Why is 'bondo' used on flat panels before primer/top coats?

[MikeyT]

Why is it on shows such as Overhaulin' and American Hot Rod, that even after getting cars blasted and discovering the panels in good shape, they always seem to then cover most of this good metal in 'bondo' as they cal it - filler round these parts? Is it because the metal, while 'flat' may have a slight unflat surface after years and years? Or be slightly wavy? I guess they are dealing with these resprays day in and day out so know what works best - just seems a bit strange to do this as I don't think it's the norm over here is it?

?? Just curious!

[anonymous-user]

I think over here for a show finish the paint shop would use a spray on high build primer, then flat it back with the help of a guide coat to remove any high or low spots. Not sure why they put filler on by hand.

[ELAN+2]

Even flat panels have slight imperfections and ripples, I've watched a "skilled" guy apply filler by hand that looks smooth before he started sanding, after sanding with a long blockbare metal is exposed in patches, showing the high points. he applied hi build after this .

[MikeyT]

[quote=ELAN+2]Even flat panels have slight imperfections and ripples, I've watched a "skilled" guy apply filler by hand that looks smooth before he started sanding, after sanding with a long blockbare metal is exposed in patches, showing the high points. he applied hi build after this .[/quote]

Thanks for he replies, obviously this first skim filler coat is *very* thin ... maybe a mm or less? I supoose once it's on there, even if you end up with a 1mm covering, it's not going to be noticeable and it will be flat ...

If you spray a black guide coat, I presume this goes on before the high build primer? Or after, to pick out any really small imperfections?

[ELAN+2]

guide coat is usually used on top of the primer, to highlight small imperfections, like scratches, I believe

Mark

[Davi]

MikeyT said:

If you spray a black guide coat, I presume this goes on before the high build primer? Or after, to pick out any really small imperfections?

The black paint you see put on, on some of the shows is an epoxy paint to aid the adhesion of the filler - body filler doesn't stick very well to metal, the epoxy does, the filler sticks excellently to the epoxy, so you prime in epoxy, filler on, sand all back. Stops (or limits) break out of the filler.