Sand/bead blasting DIY?

[3xpendable]

I'm currently tackling repairs to the front wings on my MGB, which are pretty solid but have areas mainly on the front end with many pin sized bubbles. I have gone down to bare metal using a carbide disc (its like a grinder but softer, it just removes paint) and in some areas there is still dark pitting that obviously needs to be removed.

I decided to DIY sandblast the small areas using fine dried building sand and a blasting gun my dad has. I'm pretty pleased with the results except that for some of the rustier sections it hasn't seemed to remove all the rust. You have the typical post blasted grey dimply surface but I can still see some tiny areas of orange (rust). I repeated the blasting on these areas a couple of times but no improvement. There doesn't seem to be any mobile blasting services nearby so i'm a bit stuck, any ideas? Am I being picky?

Thanks

[tractorman]

Apart from being nasty stuff (the Silicon isn't good for you), ordinary sand is too fine and soft for blasting. Aluminium Oxide is better at removing rust - coarser grades are most effective. "Shot" is a more aggressive version. One reason why I don't do more blasting is the price of the media in comparison to sanding discs etc. Even if you have a cabinet, the reusable stuff only lasts a couple of sessions (and is a lot more expensive).

[3xpendable]

Good point tractorman, and thank you. So do you suggest just grinding down until i'm to clean metal?

[jimmyybob]

Using sand is in fact now illegal.

AB grade glass bead will get rid of the black marks and leave a smooth bright finish but without a cabinet its all just expensive waste, glass is about £1 a kilo and a kilo will last about 15 seconds in my machine.

[3xpendable]

I take It you mean for commercial applications Jimmy? I mean the police won't be kicking down my door if I use it in my back yard?

That's the problem, do I pay someone to do them or fork out for the media and get covered in it while blasting?!

[tractorman]

It depends on how much rust there is - it may be better to use something a little more aggressive in the angle grinder or use some chemical rust remover/converter. One problem with blasting is that enthusiastic use with coarse media can distort the panels (it heats them up); the upside is that a good blasted finish gives a better surface for etch primer to grip/eat into: I think this is the finish you were expecting!

Glass is great for a nice finish on aluminium (eg inlet manifolds carb bodies etc), but I don't think I'd use it on something I was intending to cover with paint. I'd go for something like garnet or other dispensable stuff - check eBay, there are some good options there, even if carriage is a killer!

[3xpendable]

Thanks Tractorman, someone is doing 25kg of Garnet on eBay for £20 all in, so i'll get some of that!

Here is the worst wing, obviously the light parts are where I've grinded/blasted

[tractorman]

To be honest, if that's the worst of the rust, you are lucky! I've treated worse stuff than that with rust remover and a good etch primer and had no problems with rust returning! However, I think you're probably on the right lines - get it as clean as you can and then etch prime it and will probably be as good as new!