Can I use body filler over DP 90 epoxy primer or will I need to take it to bare metal where I use filler? Pops

Just scuff it with 180 and bondo right on the primer.Make sure after you scuff it you clean it good before bondo.

I would try not to go through the dp-90 if possible.when you scuff it.

I agree. Don't go through the DP 90 if at all possible.

The old school method was to apply bondo to bare metal - the thinking being that it would bond better to the scratches in the metal.

However, today it is recommended to prime first with an etching or better yet epoxy primer and then scuff the primer and apply bondo. This leaves a barrier between the metal and bondo (which is very porous) and will keep the metal from rusting from the inside out.

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I do the epoxy first then body work also. Down here with all our humidity if you are doing body work over large area and it takes you a few days the bondo acts like a sponge and and we get rust under the bondo. But as a rule of thumb I do it to seal the metal for any elements and I find the bondo has great adhesion to the epoxy also. So YES DP90 (I use the 401 activator and wait 3 days before you do any body work for good cure) then scuff( I put enough on so i don't break thru with 80 grit scuff) and do your filler. Also do the metal work before you epoxy that way you don't have any open areas from grinding,hammering etc. JMO Tim

From various sources it appears your strongest bond is epoxy on properly prepared metal. Then sand with the paper grit as found on the technical sheet for the type and brand filler you are using.

I believe most fillers tend to recommend 80 grit for metal to filler and like 180 grit for primer to filler.

SPI recommends using their epoxy and putting the filler directly to it during the re-coat window. This will cause an even stronger bond. Call the owner and ask, I did.

It is strongly NOT recommended to use an etching primer under a filler. The acid interferes with the filler's curing. Actually, it appears in most cases you are better off with epoxy than etch.

Many shop guys will tell you only filler direct to metal. They are in business and would loose money laying down epoxy first. There is nothing wrong with laying filler directly to metal. A hobbyist that is taking his time will want to seal the panel with epoxy to prevent moisture from flowing through to the metal.

Take some time to read the tech sheets for the filler you are using. Many guys are short changing the bond by using the wrong grit paper. The companies have spent a lot of money on figuring out the best grits to use for best adhesion. Adhesion comes from the scratch per inch and a certain depth of scratch. To low a grit leave too much flat space between the scratch and too high a grit is not deep enough.

Lost in NJ wrote:It is strongly NOT recommended to use an etching primer under a filler. The acid interferes with the filler's curing. Actually, it appears in most cases you are better off with epoxy than etch.



You couldn't have said it better. I forgot to bring up the acid etch primers. To put it simple bondo will not stick to it.