Body Filler Over Epoxy Primer - To Sand Or Not To Sand

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PostPosted: Thu Sep 02, 2010 5:53 pm
I have two projects on the fly here and I put both of them into epoxy primer last night. Two of the parts that I epoxied ( a hood and a door ) will need body work - everything else can go right into high build primer. The question here is this - should I sand the epoxy primer before putting the filler on the hood and door or can I apply the filler right ontop the primer? :roll: I have been read contradiciting things - some people say that it's good to scuff the primer with 36 or 40 grit before putting the filler on - some seem to think that putting the filler right onto the primer without doing anything is the way to go. It seems that everyone has their opwn way of doing this - what do you guys say? :?: :?: :? :? :D
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PostPosted: Thu Sep 02, 2010 5:59 pm
Hi. It depends on the area that needs repair. Pictures would be good or what kind of damage is it? Example something that needs to be pulled out and plastic filled or minor use of plastic filler?



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PostPosted: Thu Sep 02, 2010 6:24 pm
OK.. Here's a couple of shots of the hood and one of the door. The hood looks a lot better than it really is but it was full of big dents - probably from people sitting on or standing on the hood. Given the fact that those little English cars are made out of soup tins, it did not stand up too well. We got probably 90% of the damage worked out ( hammer and dolly ) where as the last guy who painted the car just filled them. Seriously - there were dents that were 3/4" deep and just full of filler. What is left now is minor stuff for the most part.
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The door has had a fulll ength patch glued and screwed on it to cover som3e serious rust issues caused from the inner beam that ran the length of the door. I want to just finish it off with some filler to hide the patch. It isn't as bad as it looks - believe me.

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PostPosted: Thu Sep 02, 2010 7:46 pm
OK. the minor spots you can scuff up and fill. The visible dents that bow in grind to bare metal pull out and fill. The hood looks like some can be still pulled out with a stinger to minimize the filler useage. Now for the door with rust patch? My question to you is was any body filler used to fill in between the patch and door after you glued it in?



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PostPosted: Thu Sep 02, 2010 8:47 pm
No filler has been used on the door yet. I ground it down to bare metal - did the same with the patch and then drilled small holes for little metal screws - then glued the patch onto the door using panel adhesive and then put the screws in to pull the patch tight against the door skin. I then applied epoxy primer over the patch and door skin once the glue had set for several days. I am not ready to feather out the edges of the patch with filler. As for the hood, I can't get it a whole lot better than it is. I am going to have to use a light skim coat of filler on it and then high build primer over top of that. Or do you think that the coatings and paint will fail and delaminate because of the heat from the engine? Probably sounds like a dumb question.. but I had to ask. I have never used epoxy primer before although I have painted vehicles - this is all pretty much new to me as I have been out of it for a few years and when I did do something, I did it old school. :D
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PostPosted: Fri Sep 03, 2010 3:26 pm
impcon wrote:No filler has been used on the door yet. I ground it down to bare metal - did the same with the patch and then drilled small holes for little metal screws - then glued the patch onto the door using panel adhesive and then put the screws in to pull the patch tight against the door skin. I then applied epoxy primer over the patch and door skin once the glue had set for several days. I am not ready to feather out the edges of the patch with filler. As for the hood, I can't get it a whole lot better than it is. I am going to have to use a light skim coat of filler on it and then high build primer over top of that. Or do you think that the coatings and paint will fail and delaminate because of the heat from the engine? Probably sounds like a dumb question.. but I had to ask. I have never used epoxy primer before although I have painted vehicles - this is all pretty much new to me as I have been out of it for a few years and when I did do something, I did it old school. :D



I put the filler on the door this morning - the primer seems dry - but when I sand the filler with 80 grit on my DA, it chips away from the epxy prinmer on the edges and where the filler is shallow, I am getting what appear to be air pockets half the size of a dime appearing. The filler is not bonding to the primer - as you see in the picture below - I can peel it off of the primer with a knife and there is no apparent bonding of filler to primer to any degree. I can not send the door out this way knowing what I know now - I have to take the entire door back to bare metal. Does anyone have any idea why this is happening? There is nothing wrong with the filler - it was allowed to set up properly and it sands nicely and it is from a can that I have been using with no previous problems - so I am thinking that it is not the filler. I am convinced of that. It is mixed properly and I have done nothing different with it than I have ever done over all of my painting experience.

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PostPosted: Fri Sep 03, 2010 7:08 pm
Epoxy primer has a window of time that you must work within when top coating. It looks to me like you went beyond your window and the result is no bonding to the epoxy.
I use filler over epoxy all the time and it never separates like that, in fact, you would be hard pressed to get them apart if you tried.
Did you sand the epoxy? If so what grit did you use? If not how long did you wait before applying filler?
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PostPosted: Fri Sep 03, 2010 7:28 pm
If your getting close to the window you need to sand.40 grit is a bit extreme.80 to 150 is adequate.



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PostPosted: Fri Sep 03, 2010 7:35 pm
'68 Coronet R/T wrote:Epoxy primer has a window of time that you must work within when top coating. It looks to me like you went beyond your window and the result is no bonding to the epoxy.
I use filler over epoxy all the time and it never separates like that, in fact, you would be hard pressed to get them apart if you tried.
Did you sand the epoxy? If so what grit did you use? If not how long did you wait before applying filler?



The primer had been on the door for leass than 36 hours. I didn't sand the primer - I was under the impression that as long as the filler or top copat is applied within 7 days, then no sanding was needed. I guess i was wrong. The door has been stripped as of right now and I am putting the filler over bare metal.
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PostPosted: Fri Sep 03, 2010 7:38 pm
jim c wrote:If your getting close to the window you need to sand.40 grit is a bit extreme.80 to 150 is adequate.


In the future, if I am using epoxy primer again, I'll just sand it to be sure. I really do prefer the old school method - body work over bare metal then prime. This entire week has been a write off with one bad experience after another. I don;t figure on doing any more body work once these projects are done for awhile until I get over this experience. :? :( :(
It's the little things that really make a difference in work and in life.
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