I guess I don't understand why other people have trouble removing old paint

[Bill Crowell]

I'm no great shakes as a body man, but it seems to me that 36 or 40 grit discs on an electric D/A takes the old paint off about as fast as I'd ever want to, plus the discs last a long time and never clog up. It also does a creditable job of removing bondo.

When I start to see primer in the scratches, I might switch to 80 grit, but maybe not. If I am going down to bare metal, I will often just stay with the 40 grit until almost all of the primer is gone and I start to scratch the metal.

I never understood why people will try to remove old paint with 80 or finer grit paper. I guess it is because they are afraid of scratching the bodywork, but I don't think that is really a problem. 80 grit will clog up almost right away.

Your opinion, please?

 

[70aarcuda]

I used 80 grit, that is what a neighbor who woulds as a body man suggested..

 

[clifftt]

The lower grits work faster, but also heat up the metal and may cause some warpage, so be careful. Also remember that there is lead, not metal, at the base of the A-pillars and somewhere in the sail panels which scratch up in an eye blink, not to mention your machine is flinging lead up in the air. WEAR A MASK!!

 

[twistedracing]

I like using both. 36-40 grit is just more dangerous if you dont keep your d/a flat as it can dig into the metal faster causing dips. I like to strip with 36-40 then go over with 80 to make scratches smaller.

 

[Alaskan_TA]

Razor blade in a window scraper will not heat up the metal. Quite fast, & very little dust too.

 

[ramenth]

A good primer surfacer will fill an 80 grit scratch in two coats. Scratch the metal with anything more and it will take more coats of some very expensive paint to fill the scratch. That being said I've never had any problems with Mirka or Norton 80 grit clogging quickly. Maybe it's the type of sandpaper being used?

Guess I've always looked at in the overall process: the smoother the sheetmetal, the smoother the undercoats, the shinier the paint will be. The paint work is only as good as the prep work. And if you miss something, like an improperly filled 36 grit scratch, in a paint job that's deep enough to read a newspaper in from 5 feet away, it'll stick out like a crater on the moon.

There's also the productivity factor to take into account at times, too. Back when Chevy was warrantying a paint job due to delamination, I could bring in a full size truck first thing in the morning, strip it of the door handles, emblems, mouldings, grille, etc. Hit it with chemical stripper to get the paint off, and then go to town on the primer with 180 grit and have it to the paint shop by noon. Nothing courser than 180 as the painters didn't want to have to block primer in before paint. They'd paint it, bake it, back to me for assembly, and it'd be out the door before quitting time. Looking better and outlasting anything the factory ever did.

 

[Bill Crowell]

I see what you are saying, ramenth. Maybe I will use a different brand of 80 grit instead, and see if it clogs up less than the paper I was using. We do want to avoid waves and gouges, don't we?

Thanks to all those responding for the good feedback.

 

[chrisf]

now that i have a soda blaster i would never take paint off any other way. this chevelle fender i blasted quickly as a experiment. (its not perfect) Doesnt leave a rough surface at all. in fact the bodyshop i do work for just cleans and shoots it afterwards. no prep work at all. (assuming it needs no work)

 

[ramenth]

now that i have a soda blaster i would never take paint off any other way. this chevelle fender i blasted quickly as a experiment. (its not perfect) Doesnt leave a rough surface at all. in fact the bodyshop i do work for just cleans and shoots it afterwards. no prep work at all. (assuming it needs no work)

Doesn't leave a rough surface at all? I've worked for a soda blaster in the past and he and I used to have fun debating this...as in what's a course enough surface for primer to stick to? Epoxy on bare metal the manufacturers like to see at no courser than 180 grit. Is the blasting process equal to that?
A good urethane or primer surfacer should be the same way, a minimum of 180 grit for metal and bone, as the surfacer needs a sand scratch to flow into and lock down on. When you say it doesn't leave a rough surface is it leaving enough surface area on the sheetmetal - that's what sanding does, increases surface area - for the primer to look on to?
Don't get me wrong, I like media blasting. Quick, easy, and in the case of soda, it's biodegradable, making clean up easy - shovel, sweep, wait for a good rain - but I've always felt the need to rough the panel up a little more afterwards with at least 180 grit. It may take a little more time, but it's a peace of mind thing, knowing that I won't have to worry about primer not wanting to adhere.
And please don't think I'm trying to piss in your wheaties. I'm just asking for those who are reading to ask and be informed.
The surface prep needs to be followed by the recommendation of the paint manufacture's p-sheet. As in "prep bare metal by sanding with 180 grit paper." Just need to make sure the media is giving an equivelant.