Tips on media-/sand-blasting

I've got a few small rust spots I need to tackle before winter, and I've got one of those little self-recycling mini-blasters (cheap little thing I bought at Tractor Supply), but I've never used it. I have two types of media: walnut shells and some sort of black grit (coal slag?). Any guidance on how best to proceed? Which media is the better option? Any other equipment I need? How much air pressure should I run (there may have been instructions with this at one point, but they're long gone)?

I'm figuring on clearing the rust, then etch-priming, filling, priming again, and painting.

If your considering blasting, I assume you have a decent sized compressor. For small rust repair I would not even bother pulling out the blaster.

For small stuff I buy these little 3M flap wheels and put them on my die grinder. They clear off anything and are much more precise with you work than a blaster would ever be. Not to mention the cleanup; is minimal.

NordicSaab wrote: If your considering blasting, I assume you have a decent sized compressor. For small rust repair I would not even bother pulling out the blaster. For small stuff I buy these little 3M flap wheels and put them on my die grinder. They clear off anything and are much more precise with you work than a blaster would ever be. Not to mention the cleanup; is minimal.

I've heard these recommended too: I'm going to try one myself soon.

The discs will work, but they are hard to get into cavities and cracks. A small media blaster works best. If you don't get every single bit of the rust out, at lest encapsulate it with POR 15 or something similar.

I've used the discs before, with good results, so I'll get some of those for the flatter, more accessible areas.

I'm still interested in advice on best practices for the blaster, as I suspect there may be some areas where it will be superior.

Either could work fine. I would use the black slag if you already have some. Walnuts aren't great at removing rust. I tend to treat any stripped areas of metal with an acid etching chemical to eat the rust out of the tiny pits, like Tim said.

The black grit is probably black oxide, which I believe is a medium grit media. I use that for a majority of the work in my blasting cabinet and probably very effective for your needs. Walnut shells are very soft and not very good at removing hardened paint and rust. The safest way is to try walnut shells first and then switch to the oxide if it doesn't do what you want it to.

My Harbor Freight blast cabinet works best at 60 psi BTW.

Yup, walnut shells don't do the best at rust or heavy corrosion (on Al parts)- but they are quite good at getting paint off of things like wheels. I've got black oxide, but haven't had occasion to use it on anything yet. I've gotten a lot of good use out of the glass bead abrasive media from HF in my HF blast cabinet- takes off a LOT more gunk than the walnut shells.

Glass bead would be my go to as black slag product can remove the base metal but in a small blaster like you have it should not be a problem at all. as others said walnut is to soft for rust / paint, save it for exhaust ports on what ever motor you have that has run on problems.

Oh the small self recycle blaster works down to 40psi but the high the psi the faster and deeper it works. you'll only need a small tank compressor to use one as you stop pull off the surface check then move over 2 inches press against surface and blast.

The coal slag will remove the rust, but it will texture the metal, so be aware of that. I'll echo the 60 psi thing. I was running at 110 psi or a while and the compressor was cycling a lot. So I started reducing pressure to reduce the duty cycle of the compressor and I found 60 was as low as I could go without seeing a loss of performance.

I have a small hand held gravity fed blast gun that I like.

I can only add two things to what others have said.

I use a funnel that is cut down that I put against what I am blasting then blast the area in the funnel. This helps contain the mess and the bounce back. The other tip is get a full face mask. A cheap one will do. Bounce back hurts and it will get in your eyes at some point.

Also a respirator if your open air blasting. Dunno about yours but ive got a tub of black slag and its got a HUGE yellow cancer warning label. Its not good stuff to breathe if you can imagine and you cant help to breathe it without a respirator.

I've got a 3M respirator that I was planning to wear regardless, so no worries there. Need to pick up a face shield.

My blaster has a rubber tip that's shaped like an inverted funnel, which should contain the media reasonably well.

I'll do some testing on scrap metal before I start, but 60psi sounds like a winner.

Thanks for the assistance.

In reply to 02Pilot:

I have the same blaster. I found that the rubber tip doesn't work very well and you can't see what you're working on. I use some cheap glass bead from HF. It does a decent job but for larger areas I found a wheel like above to be faster and easier to use.