Paint over Bondo

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Tim McIntyre

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So I've restarted the restoration of my 70 Dart Swinger. I had a door to replace the one on the car and started to sand it. I noticed some paint that was cracked. After sanding done I realized the paint cracked over some Bondo work. My question is was that a result of poor Bondo work or improper prep for paint? I want to be sure if I prep and paint over this Bondo, I won't have the same problem. Thank you.

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Dont gamble. Sand or grind it all out and redo it yourself. This way there are no doubts
 
Where there is body filler, there is normally some putty also, filling fine scratches and pits or pin holes (like spackling on drywall). Those products have chemicals in them that paint can react to. I thinking there wasn't a good primer sealer applied over the bodywork.
 
I agree. I apply my filler to bare metal and once I’ve blocked it all out I spray 2K epoxy over my body work. With the 72 hour window I then spray my high build primer to cover any scratches or pin holes to avoid using glazing putty at all. I block the entire panel after it is buried in high build then seal that just prior to paint. It is a lot of steps but I’ve had great results.

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You never know how deep it is, unless you remove it. Someone may have skimped on labor getting all of the dent out. I would get all the filler out, inspect the metal under it and work it out if it needs it. All you want with any type filler is the lightest possible skim coat you can get by with. It's not made for rebuilding body parts, just for filling in small imperfections. A lot of people get carried away.
 
I agree. I apply my filler to bare metal and once I’ve blocked it all out I spray 2K epoxy over my body work. With the 72 hour window I then spray my high build primer to cover any scratches or pin holes to avoid using glazing putty at all. I block the entire panel after it is buried in high build then seal that just prior to paint. It is a lot of steps but I’ve had great results.

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Jim that looks fantastic! Looks like your passenger agrees!

I agree about no glazing putty. I don't like it, either. It's more fine than regular body filler and tends to flake off more.
 
Ya never know
I saw a guy once doing body work on a large hole in the quarter. He didnt remove the rust, stuffed newspaper in the hole, slapped it fuli of bondo and called it good
 
Sounds like one a seen almost 20 years ago. He built an entire driver side rocker out of paper mache then mudded over it. Needless to say i lost total respect for that guy
 
Dont gamble. Sand or grind it all out and redo it yourself. This way there are no doubts
Let me go one step[ further. This is just my humble opinion, but use a good quality filler. Bondo is OK, but it does not sand nearly as well as, for example, Evercoat Rage Gold. I always use Rage Gold, and it is much easier to use, shape and sand.
 
Ya never know
I saw a guy once doing body work on a large hole in the quarter. He didnt remove the rust, stuffed newspaper in the hole, slapped it fuli of bondo and called it good
We're discussing proper bodywork here, not janky *** shade tree crap.
 
Sounds like one a seen almost 20 years ago. He built an entire driver side rocker out of paper mache then mudded over it. Needless to say i lost total respect for that guy
I've seen stuff like that before and wondered how in the hell anyone could let something like that go......but people do it.
 
Ya never know
I saw a guy once doing body work on a large hole in the quarter. He didnt remove the rust, stuffed newspaper in the hole, slapped it fuli of bondo and called it good
That is soooo nice. I'm sure it lasted at least long enough for him to flip the car to some unsuspecting schmuck. That being said, decent patching can be done without welding. Because some people can't afford a welder, and they are on a tight budget. Get rid of all the rust and use a fiberglass reinforced filler. That stuff is incredibly hard and strong when it cures. Before the hate mail starts, I am just saying that if one does NOT have a welder, it can work. Before I started welding body work (about 20 nears ago), that is how I did it. I have had some of that work last 12-15 years. The secret is to get rid of the rust and treat the metal.
 
That is soooo nice. I'm sure it lasted at least long enough for him to flip the car to some unsuspecting schmuck. That being said, decent patching can be done without welding. Because some people can't afford a welder, and they are on a tight budget. Get rid of all the rust and use a fiberglass reinforced filler. That stuff is incredibly hard and strong when it cures. Before the hate mail starts, I am just saying that if one does NOT have a welder, it can work. Before I started welding body work (about 20 nears ago), that is how I did it. I have had some of that work last 12-15 years. The secret is to get rid of the rust and treat the metal.
We have a local car salesman in Gray that does stuff like that. He buys rubberized under coating by the case to cover stuff up. He's a real shiester.
 
so bondo, primer and then sealer... what part number sealer? Gonna start my truck body work soon and need to know. Uncharted waters for me.....sell me a straight heap that don't run....but don't sell me a runner that's all body work....
 
so bondo, primer and then sealer... what part number sealer? Gonna start my truck body work soon and need to know. Uncharted waters for me.....sell me a straight heap that don't run....but don't sell me a runner that's all body work....

Sealer is normally just reduced epoxy. Check out the tech sheet on your epoxy to see what the reduced ratio is to make it a sealer.
 
Get rid of all the rust and use a fiberglass reinforced filler. That stuff is incredibly hard and strong when it cures. Before the hate mail starts, I am just saying that if one does NOT have a welder, it can work.
Back around 1980 I had a big rust hole behind rear wheel in 1/4 panel in my Barracuda. I grinded all the rust out, put fiberglass mesh over hole, and fiberglass filler over that. Today that repair is still there no cracks, no bubbles, nothing but smooth shiny paint in that area. Like you said it works and can hold up over a long long time as well.

No a days I cut the rust out and butt weld metal in on other projects I have done the last 12 years so since I learned to weld back in 2008.
 
I have a truck hood and top off a 1989 truck my kids bought that looks like a Cheetah scratched it. A MoPar parts guy suggested I use OSPHO, after sanding just as extra rust insurance. I used epoxy primer before a bondo with aluminum. Next I used primer. I'm finished painting, but there are high and low areas from some views, that seemed to appear after I finished. It's a 20 foot paint job for sure, but I feel the body is protected. Any advice for next time?
 
I have a truck hood and top off a 1989 truck my kids bought that looks like a Cheetah scratched it. A MoPar parts guy suggested I use OSPHO, after sanding just as extra rust insurance. I used epoxy primer before a bondo with aluminum. Next I used primer. I'm finished painting, but there are high and low areas from some views, that seemed to appear after I finished. It's a 20 foot paint job for sure, but I feel the body is protected. Any advice for next time?
Be careful with OSPHO as it should always be neutralized that is wet it again let it stand awhile but while wet, rinse with water. Some epoxy primers can react to it and sometimes months later.
I use OSPHO to kill rust where I have welded, and on metal that has pitted, etc. Good stuff but be careful with reactions!
 
When you sanded did u strip it all down. Ive seen alot of guys do repair work and when they sand they use edges or the tips of their fingers and u end up w what looks like waves. Blocking everything is your best bet especially if you're a novice
 
When you sanded did u strip it all down. Ive seen alot of guys do repair work and when they sand they use edges or the tips of their fingers and u end up w what looks like waves. Blocking everything is your best bet especially if you're a novice
I began the sanding process where the paint was chipping and it didn't take much to get to the Bondo. The lower door area filler is breaking off with the initial sanding, so it looks like I'm going to redo all of it.
Thanks everyone for your input!
 
I've learned the truth of what both of you said the hard way...use blocking, and clean the OsPro with water, dry, and any wipe dust before you prime..etc..Thank you
 
I agree with all of the above response. How long ago was that work done? Looks like Lacquer, that sat outside in the sun for the last 40 yrs. Do your diligence, no free lunch here.
 
I agree with all of the above response. How long ago was that work done? Looks like Lacquer, that sat outside in the sun for the last 40 yrs. Do your diligence, no free lunch here.
I have no idea. When I bought the car the previous owner included two extra doors he stripped off another car. This could have been years ago.
 
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