Filler over epoxy/bare metal dilemma

Discussion in 'Body Restoration' started by TX79Z28, Jul 2, 2013.

  1. TX79Z28

    TX79Z28 Veteran Member Lifetime Gold Member

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    As many of us have experienced, I just had a "detour" in my project. Just a brief background: When I started the tear down almost 5 years ago....yes I know....a LONG TIME, I had NO clue as to what process or products to use for all the body work. A local jobber was great help in getting me started; however, I think I got some "dated" advice from him. I started off by stripping the car to bare metal and was going to shoot etch primer over the filler work...per his advice. Somewhere along the line, I found out about epoxy primer, but not about SPI. The jobber sold me a "sort of" epoxy, which was "Corlar mastic" by Dupont. As I found out later, this is actually an industrial coating used on OIL RIGS! I sprayed this stuff OVER the filler work, and although it was a PIA to spray, it covered fairly well.

    Well fast forward, and I found SPI and have been VERY happy with their products and customer service. After much soul searching, I decided to strip the Dupont stuff, and re-shoot SPI epoxy. With the exception of the BC, all the products on my car will be SPI, and I wanted to keep it consistent.

    As I was stripping the old epoxy, I realized I had done filler work on the bare metal. I know this is a time-proven way, and many folks still do it that way. However, for me (and per SPI) doing the filler work over two coats of epoxy makes more sense. As I was sanding, I could swear I saw what appeared to be rust under some of the filler that I hit with the DA by mistake. By the time I could look, the DA had hit what might have been slight rust, so I am not 100% sure. This brought a nagging thought into my mind, and I kept second-guessing myself as to what quality of work I did with the filler back then. Don't get me wrong, I don't know squat now (just enough to be dangerous) but a WHOLE LOT more than back then. I hate the thought of stripping all the filler work that I did back then, but this brings me to my question.....which if I am asking....I think I already know the answer.

    Since I am down to stripping to bare metal anyway, should I just remove all the filler? Shoot 2 coats of epoxy and re-do all the filler work on top of that? Oh, BTW, there is some more filler on both lower quarters still covered by the old epoxy.


    Any thoughts/advice/insight would be REALLY appreciated!



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  2. spicewood1

    spicewood1 BANNED

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    I have had the same sort of experience where I learned so much along the way that I knew the beginning of the job was done wrong. First your metal looks a bit too shiny - you should be using 60 grit fresh paper on bare metal. SPI requires 60 grit scratches on bare metal. Use a good air DA and get it all down to metal no traces of any old paint or filler. I love the SPI epoxy. You dont have to use $50 Rage gold filler but I like it.should not take but a couple days to redo your filler work and you can sleep at night...No offense but whatever tool you have laying on top of the car has no use in body/paint work.
     
    Last edited: Jul 2, 2013
  3. Z28zz383

    Z28zz383 Veteran Member

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    Strip to bare metal, corrosion barrier of good epoxy primer,(SPI,etc) then a bondo coat over the whole car to sand on with out breaking thru the epoxy primer. Then spray at least 3 coats of a good hi build sanding primer, followed by 3 more coats of surfacing primer.(correct color for base color used) Sealer, base, clear. This is my procedure for doing it.
     
  4. TX79Z28

    TX79Z28 Veteran Member Lifetime Gold Member

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    I was using 80 on a DA since SPI calls for 80 grit for epoxy, but I am sure it would fill 60 just fine. Since I'm still in the learning stage, I have a question about DA sanders. The way I understand it, when you lock the plate on the sander, it's basically a "straight" sander, not orbital, and when you unlock it, it allows it to "orbit", is that correct?

    I am stripping with the plate locked because it's much more aggressive and faster. I noticed that when the metal is bare, if I go at it with the plate unlocked in the "orbital" setting, it leaves nice scratches as opposed to the smooth finish of the more aggressive setting. So, after I strip all of it, I was going to go back and do it again to "rough it up"

    BTW, the sander you see was being used for something else...not the body
     
  5. Z28zz383

    Z28zz383 Veteran Member

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    Heat build up is the problem. Hi speed grinders, and d-a's in the grinder mode, will heat up and slightly warp the metal if not kept moving to prevent excessive heat from occurring. 60 or 80 grit orbital scratches are excellent for the epoxy to grip onto.
     
  6. spicewood1

    spicewood1 BANNED

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    I have never once used my da in the locked up posituon. Spins too fast and burns the metal. Sometimes threw sparks. Use the orbit setting and fresh paper. Keep in mind once you hit metal the paper dulls out much faster so you have to change paper every few minutes. Get the more expensive rolls too - the cheap paper is done in less than a minute!
     
  7. TX79Z28

    TX79Z28 Veteran Member Lifetime Gold Member

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    I had the Norton Gold 6" PSA roll (100 count) in 80, so I am using them and hate them! Like you said, seems like I have to change them out every few minutes. I guess I was using it locked to get this done, because unlocked it seems to take forever. I know I could get the primer off in no time with 60gr flap discs, but I am sure they are too aggressive even on the Makita adjustable speed buffer. I seem to remember that when I initially stripped the original paint, I was using (I believe) the 3M discs that peel and stick and come in a pack of I think 10. Those discs seemed to last longer and actually had a "bite" to them.
     
  8. spicewood1

    spicewood1 BANNED

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    I would guess under normal circumstances it should take an hour and maybe 8 sandpaper discs per major panel. I like to put on a fresh one at the end to go over the whole panel.
     
  9. jimbaughan

    jimbaughan Veteran Member

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    I always strip with an 8 inch foam pad with 40 grit. It covers a large surface and doesn't build up as much heat.
     
  10. ponchonutty

    ponchonutty New Member

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    Ditto on this. I like to use the K2000 primers after a zinc etch. It seems to give a great adhesion and the primer is so thick it's like you are spraying bondo. It will block out minor door dings if you spray it right.
     

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