I have some areas with a layer of bondo that are pretty long. How do I get them flat? Just keep sanding on them with a long board and 150 grit till they even out or I hit metal? I've smoothed them with DAs but those have to be too small to get a quarter panel or hood really straight. Also my sail panels(I think that's the name-between the rear window and c pillar) are wavy....same deal, 150 grit on the longest block I can fit? maybe 80 grit? I've gone this far, id hate to keep it all wavy. Maybe I should worry about the waves when I get it shot with high build primer? I was thinking I should have it straighter than it is now before priming, but I dunno what the heck I'm doing. Thank you fellas!
I assume this is old bondo, regardless... Ideally you want to remove the bondo and rework the metal till it is straight. Now bare in mind my knowledge is better then my technique. You don't want bondo any thicker then an 1/8 inch. So I have read. I have been trying to make sure it is no thicker than 1/16
You're right of course, that would be ideal. Unfortunately I'm losingmy workshop and don't have time to do that. Some is old bondo, some is new. Id love to strip it to bare metal but its just not in the cards this time around.
The best way to get large areas straight is skim coat the entire panel, then block it with 80 grit with the biggest block you can fit in the area and still be able to work the block. 150 grit is too fine and will polish your ripples instead of remove them. Block the area left/right, up/down and both diagnals useing some sort of guide coat. I like Duplicolor red/brown primer with the fan spray tip, it does not clog the paper at all. Once your panel is straight, guide coat and block with 180 or 220 grit and you are ready for filler primer. Yes, sanding Bondo sucks. -Abone.
Thanks, Abone, I kinda thought I was pissing up a rope with that 150 grit. I'm gonna hit it right now!
long block with 80 grit and guide coat, nothing gets "straight" in 150-180 grit.once straight you can drop down to 180 before primer. just remember it takes time + experience to do it quickly and correctly so just concentrate on one or the other. 20+ year bodyman.
A guy who made precision optics explained this to me one time years ago: FIGURE, then FINISH. You need to establish the "figure" or total shape of the panel, then you "finish" the panel with finer grit to get the smooth surface you need for top coating. All the advice above is correct, use a coarser grit and the longest board you can get on that panel. Once you see steel, STOP. The bondo will "go away" faster than the steel if you keep sanding and your waves will get worse. Everyone has slightly different methods in finishing panels but remember that high build primers typically sand easier than regular filler because they have a lot of talc in them and they will cut like mad with 180 or 220. I have been using a polyester high build lately but you need a 2.2 tip in your gun as you're basically working with sprayable bondo. I have had the most success shaping the panel with 80 grit, spraying a couple coats of polyester primer, blocking that with 220, then another coat of poly, sanding that with 320 and then killing the sand scratches with 400. If you're going to use a BC/CC topcoat system, finish the panel with 600 after the 400. Funny you should ask this question today, I'm at my garage computer taking a break from block sanding my 40 Ford!
You can make a long board sanding block using plexiglass. Get it 1/4 thick, cut it in length to handle two to three longboard sticky sand paper. Get two strips cut the same length, and glue it in shape of a T. It's light weight and very flat. Block sand away in large X pattern moving across the panel, never stay in the same spot. When metal starts to show, skim coat it again, guide coat it, then do it again. Make sure the metal that shows thru is not just high. Once you get it as even as possible. High fill prime it. Start sanding process again with higher grit paper. Remember to move across the panel. I made a 4 foot block before and used them on old VW buses. A friend of mine had a 6 foot one, it was a two man job, but the results looked better then a mirror.
Thank you for your advice, gentlemen! I'm dripping sweat but ill be damned if that sail panel doesn't look smoother! I have to run my hand over the opposite one to remind myself how bad it was. I blocked the body in 150 and was going to go 220 before hi fill primer FWIW. hopefully that's somewhere near correct. I had some of that guidecoat powder, amazing stuff, now I can't find where I put it for safekeeping! I can see a primer run in my future.
Use a X pattern when you are block sanding. Use 80 grit paper on a long block. Also you have to know when to quit sanding, might take more skim coats of filler.
ok I dropped to 36 grit to shape the bondo, then 60 and 80 with guide coats. I'm sure it ain't perfect, but I know its a helluva lot better than it was. To be honest, I'm kinda amazed. I never thought id get those smooth. Ive done funner things but it really ain't bad.
i may be old and crusty and dont know which panels but i use 36 on a Atcoa Viking air file and use a straight edge to rough it out and mark with pencil the low spots then move up to 40 then 80 or therabouts then start with the mixable spot putty and finish by hand with a long block I also use a weak Chaicago Peumatic one with 80 to 100 grit air file on the spot putty after sanding 5 imes it gets pretty good, used to do trucks and got them done a lot faster but gotta have show car quality nowdays caution air files may make hands numb and tear out your shouder joint if it has defects, ask me how i spent the last 2 years getting pain free
Thanks Eugene Vic! I have a harbor freight line sander I was about to toss since it was so weak. I just figured my compressor was too small! I'm glad I kept it, as some air powered help would be a welcome relief from this long board! I got those problem areas in some kind of shape, making other problem areas stand out all the more.
Johnny1290, How's the bodywork on your 51' coming along? Having recently finished my 50 club coupe I know what a pita they can be, not a flat panel on the whole car. I had a huge assortment of sanding blocks but what worked the best for me was a piece of 1 1/4" pvc pipe about 24" long and alot of stick on sand paper. It bent enough to conform to the shape of the panel and was stiff enough to take out the waves. Good luck
Has anybody got any suggestions for fixing waves after topcoat? After laying down some single stage it has really shown up my sub par body work and the panel is waving at me quite a bit and not sure the best way to go about fixing it. Any suggestions or has the horse bolted and I am faced with a sand back and start again?
very minor stuff you may improve by a carefull 800/1000 and re clear , but it would only get real minor stuff not big ripples
I also use 36 grit for filler for the main shape then lighter grades after that I also put a steal ruler and bend it over on an angle and check for light for highs and lows and close your eyes and feel if you can't see your mind won't play tricks on you from seeing bare metal and filler then always guide coat good luck
After doing some reading I am going to try and really pinpoint my problem areas and hopefully smooth out with the paint stirrer and paper trick and go from there. I had done the steal ruler bit but I also can say I rushed a few steps and now am paying for it! Thanks for the replies.
like i told people doing this long ago, there is just no shortcuts you have to do the work then ater they mess it up and have to do it over then they come and say you were right i did bodywork for 20 yeRS AND NOW I HAVE TO REDO IT 5 TIMES TO GET ANYWHERE RIGHT ops but emphasis in right place
The Jalopy Journal
