Fender Body Filler?

[ivaldes1]

Hi So I started stripping the paint on my rear fenders. They seem to have a skim coat of body filler all over 2-3 mm thick. I am not sure why. Suggestions on how to proceed at this point as I've not done this before? Choices include: 1) Laboriously get down to bare metal (it took awhile to do that in the picture shown) and start over. 2) Sand off the top coat (also probably not easy) or Option 3 which is...?

[ivaldes1]

The propane torch method? http://www.secondchancegarage.com/public/274.cfm

[Kevin Pharis]

The torch works good for body filler and really good for undercoating. It’s gonna stink... but the junk will peel right off with very little effort.

If you are goin to strip the entire fender, I would get one of those 3M bristle disks for your angle grinder. They cut right thru paint and filler, and will gently scuff up the base metal so it’s ready to take the new paint work

[DanTreace]

Likely the skim coat of heavy filler was used to fill deep rust pits that would show under finish coat.

If the filler is decent shape and not peeling, you could consider using just paint remover, favorite is CitriStrip, and remove the yellow, leaving most of the grey filler. A paint scraper and stripper should get the yellow off. Hint to use, apply thick coat of CitriStrip and cover the fender garbage bag, prevents the stripper from drying too fast, let it do the work for chemically peeling the yellow.

Then sand, hand or orbital power, and level out, apply compatible primer for your finish coat. Sand the primer, may need several coats, the last coats wet sand to good smooth no mark finish for the final coats of your finish paint.

Or if metal perfection is desired, sand blast to bare. Apply catalyst primer/filler. Then sand, then fill deep spots that are uncovered with body filler. Lots of prime and more sanding will be needed to fill rust pits, dents, and other defects.

[John kuehn]

Does it look like the body filler is cracking or peeling? Whoever redid the fenders used skim coats of body filler to come up with a nice smooth and level finish.
Some are OK with that as long as the filler is not too thick.
Other would take out all the filler and go down to bar metal and use a dolly and hammer to level it out. But usually there still will be some spots body filler will need to be used. That depends on how unlevel the surface is.

You could sand most or all of the yellow color off and lightly skim over the filler to keep it level and repaint as you want.
Look at the underside of the fenders and you may can tell how much of a dent or impefections were filled in to smooth and level the top.
That could be your guide on what you want to do.

[Allan]

I would caution against sandblasting panels with a flat profile like early fenders. It is very easy to heat/warp flat panels with blasting. Take your time to strip them by other more gentle means. You may find that much of the filler will need to be replaced!

Allan from down under.