Anybody know sandblasting?

Old 07-14-2018, 07:49 AM
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Default Anybody know sandblasting?

I'm trying to transition into commercial painting specializing in the horse farms around central KY and my first job involves taking down 11 heavy metal powder coated horse stall doors that have gotten somewhat rusted, sandblasting them then painting. I've done a lot of stuff but sandblasting isn't one of them. So I'm wondering just how does someone like me go about doing something like this. Do equipment rental places carry stuff like this? Other than handling the doors which I've got help for, is this blasting job something your average motivated joe can tackle?

Also, was wondering what'd be the best environment to get it done. The doors are installed in an all wood stable, and although a horse stall sounds like the ideal place to lean these gates up and blast away, I'd be afraid the wood wall behind it would disintegrate. There's another stable nearby that's made of cinder block which I imagine would make for a better staging area. These stalls are about 13 ft square which seems ideal for keeping the all the sand contained. I'm sure the wall would need repainting after everything was finished, but would a cinder block wall generally stand up to being hit with lots of sand?
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Old 07-15-2018, 10:19 AM
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I can't help out, but i'm curious. Commercial painting, to me, involves alot of sandblasting to do it properly. Was this not thought through? Or am i wrong in thinking sandblasting isnt as frequent as i'm thinking?
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Old 07-15-2018, 12:38 PM
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There are different medias for different types of blasting. I would read up on them before jumping in if its your first time. Using the wrong media can do more harm than good. Which one you use depends on what youre working with. Sand blasting is one method. Soda blasting is another. And dont forget the safety gear. You dont want high pressure forcing anything under the skin. That can get ugly.
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Old 07-15-2018, 04:46 PM
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My only exposure to sand blasting was watching a guy do the body of a 36 Plymouth in a field. He also said it's important to choose the right grit size so as the not to destroy the metal. He did the underneath part first by laying it over gently on it's side in the weeds, then putting it up on pallets to do the rest. He was dressed in full leathers with a face shield and heavy gloves. He told my friend he wanted a field where animals didn't graze so he could leave the sand there with all the paint chips and rust. He could have done it in a barn, but it was a lot cheaper if he didn't have to clean up after doing it. He did the frame separately in the same place.

I've had some experience with glass blasting heavy steel pieces. Glass doesn't change the metal surfaces, just removes the rust. It's more hazardous because you don't want to inhale THAT stuff!

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Old 07-29-2018, 09:44 AM
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The problem with powder coating when the metal begins to rust beneath it is the difficulty getting it removed. Getting all the exposed rust off is the easy part and shouldn't take much using standard glass bead. But, the enameled coating is on there permanent party because it's basically powdered glass bonded to the metal substrate by heat (it melts into the surface porosity). Getting it off requires a different blast media that could blow through the rusted areas where the powder coating has already flaked off.

Once rust gets out of hand it creeps under any coatings, like a powdered coating, and continues to rust the metal beneath. You can't see most of it. Creeping (propagation) will show under paint and appear like creeping vines. Powder coating, however, is very rigid and won't lift or "indicate" like paint does as corrosion propagates beneath it. It will just flake off at the very edge and continue to do that. You have to remove the coating back far enough to expose clean metal that has no effects of corrosion and then apply a protectant, like LPS3, to keep it free of corrosion as you continue to blast the rest of the piece. It's a huge undertaking in time and blast media investment.

Aluminum oxide comes if many different screen sizes (that's the way blast media is sized), or "grit". What will work well on one surface may damage another so constant attention to directing the blasting is needed, and masking off areas needing protection from it is advisable.

Probably the best first stage would be grinding all the edges of the powder coating where corrosion is present. Once the powder coating has been removed back to clean metal, blasting will be easy and fast with glass media. Then, I would suggest a deep cleaning of the newly exposed metal - probably showing much corrosion pitting - with a rust cleaner immediately followed by a good rust inhibiting primer. On surfaces like that where the surface aesthetics are inconsequential I cover with fiberglass cloth and polyester resin. It stinks pretty bad but of all the resins out there it's probably the best for environmental protection.

I just blasted the floor boards of an XJ with aluminum oxide. I took the blasting gun and slipped it into the spout of a funnel I resized to accept it's outer diameter. Then I cut a hole in the side of the funnel large enough to accept the hose of a shop vacuum. With the large end of the funnel held against the floor board I pulled the gun trigger and began the blasting as the vacuum recovered the media. It worked very well and at no time was there any free-flying blast media to deal with. The jeep is a side project for my son. He's getting the Jeep when done (his nickle funding the project). The funnel idea is not mine and there's actually commercially available products already marketed. I'm an aircraft mechanic and I've used them to strip polyurethane finishes from aircraft. But, I'm also cheap so the funnel is just a copy-cat dime store lash-up that works.

I'd call the maker of the stalls and ask them to suggest a repair. It may surprise you to learn your cost to repair versus their cost to replace might make replacing the cheaper option.
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