Body filler question
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09-06-2008, 10:02 AM
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09-06-2008, 05:19 PM
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filler over bare metal is best. you need to scratch the metal with 80 grit paper so the filler will bond. it can go over primer as long as it's sanded also. bondo works good. it has a bad rap. i've use it up to 1/8 of an inch without failure. rage gold sands easier. lots of different products for different uses.
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09-06-2008, 06:57 PM
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Filler over bare metal is old school. You don't want the moisture in the filler reacting with the bare metal. Most restorers use a self etch epoxy primer, then you can put fillers on top of the epoxy, it has great adhesion and the application window is up to 7 days. Do some research on the epoxy primer and you'll see. JM2C
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09-07-2008, 07:29 AM
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09-07-2008, 10:35 PM
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And the debate continues, and both ways have been argued. I've done it both ways with success.
I prefer over epoxy primer. Not only does it provide the opportunity to get any bare metal covered asap, you have added protection under body filler which will soak up moisture like a sponge, and stop it from reaching metal, if the finish is ever compromised in the future, and water can reach that body filler. What about if you wetsand your primers? The only primer that is non porous and will complete seal from air and moisture is an epoxy. Back in the days whe n lacquer primer was used, A car with lacquer primer over the metal, primer that got wet or sat in a humid shop for a long enough would start having rust spots appear through the primer, a urethane primer is probably better then lacquer, but still is porous. I car and the filler manufacturers always use to recommend over bare metal. THen in the mid 90's I belive, at least icar changed there tune, and began recommending over epoxy, and also believe it was toyota that required over epoxy primer and still requires it.
The Right Primers
Around that time, it seemed half the shops stuck with applying over metal, while the other half began applying over epoxy.
Filler will stick just fine to epoxy applied in its window, or scuffed up with 180 past window and epoxy will stick well to metal and provide it good corrosion protection. Remember epoxy is slow cure, so if you want to test adhesion, allow the epoxy some decent cure time before you judge anything. Either way is fine, but I will put down epoxy first.
Also though I never really did use it, I believe if you spray etching primer, most recommend not using under or over filler areas (due to the acid in the etch and the polyester resin in the filler and affecting the fillers cure), so you would either have to remove it from the area, or use another primer over it first. Although maybe with enough time for the acid to leave maybe you would be okay. Also have to watch compatability with etch and epoxy, some might not be compatable.
When I first learned I was taught to apply filler to ground bare steel. Now fillers are improved as well and should adhere fine to 80 on bare metal and finer on epoxy out of its window (steel is harder). I car use to always recommend metal prep or etch followed by an epoxy for corrosion protection for bare steel, but I wasn't ever really a believer in using etch on metal that was clean and sanded, and just applied epoxy to the metal. I haven't kept up with i car, but believe they may have possibly changed there tune on the etch recommendation as well.
Either way again is fine. Some people are stuck in there ways, or won't try newer methods, if it seems to work for them.
Bondo will work, but there are certainatly better fillers out there. And evercoat lightweight at my body supplier is also a few pennys cheaper then bondo thats been sitting on walmart or the hardware store shelf for who knows how long, if you want to stick in the same price range. It also spreads and sands better meaning less work, and goes through less paper. Evercoat makes some good fillers, many like rage, but to me it is a bit too pricey, and don't think it is that much easier to work to justify the price difference. I did use some 3m stuff once that was on sale, and think bondo was actually easier to work then that stuff was. Bondo also has other brands that are pretty decent, marson, dynatron, and marhyde, but bondo is probably the bottom for filler.
(i just did a search, what the heck was bondo corp bought out by 3m?, must have been sleeping on that one,)
I prefer over epoxy primer. Not only does it provide the opportunity to get any bare metal covered asap, you have added protection under body filler which will soak up moisture like a sponge, and stop it from reaching metal, if the finish is ever compromised in the future, and water can reach that body filler. What about if you wetsand your primers? The only primer that is non porous and will complete seal from air and moisture is an epoxy. Back in the days whe n lacquer primer was used, A car with lacquer primer over the metal, primer that got wet or sat in a humid shop for a long enough would start having rust spots appear through the primer, a urethane primer is probably better then lacquer, but still is porous. I car and the filler manufacturers always use to recommend over bare metal. THen in the mid 90's I belive, at least icar changed there tune, and began recommending over epoxy, and also believe it was toyota that required over epoxy primer and still requires it.
The Right Primers
Around that time, it seemed half the shops stuck with applying over metal, while the other half began applying over epoxy.
Filler will stick just fine to epoxy applied in its window, or scuffed up with 180 past window and epoxy will stick well to metal and provide it good corrosion protection. Remember epoxy is slow cure, so if you want to test adhesion, allow the epoxy some decent cure time before you judge anything. Either way is fine, but I will put down epoxy first.
Also though I never really did use it, I believe if you spray etching primer, most recommend not using under or over filler areas (due to the acid in the etch and the polyester resin in the filler and affecting the fillers cure), so you would either have to remove it from the area, or use another primer over it first. Although maybe with enough time for the acid to leave maybe you would be okay. Also have to watch compatability with etch and epoxy, some might not be compatable.
When I first learned I was taught to apply filler to ground bare steel. Now fillers are improved as well and should adhere fine to 80 on bare metal and finer on epoxy out of its window (steel is harder). I car use to always recommend metal prep or etch followed by an epoxy for corrosion protection for bare steel, but I wasn't ever really a believer in using etch on metal that was clean and sanded, and just applied epoxy to the metal. I haven't kept up with i car, but believe they may have possibly changed there tune on the etch recommendation as well.
Either way again is fine. Some people are stuck in there ways, or won't try newer methods, if it seems to work for them.
Bondo will work, but there are certainatly better fillers out there. And evercoat lightweight at my body supplier is also a few pennys cheaper then bondo thats been sitting on walmart or the hardware store shelf for who knows how long, if you want to stick in the same price range. It also spreads and sands better meaning less work, and goes through less paper. Evercoat makes some good fillers, many like rage, but to me it is a bit too pricey, and don't think it is that much easier to work to justify the price difference. I did use some 3m stuff once that was on sale, and think bondo was actually easier to work then that stuff was. Bondo also has other brands that are pretty decent, marson, dynatron, and marhyde, but bondo is probably the bottom for filler.
(i just did a search, what the heck was bondo corp bought out by 3m?, must have been sleeping on that one,)
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