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Bondo over epoxy primer question?

Discussion in 'The Hokey Ass Message Board' started by billsat, Mar 14, 2010.

  1. billsat
    Joined: Aug 18, 2008
    Posts: 418

    billsat
    Member

    I've sand blasted my car down to bare metal and sprayed it entirely with epoxy primer to seal it. Now that we're beginning our bondo work, I'm wondering if I need to just scuff the areas needing smoothing with 36 grit, or do I need to take them down to bare metal prior to applying the bondo?
     
  2. OldoginMd
    Joined: Dec 20, 2008
    Posts: 295

    OldoginMd
    Member

    You ask 2 questions but need to clarify one thing ..Is etching primer and epoxy primer the same thing ? I thought they were different
     
  3. Hank
    Joined: Feb 18, 2005
    Posts: 234

    Hank
    Member
    from Wisconsin

    It depends on the filler. Some bond better to primer and some to bare metal.
     
  4. Patman187
    Joined: Dec 7, 2008
    Posts: 122

    Patman187
    Member
    from Nebraska

    Just depends on what filler you are using I know that most of evercoat's products will go over epoxy with a 80 grit scratch to hold onto.

    Pat

    www.CustomRidesbuiltmine.com
     

  5. billsat
    Joined: Aug 18, 2008
    Posts: 418

    billsat
    Member

    My mistake - I caught it about the same time you did. I used epoxy primer, not etching primer. I;ve changed that wording in my title line. I'm using Evercoat Rage applied over the epoxy primer after scuffing the surface with 36 grit paper. I'm sorry to sound so stupid, but I've heard several different answers and I don't want to screw this up.
     
    Last edited: Mar 14, 2010
  6. pimpin paint
    Joined: May 31, 2005
    Posts: 4,937

    pimpin paint
    Member
    from so cal

    Hey,

    I like 50 grit production paper, prior to filler, over epoxy for more ''tooth'', but never filler over etching primer!

    Anywhere you sand through to bare metal, should be reprimed with epoxy, prior to the application of filler. I like polyster primer for a fast build over your plastic filler followed by another two coats of epoxy, then a top coat.

    '' Meanwhile, back aboard The Tainted Pork"
     
  7. 56oldsDarrin
    Joined: May 9, 2009
    Posts: 396

    56oldsDarrin
    Member

    The only problem I have had is that if you sand through the epoxy (ppg's DP series)
    the feathered edge tends to swell when more primer is applied,then it shrinks after a couple days.
    if you can feather your filler with out cutting through the primer your fine.
    but when I did it I cut through, then my body work showed (a month later)
    Maybe if you let the filler primer cure a couple days you would be fine.
    just my opinion
     
  8. OldoginMd
    Joined: Dec 20, 2008
    Posts: 295

    OldoginMd
    Member

    Scuff it and go... if you go to the bare metal ..use an etching primer. Use something better than Bondo though
     
  9. mattfink
    Joined: Jun 1, 2009
    Posts: 107

    mattfink
    Member

    Bit of 120 grit should be fine! In my opinion you should never actually sand through the epoxy.
     
  10. OldoginMd
    Joined: Dec 20, 2008
    Posts: 295

    OldoginMd
    Member

    Mfink ., never thought of that ... keep the epoxy
     
  11. LM14
    Joined: Dec 18, 2009
    Posts: 1,937

    LM14
    Member Emeritus
    from Iowa

    How about body work over etching primer? If the primer sits over the winter would it let enough of the "gasses" escape to allow body work over the primer with a scuff to the primer?

    Thanks,
    SPark
     
  12. davis574ord
    Joined: May 21, 2009
    Posts: 785

    davis574ord
    Member

    Grind the primer off with 36 grit and feather around it with a d.a. Sander with 80 grit and you will be fine you dont ever put filler over primer, sealer etc.!
     
  13. mecutem
    Joined: Oct 6, 2002
    Posts: 603

    mecutem
    Member

    Epoxy primer is a 2 part catalyzed product.......... rattle can etching primer is not. I have found filler does not adhere well to etch and acid etch type primers. I have been putting filler over DP for a long time. Way back when I did an adhesion test. I sprayed the rear edge of a door with dp and left a spot bare metal. Smoothed the filler over both areas allowing filler to roll over the door edge somewhat. I sanded most of the filler off outside of door leaving that little curl on the edge. I then broke the filler off the edge. On the bare metal spot the filler broke off clean from the door. On the DP epoxy area the filler broke leaving a small amount of filler still clinging to the primered edge.

    DP epoxy is a good choice if you need to have your parts set around a long time before being smoothed. It has worked out well for me for many years.
     
  14. metal man
    Joined: Dec 4, 2005
    Posts: 2,949

    metal man
    Member

    PPG's dp series is created to be the first thing to touch bare metal and to have filler applied over it . Many good painters have been doing it for over 20 years now and it holds up wonderfully . I have a lot of experience with it as well . Mine has been that way since 1988 . No problem .
     
  15. The37Kid
    Joined: Apr 30, 2004
    Posts: 28,179

    The37Kid
    Member

    So the general rule now is DP over freshly sandbasted metal NOT plastic on bare metal?
     
  16. kenseth17
    Joined: Aug 16, 2005
    Posts: 69

    kenseth17
    Member

    A roughing up with 80 grit (A boat builder place I worked for even went as fine as 180) should be fine for good modern fillers to stick to the epoxy. If the epoxy is still in its open window (usually 3 to 7 day time depending on brand), then you really shouldn't even have to rough it up first, but I always do just for my own piece of mind. Grinding metal with 36 and applying over bare metal as old tech. It still works and worked for years, but todays filler stick much better and don't need that course of a scratch, and I like having epoxy sealing the metal underneath bodyfiller that will suck up water like a sponge if ever given the chance, and feel its a much better way then the old way of doing things. Plus its nice like you did, to have epoxy on the baremetal right away to protect it from flash rusting.

    Etch is a different story. Most I seen recommend not applying filler over, nor over bodyfiller. The acid and the polyester don't get along well, and the etch can cause the filler to stay soft underneath and never properly cure. Now if you wait long enough that all the acid is gone, then maybe okay to apply filler over, but when do you know? Etch I feel is a waste of time and money in most cases, as can cause many compatability problems for a product that ain't all that great anyways.

    I haven't used ppg dp epoxy since it went lead free. Probably a good thing when I read problems others have with it. Lifting at featheredges, being able to be wiped off months later with thinner, ect. Think I'll keep using epoxy I have been using, that is half the price, doesn't soften with thinner or lift at featheredges, still has zinc, Drys fairly glossy so can see how bodywork is looking, and can usually even dry sand it the next day, and had the best adhesion in a redneck adhesion test comparing different epoxys-test panels shot with a 12 gauge.
     
  17. metal man
    Joined: Dec 4, 2005
    Posts: 2,949

    metal man
    Member

    That's right .
     
  18. metal man
    Joined: Dec 4, 2005
    Posts: 2,949

    metal man
    Member

    So which epoxy primer have you been using ?Half the price is interesting.
     
  19. 1964racecar
    Joined: Nov 14, 2008
    Posts: 32

    1964racecar
    Member

    All good stuff. I use the green wash primer over fresh media blasted metal till im ready. Skuff, then Dp then after your done with filler. I shoot 2 coats of dp then shoot k36. "wet on wet " as they say. let that sit for a couple day's. long board, do any little spots with putty, k36 again, wet sand and shoot color. There are all kinds of diff way's, this is quick for me and comes out great. Putting the filler in the dp envelope you don't get any movement. the k36 sands like butter dry and gets the panel flat. Just my 2 cents. Good luck. If you do it yourself it will look great.
     
  20. brucer
    Joined: Jun 5, 2008
    Posts: 332

    brucer
    Member
    from western ky

    ive seen autobody guys scuff with the rough scotch-brite pads and go with rage.. saying they want the epoxy covering the steel not the rage..
     
  21. Nicholson
    Joined: Aug 9, 2006
    Posts: 169

    Nicholson

    Never had a problem with body filler over epoxy primer..... been doing it that way for at least 16 years. I have always lightly sanded it first with at least 180 grit.
    Never ever put body filler over etch primer.
     
    Last edited: Mar 15, 2010
  22. Andy Carter over at Pangea Speed has this to say:

    "ALWAYS spray your raw metal with sealer before puting any filler down. What allot of people dont understand is that when you mix up filler it causes a chemical reaction that creats heat. Heat on metal will draw moistier out of the metal causing condensation to form between your metal and filler. Then you get rust forming under your filler. Ever wonder why those hack fill jobs always wind up with rust under the filler? Well thats why."
     
  23. 56oldsDarrin
    Joined: May 9, 2009
    Posts: 396

    56oldsDarrin
    Member

    I dont know about chemical reaction, But most fillers use talc as the filler, like talcum powder it will suck moisture out of the air.
    Any pinholes in the metal will let moisture in cause corrosion.
    Fiberglass fillers would be used here,(over welds too)
    If you mix the new DPs 2-1-1 using reducer for the last "one" they work alot like they used to, most problems came from them being applied too thick.
    But I have had very good luck with the DP clones out there, Transtar is one I can think of.
    Remember the metal MUST be warmer than 55 degrees for any chemistry to work, and Epoxy needs at LEAST 8 hours after you spray it.
    A little extra reducer (2-1-1.5) will help the primer soak into sandblasted metal and let it flash between coats (15 minutes is a bitch, when your priming a couple parts)
    It still is the best stuff for keeping parts good until your ready for them.
     
  24. 56oldsDarrin
    Joined: May 9, 2009
    Posts: 396

    56oldsDarrin
    Member

    Now, epoxy over primerfiller is another story all together (I'm opposed).
     
  25. kenseth17
    Joined: Aug 16, 2005
    Posts: 69

    kenseth17
    Member

    Southern Polyurethanes. Okay don't know if its half the price, since I haven't bought dp for ages, but wouldn't doubt it is. Mixes 1 to 1, so about 30 bucks for a qt of epoxy 30 bucks for qt of activator, 60 bucks for 2 quarts mixed.
    http://southernpolyurethanes.com/Pricing Info.htm
     
  26. metal man
    Joined: Dec 4, 2005
    Posts: 2,949

    metal man
    Member

    Wow, those are good prices . I have not bought dp for about a year ,but I know it's a lot more than $120 per gallon mixed . Thanks .
     
  27. bigguylilroof
    Joined: Jul 1, 2009
    Posts: 210

    bigguylilroof
    Member

    dude, if you epoxy, all you need to do is scuff area well with 180 and bondo over,what is the point of epoxy if your going to turn around and 36g the area? put it like this....epoxy sticks better to bare metal and polyesters stick better to epoxy than bare metal.
     
  28. Steelsmith
    Joined: Feb 5, 2007
    Posts: 581

    Steelsmith
    Member

    I agree with 'Brucer' all the epoxy needs is a rough scuff with a scotch-brite to remove the 'gloss' from the DP epoxy. Rage has great adhesion qualities and is designed to go over DP and then be sealed with K36 or similar sandable primer.

    Be forwarned! If you use a hi-build primer like K36, block your work for smoothing and then intend to seal with epoxy, wait for a 'full cure' of the underlying K36 before you seal it with epoxy! This holds especially true in cooler climates where the cure is slowed down by winter temperatures, or if you are in a humid invironment.
    The K36 may need a week or more cure time before you can safely seal it with epoxy.
    If you don't wait long enough the epoxy seals in the solvents from the K36. Those solvents have no hwere to go but back into the filler! The filler then softens and is easily damaged as if there wasn't enough hardner used. This can be 'fixed' by opening the topcoat of epoxy primer to allow the K36 solvents to vent. I can't say what this does to the filler underneath as far as adhesion goes. When it happened to me, I just stripped off the filler and started over, it was a mess!

    Dan Stevens
    dba, Steelsmith
     

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