This article was on another paint forum:
Using body filler, by Reed Overson Last updated on September 28, 2013
Reed Overson lives in Bismarck, North Dakota, and has been a bodyman, painter, sales rep, and technical rep for thirty years.
Reed used to work as a technical sales rep for the company that makes Rage filler, and knows the chemists that developed the resin for it.
The following article contains some of Reed's thoughts on using body filler.
The resin used in Rage and other body fillers is fiberglass (polyester) resin. Today's resin technology makes the adhesion of these new resins as good as or better than most epoxy adhesives. They are designed to really stick. Also, they are somewhat flexible when used properly.
Most, or probably all, filler manufacturers design and recommend them to be used over clean and prepped (sanded with coarse 36-grit), rust-free (sandblasted), dry (free from moisture), bare metal. They will stick to epoxy primers with mechanical adhesion. Body fillers do not chemically bond with epoxies. If you put filler over epoxy primer, it has to be fully cured, with no solvents such as thinner or reducer left in the primer, and still should be sanded with a coarse grit and cleaned. In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on.
- - - Updated - - -
This article was on another paint forum:
Using body filler, by Reed Overson Last updated on September 28, 2013
Reed Overson lives in Bismarck, North Dakota, and has been a bodyman, painter, sales rep, and technical rep for thirty years.
Reed used to work as a technical sales rep for the company that makes Rage filler, and knows the chemists that developed the resin for it.
The following article contains some of Reed's thoughts on using body filler.
The resin used in Rage and other body fillers is fiberglass (polyester) resin. Today's resin technology makes the adhesion of these new resins as good as or better than most epoxy adhesives. They are designed to really stick. Also, they are somewhat flexible when used properly.
Most, or probably all, filler manufacturers design and recommend them to be used over clean and prepped (sanded with coarse 36-grit), rust-free (sandblasted), dry (free from moisture), bare metal. They will stick to epoxy primers with mechanical adhesion. Body fillers do not chemically bond with epoxies. If you put filler over epoxy primer, it has to be fully cured, with no solvents such as thinner or reducer left in the primer, and still should be sanded with a coarse grit and cleaned. In other words, using epoxy primer under filler is a wasted step that may or may not cause adhesion problems later on.