Two-part epoxy vs. polyester filler, polyester lost hard today

Had a 2014 F-150 rear quarter come in with about a foot of rot above the wheel well. I laid down some polyester filler to save time on the first pass, figured it would be fine for the bulk. Sanded it down after 20 minutes and it just crumbled in spots, pinholes everywhere. Switched over to two-part epoxy primer and filler blend for the second pass, took an extra hour but the surface was solid as concrete. Anyone else stopped messing with polyester for anything thicker than a skim coat?

2 comments

2 Comments

sean78222d ago

Did you rough up the metal good and use a wax and grease remover before laying that polyester down? Tbh I've had polyester do the same thing to me, but it was almost always because I got lazy with prep or tried to lay it on too thick in one shot. I still use it for the bulk of my filler work on bigger repairs, but I keep it to like a quarter inch max and let it kick off fully before I even think about sanding. Epoxy is definitely more forgiving and I get why you'd switch, but I've had polyester hold up for years on stuff when the metal underneath is actually clean. Maybe your batch was old or the hardener got mixed wrong, that stuff can be finicky that way.

carr.elliot22d ago

Prep is everything with that stuff. Clean metal or it fails, plain and simple.