I've read all of the filler threads on here....I have looked at TDS from multiple manufacturers. Most have fillers that state in the TDS they can be used over factory finishes. Having said that, I have yet to find a shortstrand product that says it can be applied over primer or paint. I spoke with Evercoat (the technical department was answered by a lady with an asian accent) who did not seem that knowledgeable. She referred me to Evercoat's field rep. The field rep said to apply it over epoxy primer and not under. I have also had a couple reputable members on here say to use it over epoxy as well. I am still feeling uneasy about it when the TDS doesn't list it as a substrate. He also recommended using Finishsand 4:1 instead of epoxy. I feel like this is a no no, because it is polyester, but looking at the TDS, it says it passes 500 hour salt spray. I am using it over some welded seams, and around door jambs. Just hoping someone here has used an actual shortstrand and can speak to it.