Quote:
Originally Posted by Gippetto
"Epoxy goes on bare steel to prevent corrosion.
Filler goes on bare steel too so spray the entire panel, then sand it off just before applying filler.
This is the proper process"
Question to Footstomper: When you say sand it off do you mean break the surface to give it some tooth for subsequent coatings, either paint or fillers? If you sand the epoxy off you destroy the moisture protection provided by the sealer. Filler absorbs moisture.
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The best place to answer your question is the technical data sheets on the products you are using. They are readily available on the web.
However, to give a generic answer, you should remove the epoxy where filler is going, You're going to remove some anyway when sanding the filler. The filler will absorb moisture if submerged or left outside in the rain, but because you're not going to do that and are going to high build prime and paint, the filler is encapsulated and no moisture will get to it to cause rust. This is why it's so very important to never fill holes with body filler as the moisture will cause a failure.
At the end of the day, putting filler on top of epoxy is not a bad thing that will fail, but filler likes a heavier tooth than a simple scuff, so why not give it.