I heard from someone that if you don't sand your panels after sandblasting them, that your paint will eventually peel off because the Silica gets imbedded in the sheet metal. I personally think this is obsurd, but I would like to get your guys' opinion on this. I do know that whenever you sodablast something, that it leaves a thin film which must be removed, or your paint will peel. However, I never heard of this "myth" about silica peeling your paint eventually (after sandblasting) until today. Is it true?
wow i hope not lol sand blasted my wheels 11 years ago and just painted them spray can black but they held up fine still good today...not sure about body panels tho
That's just not right. Sandblast them and then treat them like any other sheetmetal for paint prep etc.
I do know that ACID washing after sand blasting, is BAD MOJO, the acid gets down into the pores and creates rust worse that before. I have witnessed that first hand. However, sanding will help knock the high spots down on the sandblasted metal, and need less primer to become smooth.
http://www.jalopyjournal.com/forum/showthread.php?t=565336 Not exactly related to this question, but there are some grains of wisdom in the above thread that you might find relevant to this discussion.
Some finishes are not designed to go over blast profile. It depends on what you are spraying. Most paint manufactures (I deal almost exclusively with PPG) will tell you to sand after blasting. You end up with peaks in the metal, which will affect adhesion. They make an epoxy that can go over blast profile, ESU470 (which is a fleet finish epoxy) or the DPLF, or DPLV series epoxies which should e sanded before spraying. Again, just depends. When in doubt, always read the product info sheet!
After I had my body sandblasted, I ran over it with a grinder and scotch brite disc to clean everything up before etch priming it. Body has been that way for a few years now. Eventually I'll get around to finishing the bodywork and prepping it for paint. Only a few dents and some rust.
i've heard body guys on both sides... one side says "just use a decent epoxy and you're good to go" the other says "sand it down or else" personally, i'd think that after most blasting if it needed it is going to be sanded down anyhow after metalwork. i'm not a huge fan of blasting panels anyhow... too easy to end up with wavy warped body parts, and then even more work to get em right... i use a DA and/or chemical strippers to get down to bare metal when i need to
I have run into this issue that stinger12 is asking about, but it is on woodstoves we found that the silica will stay in the casting and to get it out your either have to steel wool everything and clean with thinner, or clean it and run some heat through the stove until the smell stops than paint it once cooled down. Unless thats down the paint would flake off in huge sheets and only the areas that where sandblasted.
its always good practice to "knock down" the profile made in the steel from Media Blasting before painting..scotch brite or 220 sand paper anything to smooth it up a bit , if it removes a contaminate from the face of the steel , than its just a bonus..I always knock down the profile on any part i sand blast that im going to paint, unless i want the rough profile if i want the rough profile, i wipe the part down with a good grease and wax remover before painting, as I do that with anything painted anyways
I have heard that is a problem with soda blasting not sand blasting if the surface is not washed afterwards. Proper surface prep for any coating does not end with blasting the metal. At the minimum I would wipe it down with one of the bare metal prep products such as Prep Step (Zero Rust product) and/or a degreaser.
von rigg has the right idea. when you sand blast some of the grit gets embeded in the metal. just run your had over a sand blasted area and feel how rough it is. then rub it with some 180 or so then feel the differance. no one should use silica sand its very bad for you.
I sandblasted my 30 pickup and painted it 12 years ago with no problems yet, a friend of mine had a 56 Nomad media blasted, washed it with metal prep and used epoxy primer and the paint peeled off in sheets after about six months. I think you should scuff it after blasting of any kind to remove any residue and give the primer a little bite.
There is a guy in our town that is a restoration perfectionist. I have personaly seen some of his work and his metal work, before paint, is absolutly amazing. He does the metal finishing as if he was not going to paint it. He does use filler but only the smallest, thinest, coat possible. My whole point is He sands all possible surfaces at 220 grit to prep and clean. He said, as the OP, that after sand blasting and other types of blasting that there is left over contaminants on the metal. I guess this could be talked over-n-over but I can not argue his results. The product he turns out speaks for it's self.
Well this does raise a question because silica sand has been banned for use on anything because of silicosis, a nasty lung problem that can kill you. My blaster uses black beauty or sifted beach/play sand. I have not had any problems, I also use PPG, but I use the CRE high build primer, seems to really lay out nice on blasted stuff.
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