Hi Guys
I need advice. How do I know when sand blasting was done wrong? I got my son's bicycle frame sand blasted to get it ready for painting. It was previously powder coated. It has a slightly rough feeling to it and the guy painting it for me said he will have to use a filling primer due to it being so rough. I inspected the welding of the frame and you can still see the flow of the welding when it was welded.Logic tells me that if it was done too long or was done with a very coarse material the welding would not look like welding anymore due to the sand or whatever was used eating away allot of the metal.
It is a metal frame.Not aluminum.

from all of the cars that i have had blasted they have always had a fairly course finish to them when done. but the coats of primer and paint are normally enough to get it looking good. They have normally had the texture of say 800-1200 wet and dry paper.. if that makes sense

Ah. Makes me feel a little better now. How I can compare mine is if you look at the plastic surround of these 14" or 15" computer screens, you will see the plastic has a little rough texture. This is exactly how the frame looks when I got it from the blaster.

That is fine.

Soda Blasting is much more delicate.

But yes a high solids, high build primer would be the way to go.

I ran the sand-blasting plant when I was in PNG and experimented with all sorts of material grades. I found, re-using second hand material that had already undergone one or two rounds of blasting left a finer 'cut' on the surface.

Some hardcore abrasive material will literally, shred the top layer of the steel and leave a sharkskin finish. I guess you could have had it shot blasted which is a slight smoother finish but it's a lot more expensive (and more dangerous at that scale?).

When you want to see how well it was done look at how warped some of the panels are. As for a bicycle frame, it would take a very unintelligent person to stuff that up.... and even then it's pretty hard to do. I guess all you could criticize would be the grade of the material blast.

Thanks for the reply guys. Makes me feel a little better now. Clyons8, I have a idea they might be reusing the sand that has been used before to get max production out of the consumables.

yeah clyon is right, there are many different blasting grits you can get, some you can re-use and some you can't.

Garnet can be re used a couple of times before it looses its 'edge', when its fresh it leaves a rough finish, but primer and paint fills it well. We mainly use it for stainless steel jobs, but can be used on anything.

Black slag(blast furnace slag) is really rough and can only be used once not as good of a finish but is very cheap.

Stauralite(combination of the two above) is another product that we use at work most of the time for mild steel applications.

depends on the size of the blast hopper as well, we use a portable blast hopper, informally known as the 'mighty mite' doesn't blast anywhere as good as the 'big hopper in the workshop, the 'big boy' uses a 2inch bull hose, so you have to hang on!!!

Its all good! thats sound right, it should come up good.

when its gon rong on bicycle tubeing (to much in one place) you get a sort of 'pitting' effect

Powdercoating is often used where finishes are a little rough - it tends to fill imperfections but even then doesn't give a 'perfect' finish.

On smaller gauge metal I wouldn't sandblast, personally. I'd look at soda blasting, etc instead.