to epoxy primer or not, that is the question-almost!

[Carl Beck]

Hi Guys:

"Does body filler bond better to metal or an epoxy primer?" - Really isn't the question most of us should ask - is it?

It would appear that it did bond well to the epoxy... and we know that if properly applied, to a properly prepared surface - the epoxy primers bond well enough to metals.

I think the question we would want to ask is - "what is the best practice, or the best process to use if we want the results of our work (or dollars spent) to last the longest.?"

No matter what they name it (Metall etc) - nor what they call it (Metal reinforced, fiber reinforced, etc)- all modern two part body fillers are in fact man made plastic products. If they are two part compounds, one part being the resin and the other being the hardner... once you mix them together a chemical action is started and it never really stops until the plastic compounds fall apart again (granted that may be 20 or 30 years later...).

If you put any plastic filler on bare sheet metal - because the plastic compound keeps drying and drying (hardening) it will draw moisture out of the air and though the sheet-metal. Sheet metal is very porous and as rust forms on it and the oxidation process proceeds, the metal becomes even more porous.

As the body fillers draw moisture though the metal - they swell and that is why body fillers bubble up under your paint a year or three years later; especially if the opposite side of the sheet metal can not be properly sealed somehow.

All plastic body fillers should only be applied on top of something that seals the metal from the filler. Epoxy primers will do that... so a thin layer of plastic filler, applied on top of the epoxy primers is prevented from drawing moisture through the sheet metal - and if it's then sealed from the top - with a sealer, or epoxy primer, or the final coats of paint - it should be fine for many years...

The more time you can allow between applying the plastic body fillers - and performing the final sanding and paint application - the better. That gives the body filler more time to dry and shrink before it's under the final paint coats.

I believe that the bottom line is - putting plastic body fillers directly on bare metal should be avoided at all costs.

FWIW

Carl

Carl Beck

Clearwater, FL USA

http://ZHome.com