As usual, Eric and I are on the same page.
Must be the "Midwestern" thing. Or we have too much time on our hands.
I avoid both 36 and 40 grit.
Stick with 80, finish with 150.
My preference, is to have the panel straight enough that you can use ONE (1) coat of chemical filler, cut with 80 grit.
Next application is ONE (1) coat of polyester glaze, finish with 150.
Apply Two coats of catalyzed primer surfacer, block with 240 grit. Dust a guide coat over the primer surfacer before blocking.
If you like, apply one more coat of primer surfacer, guide coat, reblock. Can use 240 or 320, depending on Paint Manufacturer's recomendation.
This system will produce a straight panel, minimum film build, no pin holes missed, no sand scratch swelling.
On restoration repairs, I strip all original finish, so all products are compatible. No feather edging into old finish is required.
On welded joints or areas where a deeper fill may be required, I will use a product like Metal to Metal or Aluma-lead for first fill. Cut with 80 grit.
The only time I will use the coarser grit (36-40) is to knock off the very top of filler surface, cut through the oily glaze. Then use 80 grit for the real work. The idea is that there should no 36 or 40 scratches in the filler remaining, after 80 grit use, prior to prime.
This is not the fastest way, however it will consistantly produce superior results.
Karl
