media blasting

[1958Warrior]

Looks good,color is dead on compared to the glove box,time will tell the durability.
I knew a guy that painted his truck with black rattle can paint , he wet sanded it and waxed it looked good for the time he had it about 5yrs.

[Krats1951]

So I went to the Paint Store to get primer for my recently glass blasted 58 and the guy there said that I should sand the whole thing after the blasting and before the primer because pieces of glass (sand) can get stuck and cause rust under the primer and paint later on. Anyone else heard of this problem?

I don't have much problem with humidity here in the banana belt of the NW, Boise, ID. So the parts that were blasted weeks ago have no rust and are in the garage.
I hope I post this correctly, New here

[roger55]

Originally Posted by Krats1951

So I went to the Paint Store to get primer for my recently glass blasted 58 and the guy there said that I should sand the whole thing after the blasting and before the primer because pieces of glass (sand) can get stuck and cause rust under the primer and paint later on. Anyone else heard of this problem?

I don't have much problem with humidity here in the banana belt of the NW, Boise, ID. So the parts that were blasted weeks ago have no rust and are in the garage.
I hope I post this correctly, New here

Don't take advice from anyone who works at a paint store. That is just crazy.

The bare does metal needs to be prepped for primer. Go by what the P sheet for the primer your using says to do.

I use SPI epoxy primer. Their instructions say to sand bare metal with 80 grit on a D/A and then clean with a waterborne w&g remover. But I have found that with blasting with the media I use, leaves an etched surface that works great without sanding. I've been using the coal slag product called Black Diamond. Black Beauty is the same stuff. Starblast is supposedly good stuff too.

[_Ogre]

we sand blasted truk, wiped it down with w&g remover and primed it with 2k primer 8 years ago and have no problems
i strongly suggest you get primer on your truck asap, surface rust has a way of just appearing

[Richs'55]

Originally Posted by roger55

Don't take advice from anyone who works at a paint store. That is just crazy.

Kind of a blanket statement there. Not necessarily true either.
I have painted 5 vehicle and have always taken the advice from my guy at the paint store (Arnold Motor Supply). It actually the only place to get auto paint in our town. He has been painting for almost 30 years and is very knowledgeable on current procedures and products. He basically walked me through the first paint job that I did and it looked pretty good. More my inexperience then bad info.

[roger55]

Yeah, I should have said most paint store people don't usually give good advice. But, there's always an exception. You might get lucky and find one that's got real experience. But, it pretty much is known that most don't.
Heard some pretty silly stuff from them and this is a good example.

[ptc]

I was quoted over $1100 to do a cab with doors, 2 front fenders, 2 inner panels, front support pieces, 2 bed side panels All on both sides. So thats basically 8 panels, some misc pieces and a cab inside and out is how they figure it.

I can rent a total self contained unit for $590 for a weekend, IF ANYBODY in my area (SACRAMENTO CA) is interested in splitting the cost of a Dustless Blaster for a weekend I'd be glad to set it up and go that route.

That doesnt include media, the glass media ia about $9 a bag and they say about 8 bags will do a whole car. So that about $100 with tax and stuff.

I know I can do my stuff in day - If someone wants to split the costs I will set it all up, you can do it at my place I have lots of land, no fuss no muss!

It will cost you $300 + Mat basically to do it all you can yourself in one day or so.

Let me know soon - Im gonna do this quick

[dwcsr]

Originally Posted by Krats1951

So I went to the Paint Store to get primer for my recently glass blasted 58 and the guy there said that I should sand the whole thing after the blasting and before the primer because pieces of glass (sand) can get stuck and cause rust under the primer and paint later on. Anyone else heard of this problem?

I don't have much problem with humidity here in the banana belt of the NW, Boise, ID. So the parts that were blasted weeks ago have no rust and are in the garage.
I hope I post this correctly, New here

The high end painter we sometime use says to sand it before priming for the very same reasons stated and it helps dislodge any media that has buried itself in the metal. We have also had the blaster prime it immediately after blasting without sanding. I haven't seen a difference in quality but I guess time will tell on the rust issue.

[roger55]

Originally Posted by dwcsr

The high end painter we sometime use says to sand it before priming for the very same reasons stated and it helps dislodge any media that has buried itself in the metal. We have also had the blaster prime it immediately after blasting without sanding. I haven't seen a difference in quality but I guess time will tell on the rust issue.

I'll argue with your "high end" painter all day long on that.
Sand DOES NOT imbed itself into sheetmetal with blasting. It just doesn't. It certainly does in cracks and seams though but sanding won't help that.

[dwcsr]

Originally Posted by roger55

I'll argue with your "high end" painter all day long on that.
Sand DOES NOT imbed itself into sheetmetal with blasting. It just doesn't. It certainly does in cracks and seams though but sanding won't help that.

I've seen it in leaded areas, bondo, and because of the process I have to believe it does. You take sand which is all sorts of materials from agate, corundum, quartz, flespar and silicon dioxide all much harder that metal. We take and blast that mixture into a rusty painted metal sheet at high velocity and tear off the paint, rust and a little metal and all the sand shatters on impact as it does this process. So I have to believe that it just doesn't fall off completely even with a wipe or two still it must have some embedded in the surface. I have seen 3 month primer job come in with rust under the primer. Bad prime job, poor prep? No idea but all were blasted and immediately primed.

I'm not a painter and I don't have to guarantee a paint job so I do what my painter asks for prep. If they want sanded after blasting and then primed that's what they get, If they want primed immediately after blasting that's what they get.

I'd be willing to bet that if you took a jewelers loop and looked at the panels after blasting you'd see some crystals in the metal.

[roger55]

I've been blasting and painting for over 30 years. Never seen it and never had issues.

Yes, media can be harder than metal. But it peens and bounces off.
Filler and lead are are a bunch softer so I can't argue there. I always remove all filler anyway. Sometimes I remove lead and sometimes not. But, I wouldn't blast it anyway because it tears it up. If I unintentionally hit lead with my blaster, yes I would sand it.

I know several pros who blast, wash and primer and have been doing it that way for years as I have.

I can't say that if the pressure was upped to a way high number it couldn't happen then. But who would try that anyway? The idea is to keep pressure no higher than necessary and blast at an angle to eliminate warping the metal when blasting in the middle of a panel. (probably not possible with the thin sheetmetal used in today's new cars). I usually only blast hard to get areas and D/A the rest. I don't see the need to blast the entire panel when it's easy to sand with a D/A even though I'm confident I can do it without warping the 18/19 gauge sheetmetal our older cars and trucks have. If there's several coats of paint I'm removing, I use the 4" paint stripper discs on a angle grinder. Removing paint with a blaster is much slower than that is. A least it is with my pot blaster. The paint stripper discs are a good way to go anyway. Use them with care and they will last quite a while. A whole car may take a dozen though so you want to get them from a supplier and not at a big-box store.

Anybody got a microscope capable of photos?
I'll take that wager.

[dwcsr]

Originally Posted by roger55

I've been blasting and painting for over 30 years. Never seen it and never had issues.

Yes, media can be harder than metal. But it peens and bounces off.
Filler and lead are are a bunch softer so I can't argue there. I always remove all filler anyway. Sometimes I remove lead and sometimes not. But, I wouldn't blast it anyway because it tears it up. If I unintentionally hit lead with my blaster, yes I would sand it.

I know several pros who blast, wash and primer and have been doing it that way for years as I have.

I can't say that if the pressure was upped to a way high number it couldn't happen then. But who would try that anyway? The idea is to keep pressure no higher than necessary and blast at an angle to eliminate warping the metal when blasting in the middle of a panel. (probably not possible with the thin sheetmetal used in today's new cars). I usually only blast hard to get areas and D/A the rest. I don't see the need to blast the entire panel when it's easy to sand with a D/A even though I'm confident I can do it without warping the 18/19 gauge sheetmetal our older cars and trucks have. If there's several coats of paint I'm removing, I use the 4" paint stripper discs on a angle grinder. Removing paint with a blaster is much slower than that is. A least it is with my pot blaster. The paint stripper discs are a good way to go anyway. Use them with care and they will last quite a while. A whole car may take a dozen though so you want to get them from a supplier and not at a big-box store.

Anybody got a microscope capable of photos?
I'll take that wager.

This says it can
http://www.ctgclean.com/tech-blog/20...tal-finishing/

This seems to indicate that the media can be embedded
http://www.osti.gov/scitech/biblio/912340

as does this one

http://www.moalohablasting.com/conve...omparison.html

I read some of the grit manufacturers literature they also seem to think or actually say it leaves embedded grit it the surface, Star-blast for one boasts
"Less embedded grit" left behind in the surface.

[roger55]

The first link is just a blog. Someones opinion. I don't give it any more credibility than any I would someone who make a post on a forum that says the believe it does embed.

The second looks like it was a study but the link you provide says nothing about embedding in the abstract and we can't get access to the full study. This one might have some credibility with real tests and real analyses but we don't have any idea if the issue is addressed in the full journal article or not.

The last link is from someone selling a product. Again no more credibility than anyone here (me included).

Again, we only want to know whether it happens with the actual type of blasting done with the removal of paint and rust from our old cars.

This is turning out to be a good discussion. I thought the idea was pretty crazy when first mentioned. Maybe not but I still don't believe it.

[roger55]

Just another note here that I think is important.

I doubt whether professionals in the classic car restoration area ever blast with sand. And shops that farm their blasting out wouldn't choose a company that would use sand either.
There are a few reasons not use sand.
First is that it's unhealthy from the free silica it releases. You don't want to be doing that in your yard even if you are wearing good protection. I don't know anything about regulations in using it in a business but I bet there are some.

Another reason is that it leaves a surface prone to rusting quickly. Much more so than using other media. I've been told the dust residue it leaves behind is acidic and that makes sense. Add the humidity to air to anything acid and it promotes corrosion and rust.

I've been using coal slag. It has virtually no free silica, is cheap and works well. I've let blasted parts set in my shop for a long time without cleaning other than blowing with air and it takes a couple of months before flash rust starts. I started liking it so much with my pot blaster and liked so much I tried it in my cabinet and have been using it there since. I was using glass beads. I switch back to glass beads for aluminum blasting however. I can't get washed coal slag anymore here locally and been buying the unwashed. Works fine for the pot blaster but I won't put that in my cabinet.

[Krats1951]

I am glad I asked the ? I thought for sure the paint seller was full of it. It is very interesting to hear both sides. But I'm still not sure which is right or if both are. I am not sure I was clear about what media was used (recycled glass) even so it still seems to be a debate. I do value the opinions of what I think are more experienced gear heads then me. Thanks again

[roger55]

Let's assume that there are some embedded particles. I don't believe that there are but just for the sake of applying further logic, lets say there are.

If the left behind particles don't contain moisture or an acidic content, then epoxy primer will seal them in with absolutely no harm. I can say this because the all the pros I know in the classic car restoration business blast, blow, wash and epoxy primer. They wash with soap and water and then waterborne w&g remover. Some don't wash and just use the waterborne w&g remover only. I've done it both ways and never had a problem with adhesion. The favorite soap to use is Dawn.

If someone brought a metal part to me where sand was used to blast it, I would re-blast or sand it. Automotive Epoxy primer doesn't like acid. The SPI I use is very clear about this. For that reason they are very specific about soda blasting and it is highly advised not to use it. Too hard to get it all neutralized properly. The pros I know won't touch a job when a customer brings a car that has been soda blasted.

I've blasted with crushed glass and glass beads many, many times and never any problem.

[tmoble]

I recently had my cab and doors wet blasted with ground glass. They came to my house and did it in the driveway. They warned me the sand would be packed into places where it would be hard to get out and they were right. I eventually cut windows into the sides of the cowl/firewall panels to get in there. I bought long pieces of copper tubing to mount to my air guns to blow in some of the places. It was a PITA and took a couple days with my 18 year old son helping. We vacuumed the glass to avoid chasing it around from place to place blowing. it's a 57 BBW cab, bad spots were between the inner and outer roof panels, between the inner and our rear panels behind the gas tank, under the dash and in the big cowl side pockets where I had to cut windows.

Big warning: the commercial dustless/wet blasters use a chemical in the water to stop flash rust. It's called Hold-Tite or something like that. I wouldn't touch wet blasting without it.

One good thing was the Hold-Tite treatment lasted much longer than the 48 hours promised. That's here in Phx area where it's humid this time of year.

the wet glass does pack into areas like wet sand at a beach between rocks. I had them essentially rinse the cab with their pressure rig with the water/Hold-Tite chemical mix and no glass but it didn't help much.

The process blows paint off in a hurry, but I held them on the job much longer to get in all the nooks and crannies of the cab. They charge $250 to show up and one hour. $225/hr after that. They were there 4 hours, not a cheap deal. But, the Omni epoxy primer I used (MP175/170) sticks like crazy to the toothy surface left behind. No adhesion issues at all but I use a DA with 80 grit to dust off the surface. I wiped the unsanded surface with a clean rag and thinner and it left lint-like stuff everywhere. had to sand it off.

[BIGglaSS]

How about aluminum oxide? I doubt any particles left behind would cause a problem. I had a core support blasted with aluminum oxide. The blaster said he wont do body panels for liability of warping. I like Roger's idea of DA on the panels, and blast the jambs.

Blasted with aluminum oxide, I gave it a quick scrub with scotch-brite, and no grit came off. I know it was handled with bare hands, so I wiped it down with wax and grease remover. Then sprayed 2 coats of SPI epoxy.

[roger55]

Aluminum oxide is great stuff and works well. I found it on the expensive side though and the coal slag works just as well.