted over, but I would personally remove it before primer/paint. Think something like it might work in this situation?
http://www.roadsters.com/gibbs/

rmodel65 · 10-23-2009, 08:12 PM

sand. prime with epoxy then do filler

epoxy is water proof......

Adrenolin · 10-23-2009, 11:40 PM

As you found out.. all 'primer' is not equal! Cheap primer, rattle can or even 2 part is mostly junk. Most can be wiped off with a rag and mineral spirits even after its dried. NOT a good thing. Epoxy Primer, as rmodel65 mentioned is the only way to go. The other product that works is POR-15.. when properly prepped. POR will dry within a few hours to over night however after 30 days its damn near impossible to scratch. We used both extensively on our 67 and if/when I do another I'd do it the same way. I left the shell outside under a tarp for 3 months (Nov, Dec & Jan) last winter with 1 good coat of Epoxy primer. This was right on the North Atlantic in Eastern Canada with lots of salt in the air, high winds, temp down to -32* and . After 3 months I returned, chopped the car out of the 8" of ice, moved it back into the garage and found no rust on the car or scratches in the epoxy.

I was shocked since bare metal up there will flash rust within minutes and pitting can set in within 2 to 3 nights.

LynnBob Mustang · 10-24-2009, 07:06 AM

How are the rattle can Epoxy primers?
Adrenolin.. How how much POR15 did you end up using total on your car? At $145 a gallon, it isn't exactly cheap.
Lynn

MetalEd · 10-24-2009, 12:31 PM

Quote:

Originally Posted by LynnBob Mustang

How how much POR15 did you end up using total on your car? At $145 a gallon, it isn't exactly cheap.

Epoxy primers start at about $100 a gallon as well and go up from there. But with Por15, it's not only the paint, you are supposed to start with their Marine Clean and the MetalReady. Both appear to be amazing products, but cost prohibitive when others comparable products can be had for a fraction of the price.
I've only seen one actual use of the Por15 Paint, The black that was used on an engine bay of a mustang. I thought it looked odd/like crap because the person had used a brush to put it on, but it was also a HIGH Gloss look and Very thick looking. Looked like a protective coat of something, that's how I knew it was Por15 before I even asked. Maybe because of the brush on application, but the gloss did not look anything like what a engine bay should to me.
For the undercarriage and underside and inside firewall/floorboard (areas not seen), I might use it for the added protection, but too glossy and thick, just didn't look right/natural. Might look different thinned and sprayed correctly.

chris66dad · 10-24-2009, 02:50 PM

2K Epoxy (2 part) and then do your filler on top of the epoxy. If you do filler over bare metal you can get water into the filler from seams, pores or holes in the metal. This will lead to rust under the filler and eventually a rust bubble and paint failure.
Epoxy will seal the metal completely. Do not use rattle can paint. Epoxy needs to have a catylist to cure the paint and make it hard.
Look into SPI primer for a high quality epoxy for a really good price. Google it for painter endorsements on lots of forums.
Good Luck and BE Safe