“Cheese grater”–style body...
“Cheese grater”–style body files are great for rough shaping filler, especially while it’s in a semi-hardened state. While they’re available from tool supply houses, this is actually one of my dad’s old woodworking tools, and must be almost 50 years old!
The captions show how to mix the filler, but when applying it, try to keep it smooth with long pulls of the spreader if you are covering a large area, such as the top of a front fender with many subtle waves in the sheetmetal. You’re aiming for a thin spread of filler, so ensure any large dents are repaired beforehand. The smoother you spread it, the less work you’ll have sanding most of it off. And sand most of it off you will. I like to use 40-grit paper on a DA sander to “knock down” the filler to a level where I can take over with 80 grit on a block, and complete the job by hand. This takes practice, especially on curved panels. Longbed air sanders are available, but I’m used to using a DA. If you find you need to add filler in some areas after sanding, re-apply a spread over the whole area, not just the low section, as it’ll make it way easier to block it flat than trying to block an area of fresh filler in the middle of already sanded filler, as you’ll always end up sanding the new and the old.
Remember practice makes perfect, and this is a skill like any other, despite body filler’s reputation as a cure-all for dents and rust. Always make sure it is used over good, clean solid metal (or ’glass) and get the sheetmetal as straight as possible before applying the filler, which should never be more than 1/8-inch thick.
I deliberately mixed this...
I deliberately mixed this batch quickly to illustrate what can happen. The arrows indicate small air pockets in the filler, which will be transferred to the panel being worked on, and will come back to haunt you later. Some are unavoidable, but take your time mixing the filler to avoid this as much as possible.
Though it takes some practice,...
Though it takes some practice, I often use a DA sander with 40-grit, then 80-grit paper, to knock down the filler.
Once the filler is roughed...
Once the filler is roughed out, and especially on flat panels, it’s time to switch to a sanding block. I’ve had these for years, and love them.
OK, so it’ll take a little...
OK, so it’ll take a little practice, but applying the filler as smoothly as possible, and covering the entire area you want to fill is what you should aim for. It’ll cut down on sanding time too.
The longer two blocks each...
The longer two blocks each have three steel rods along their length. With the rods in place they’re rigid, yet pull the rods out and you can bend the blocks in half. They’re great for sanding curved panels.
Just as with the DA sander,...
Just as with the DA sander, the paper is self adhesive and simply sticks to the surface of the block. Scrape any paper remnants from the surface first though, as it doesn’t always all come away when the paper’s removed.