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Just a firefighter
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OK, I've done a really dumb thing here. I've got my '46 Chevy Panel truck and getting it ready for painting. When I got it I was the fourth owner since it was built. The last two guys did several things but stopped short of finishing it. Well the roof had the high build primer on it, so I (like a dummy) assumed it had been stripped and primed already so I was just going to sand it down and add some fresh primer over it and paint. I started to sand it down and found that the primer was over the orginal 1946 paint and alittle surface rust. Now heres my BIG problem, the rest of the truck is primed and ready for sanding and everthing I use on this paint loads up on the sand paper and even the grinding discs(and I mean really bad). With the rest of the truck done chemical stripping it out totally, won't even consider it!! Anybody know what this stuff is and how I can get it off????:pain: Help me PLEASE:pain:

Thanks
David
 

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If the primer is doing the loading, this is either under-activated urethane or Lacquer primer.
If your talking about the paint causing the load-up than it is probably Nitrocellulose Lacquer.

Two options here, take a rag and wet it up with urethane reducer
and try a one foot spot and if it come off easy than take of the majority that way than do your sanding.

However, Nitrocellulose lacquer usually comes off pretty good with a 24 grit grinder, it can load 36, 50 & 80 but 24 is really not a problem.

Nitrocellulose lacquer has really not been in normal usage since late 60's but was a favorite for restoring and was use on the Rolls until about late 70's. If thats whats on there it will be thick!
 

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3M makes a strip and clean disc that has worked really well for me on heavy layers. You can find them at some of the home building stores. They are purple in color, do not load up and come with 5/8 or 1/4 arbors. You would think that something from a home store could not work for automotive, but they work great. The finish comes out smooth enough to epoxy prime over, but I would still DA with 120 or 180 prior to priming. The DA is more to remove small nib type stuff and help uniform the finish. I think they are about $10.00 a piece. They are recommended by 3M for strippping car paint as well. 3M also has a brown scotchbrite for a 7" angle grinder that works awesome. I have only been able to get these from work so I can recommend where you can buy those. By the way, on a 46 Chev truck roof, 1 disc will do it. Maybe 2 for the length of the panel version, that is from my memory and guestimate ofcourse. Very fast by the way. If you try it, let folx here know how it worked. Try and run it with moderate pressure and about 5000 rpm. Good luck on your project.
 

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Can you give me a 3M part number for the stripping disc. I read about it on here just lately and had not heard of it before. Sounds like a good idea. I tried a regular red Scotchbrite pad on a 3000rpm sanding pad and it would not work. I'd like to find this 7" pad and try it on a grinder. Anything that would strip paint well, not generate heat, and not cause alot of unnecessary grinding disc scratches would be great. If you would supply a 3M part number, I can probably locate it.

Thanks,

Jake
 

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I don't have a part number but it is called a 3M Surface Conditioning Disk. They can be had both for a drill arbor or for a 4" grinder. You'll want the 36 grit, purple one. I buy mine at Lowes Home Center. And YES, they are about the most amazing thing I've used for removing paint and old bondo. You will want to use at least a dust mask.
If you use the grinder one, it will last best if you keep it as flat as you can. If you spend much time up on the outside edge, you'll wear it down and be left with a lot in the middle you can't really use.
 

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I do not rermember the part number either. Sorry about that. Even though it is a coarse disc number, remember it is a different type of abrasive. They are generally an impregnated nylon if memory serves me right. Anyway, very good stuff for removing old layers of paint quickly. I highly recommend a 4" grinder set up with a 5/8" arbor. If you use the full size 7" or 9" type, you will know what I mean. Heavy for that amount and kind of work. Oh, by the way, the color purple is correct. Just screw it on and have at it. Dust mask is important here. And as Julmer said, keep it flat, at about a 10 degree angle will do it. Let us know how it works for you. I would aslo do a light scuffing with a DA afterward.
 

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I bought a couple of big ones but the only source I can find for them is Eastwood and I don't like being stuck with mail order for things I tear up occasionally. They do get heavy pretty quickly, too. If you had a LOT of Bondo to remove, the big one might be worthwhile but the 4" is much easier to use. One of the big advantages of using them is that you really have to try to hurt the underlying metal. With a flap disk or a coarse grinding disk, you can burn the steel in a flash. With the 3M ones, you end up with a nicely cleaned, almost polished surface.
 
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