Sand blasting

Have some questions about sand blasting

We have access to a large-ish industrial sand blasting doohickie

I was told by the fella that owns it that depending on what you use to blast with depends on how smooth the outcome will be

If to course a material is used it will leave a rough finish
If a fine material will be used it will take a long time blast clean

So does anyone have any experience with sand blasting?

If so what materials achieve a good result for a surface to paint right over and a good and smooth result so I wont have to prime

Apparently I can purchase paint mixed to my desired colour to go straight on

Any thoughts on this are appreciated

Paul

What little I know , the bloke that did a truck for me said , he uses crushed garnet , but is suposed to be expensive. Should be plenty of work for one , should keep an old cane farmer busy !

Paul

When I had my marine construction business we had to sandblast on every job.

The industry and government standard called for Ilmenite (black mineral sand). All the steel piles and structures had to be done to a finish standard. The Ilmenite produced a lovely grey keying surface without aggressive surface pitting. Great for cars etc. We immediately coated with two pack epoxy tar and the piles lasted ten years before reblasting.

Ilmenite is easy to handle although it runs like water so plug up any tiny holes in your truck or trailer. Best to buy in bags not bulk. It produces less dust (still lots) than many mediums although you should still wear a pressure helmet. It is extremely hard with sharp cutting edges and can be swept up. sieved and reused many times. It is heavy so the hitting energy of the grains is very effective.

There are many things you can use for specialist jobs but Ilmenite is hard to beat as an all-rounder. Beach sand works well apart from the high dust level as the soft single use grains smash themselves on impact. If you ignored the fact it is illegal to use, working with it every day would probably put you in the grave with silicosis

Don't forget that rust is OK but the old paint you are turning to powder and dust may contain lead or asbestos - keep that helmet on.


Lang

PS Sandblasting is about the worst possible thing for your hearing. The huge noise right across the most susceptible frequency range is a very serious danger. You MUST use hearing protection any time the hose is running regardless of whether the sand tap is on or off. This includes helpers or watchers nearby.

Here is the National Workplace Safety Standard blasting advice
The following materials will not usually result in exposures greater than national exposure standards. However, you should check the Safety Data Sheet to ensure the composition of substances does not exceed prohibited levels
⦁ ilmenite
⦁ aluminium oxide
⦁ garnet (low crystalline silica content only)
⦁ other rocks and mineral sands which do not contain significant levels of silica
⦁ metal shot
⦁ steel grit
⦁ crushed glass
⦁ sodium bicarbonate
⦁ plastic beads
⦁ glass beads
⦁ some metal slags (check content analysis before purchase)
⦁ dry ice
Note: There are environmental requirements in relation to abrasive blasting mediums. If in doubt, seek advice from your local council.

The surface finish provides a key for paint,and for a high build two pack one coat system ,you need a coarse finish or the strong two pack coat will come off in parts........IMHO ,single coat paints arent a good idea for vehicles ,as any danage to the coat lets water in and the metal will diintegrate with rust............I base this on the sandblasters trucks ,and the amount of rust in them,,and also the damage to powdercoat panels when water penetrates the coat.

Another point ,if you have a lot of air -say 400cfm+,then be careful you dont burn or hesat distort sheet metal.........I recall one guy left a Holden one tonner bonnet and the front off an XJ6,....needless to say ,they were given to a beginner to blast ,and the Jag bonnet actually got a long cut in it ....they are alloy.......the Holden was all buckled ,and the owner accused the blaster of standing on it....but it was actually heat distortion.......Dont ask about the VW they rolled over on its roof to blast the underside.......Or all the xrayed fabrication they busted ,and I had to repair (so much for the xrays).....One time they did heavy pipes for the Gladstone LP plant ,and broke off a heap of little 1" bleed pipes........I had to weld them all back on again.

Ilmenite is a very dense material. We used to cart heaps of it from Capel - near Bunbury - to Fremantle. A 2t bulker bag only stands about 3 ft high.
A combination of a new truck driver, new forkie meant about 80 t on a 10 axle B double - was the only day in a fortnight the scalies weren't at the Freo Wharf. The Boss was more than a bit angry until we pointed out the lack of training given to the driver. No harm done, saved money !!!
Cheers, Neil.

Lang is rightg on the money with the best type of abrasive. When I had the David Brown blasted it was wet blasted and they also put an anti-corrosion acid in the water mix to slow down the surface rust. He used what looked like crushed glass on the tractor tin ware and was a bit harsh but IK did have to do a bit of body work and filling so it was a bonus to me. He changed over to something less coarse when he was doing the alloy parts like the top of the gearbox and bell housing.
I certainly would not go to this amount of trouble and not give an undercoat or a metal primer before top coating goes on. Remeber you will be spending a lot of time blasting and will leave very little time to paint unless you have a crew working with you.
I have a small blasting cabinet and originally I had Garnet in it and it really strips paint off quickly and was not as agressive as the crushed glass used in the wet blaster. Now I am using glass beads and is gentler on all the metals and even leaves alloys a bit shiney.

Thanks for the replies everyone, some food for thought

I'll do some more investergation into this, as in what compressors are available to higher and the cost of mediums to blast with

And some safety asspects, as in it's effects on me as I have never tackled anthying like this and as always it will be a steep learning curve if I decide to go ahead with sandblasting


Paul

cobbadog wrote: I certainly would not go to this amount of trouble and not give an undercoat or a metal primer before top coating goes on.

Thats a interesting thought, Caterpillar have not used primer for well over 60 years that I know of and there is still plenty of old bangers around with yellow paint on

Mind you they have no doubt been repainted a few times by now
I will look into this further


Paul

Paul

99% of general sandblasting will go well with 200/250 cu ft compressor. This will need 100 to 120 hp. Should be able to find an old Perkins or Ford diesel powered one at the right price. Screw compressor is many times better than piston type. All about the nozzle size so if it starts to lag behind replace the tip or if you get hoses from somewhere with wrong tip size just experiment. Ceramic tips are not expensive.

Talking about tips, never ever just shovel the used sand off the floor into the pot for another run. Always use a sieve to clean it. For Ilmenite a square box with common fly screen bottom is perfect. Dirty sand (paint and rust chips or dirt and grease lumps) will drive you insane.

Lang