The Stovebolt Site Forums The Shop Area Paint and Body Shop quick sanding bondo

I have a cheese grater and a pretty good da sander. Will the d a do a decent job of quick sanding the initial coat of bondo? I've been watching lots of body shop videos on youtube, and most of those guys use what they call a bondo hog. Since this is probably my last project, I don't really want to sink hundreds of dollars into a sander. I'd like to use some sort of powered tool to rough cut the bondo, and then finish subsequent coats by hand. Any suggestions.

I’ve used files and horse ferrier rasps in the past. Be careful though. They cut quickly.

Yes DA with 80 grit will bring it down. Slowly but surely. There should not be that much extra bondo?

The bondo is not thick, but it is spread over a pretty large area. Plus, I'm not the best at spreading it.

A DA will cover a lot of area. Sit down if you can by raising or lowering truck. I use a DA and an old fashioned square face "orbit" sander for the major removal. I use a big fan to blow right where I'm sanding. Cools me, the sander and keeps the dust away from mask. Mask is a must.

HEAR YE, HEAR YE:
I don't know how thick or rough you have it BUT most body men would probably NOT use a DA. I do, but it is to get it to where a real body man can finish. Mostly of my work is just covering patch welds. So I don't want to encourage or discourage anyone. I can not finish a panel good enough to paint. When I think it is as smooth as glass, then paint, it looks like cellulite with pits. A DA is better suited for paint removal down to bare metal. I use it for that mostly, as well as a wire wheel.

The proper method for filler is block sanding. I realize you know that and are asking about "rough cut". Pro's will rough cut with graters and block sanding with 80 grit. I would not sand a whole panel or a whole truck if you paid me. It takes FOREVER!!!! and you will never get it smooth and "straight" for primer/paint.
Anyway that's what I think.

A Stanley Surform file or plane would do the job. They'renormally used for woodworking, but would do fine on bondo. They're relatively cheap, and won't break the bank. Get the longest one you can find to use for roughing out bondo.

Way back when I was 16, I made a trade with a local bodyshop (it was a one man shop) to help bondo and sand a few cars in exchange for him painting my '68 F250.

He was very clear, over and over and over, how much he HATED to sand, so he stressed how important it was to learn how to apply and form the bondo for the least amount of sanding necessary.

His advice was something this...

Plan your body fill before you start, have a plan.
Get the right tools to smooth and contour
Apply with a wide knife, knock down and smooth with a wider knife
Under filling the first pass is ok, over filling is not ok
Know when to stop working it and let it set up
If you get frustrated with how a spot is working out, go drink a Dr Pepper and then move on to another spot.

Good advice, and I'm following it. Maybe I should have explained what I'm trying to do. My doors were very badly rusted. So I cleaned them up and welded in new inner and outer bottom skins. The inners worked out fine. The outers puckered up at the weld, all of the way from one side to the other. I knew to make sure to had a proper welding gap, and I did. I also went slowly, and constantly moved around to the coolest areas of the door while welding. I took lots of breaks, in order to not overheat things. But, I still ended up with a outward pucker at the seam. I'm going to guess that it's approx. 1/8 inch tall. I guessed that I could build up on both sides of the weld and smooth it into the contour of the door, mostly because I don't know what else to do. This has turned out to be more difficult to figure out than I thought. I just bought a 24 inch sanding block, which I think will help. I also found out that buying fresh filler helps a lot. I have thought and thought about this, and finally think that I have a plan. It's gonna be lots of work, no matter what. Maybe my whole approach is wrong, I don't know. I have a lot of experience in many aspects of repair / restoration, but very little experience with sheet metal welding, and body filler. Need body work for dummies. I think that Ive watched every video on youtube on the subject, and read a thousand posts in it here.

I suggest you planish the welds to flatten them.

I must admit that I don't really understand planishing, or what it does. I did see in the videos, using a hammer and dolly to flatten the welds. I assume that this is planishing. I did try this while doing the welding, although I didn't really know what I was doing. I gave it up because there was no way to get to the backside of the welds with a dolly, or anything else, so the steel just sprang when I tapped it. There's nothing on the backside of the metal in that area to support it, so it's pretty springy. I did grind down the welds, and while it did make it look pretty nice, the ridge or pucker at the seam was still there.