Best tool to sand bondo

[74BlueFish]

I just finished priming the car and have applied some Bondoglass at the roof sail area and the quarter-panels.    I have an orbital sander but afraid it wont make the panels flat where needed.     Is a long board with sandpaper glued to it ok.    Or should i buy a pneumatic flat sander.    Not sure of the name if it but they are about 2 inches wide and 18 inches long.    Or just get a large vixen file to get everything close.  That Bondoglass sure seems hard to file/sand.

After I get everything close, should I apply a skim coat of bondo to the whole car, and sand most of it all off then high build primer?
This is what I got right now.

[74BlueFish]

Hope this pic is bigger

[72cudamaan]

First off, that sail panel joint is best filled with lead. That works best to hide the seam. No, do not bondo the whole car. That
would be insane. If the bodywork is close,then you can use a high build primer, block it, prime again,block again. Repeat until
the panels are perfectly straight. Good luck.

[74BlueFish]

I filled the sail joint with a welded strip of metal, so the bondoglass is not real thick there.  Ok just the hi build primer.  I never used that before.   You figure about 3 times of primer block sand to get done?

Thanks,
Dan

[RzeroB]

Looking at your second enlarged pic I would say you probably need to Knock it down some with a DA sander. I wouldn't worry about the DA "not making it flat" - that quarter panel to roof panel joint has multiple large radius curves and isn't exactly "flat" itself. Once you get it knocked down then take the longboard sander to it. You'll need a flexible longboard sander that can bend to the radius of the curves and give you full sandpaper contact with the work. After that block sand it. I like to use the high density foam sanding blocks - they come in all sorts of sizes and shapes making it easy to find one that is right for the work. Stick-on longboard sandpaper like 3M Stikit works good with these foam blocks.

Once you got it where it looks and "feels" right (most of the time my fingers can actually tell me better than my eyes if it's "right") prime it with a high build primer. Spray on a "guide coat" of a contrasting color to the primer. A guide coat is a light "fog", "mist", or "dusting" coat of paint and can be inexpensive "rattle-can paint". Block sand the work and note what the guide coat reveals to you - it will show you the high spots (guide coat color sanded away) and the low spots (guide coat color still present). If you find some really low spots you may have to skim on some filler. If no more filler is needed, continue to prime, guide coat and block sand until the guide coat comes off evenly at which point you will have a smooth even surface with no high or low spots.

[74BlueFish]

Thanks Tom
Ok ,  I will buy some Dura block or something similar of different sizes and start there.
Dan

[FY1Cuda]

When you get close to the point of painting the car, go over the roof seam area again.  After a month or two, the bondo there will shrink and the seam will be noticeable.  Some more sanding and high build primer should take care of it then.

[Street_Challenged73]

When you get close to the point of painting the car, go over the roof seam area again.  After a month or two, the bondo there will shrink and the seam will be noticeable.  Some more sanding and high build primer should take care of it then.

Very sound advice!! I've seen a bunch of cars at shows with a noticeable crack between the roof skin & quarter.

This is normally why the factory used lead at this joint, so it probably wouldn't hurt to do the same thing if you have access to a jeweler's torch & a couple lead bars (Eastwood.com).


Sent from the garage

[74BlueFish]

Thanks for the advice.  I'm letting the car sit for a week or so and am fixing the doors and front fenders.  Then I can install them and start the sanding
Thanks all
Dan

[getslideways]

not to thread jack here, but i am gearing up to do some touchup work in the same area.  What does everyone recommend for sanding the concaved radius curve between the top of the quarter panel and the sail area.  I have seen that Dura-Block makes a round sanding block, but just curious what others have found to work best?

[72cudamaan]

not to thread jack here, but i am gearing up to do some touchup work in the same area.  What does everyone recommend for sanding the concaved radius curve between the top of the quarter panel and the sail area.  I have seen that Dura-Block makes a round sanding block, but just curious what others have found to work best?

The round dowel shaped Durablock works great in that area. Just watch out for the ends. The block is a little long and you don't want
to dig in.

[jimynick]

not to thread jack here, but i am gearing up to do some touchup work in the same area.  What does everyone recommend for sanding the concaved radius curve between the top of the quarter panel and the sail area.  I have seen that Dura-Block makes a round sanding block, but just curious what others have found to work best?

Back in the day, I used a section of a truck rad hose about 2 1/2" around and a foot long. It's both stiff and pliable enough to do the concave AND convex areas. A half full sheet of sand paper in 40 grit is what I'd use to knock down the fibreglass, because you're right, it IS tough stuff. 

[74BlueFish]

Thanks Jimy,  Great idea.

[73EStroker]

When you take a car to bare metal the first thing that should be done after sanding and welding patches is to spray on a coat of epoxy primer - yes right on first and the bondo goes on top. The metal attracts moisture and that is what makes filler bubble out believe it or not.