More Ospho/Rust Discussion

JimKueneman

Mopar Nut
On my A100 I am having a dilemma. It was sprayed with a foam on the interior of the cab for some reason (heat rejection in Phoenix?) and everywhere the foam was it absorbed water and pitted the metal under it. These parts are the backside of exterior panels so if I do what I should, blast the crap out of them to get all the rust out of the pits I will for sure warp the panels. Now that I have removed the foam, paint and wire brushed it I plan on hitting it lightly with the blaster (harder in the corners were there is support and more pitting) if I hit it with Ospho, neutralize it then epoxy it any bets on having issues in the future? These are areas that that should never see moisture ever again.

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I would blast it all and not worry about the Ospho. If you have a small blaster, essentially anything non commercial and cut the air pressure down to around 60'ish and adjust the material flow to match the lower air pressure, you can blast away and not ever have to worry about warping. Warping doesn't come from heat as it is often said, it comes from the material itself combined with air pressure. The weight of the material combined with the force (PSI) of the air is what causes warping. Small machines don't put out enough material to warp something in most cases. And even if yours does, cutting the pressure down to 60 or so will ensure that it doesn't. 60 psi will allow for a smaller amount of material to be properly atomized for blasting. So IMO it's pretty safe to do. If you do though make sure to test something beforehand just to be 100% sure.
 
I would blast it all and not worry about the Ospho. If you have a small blaster, essentially anything non commercial and cut the air pressure down to around 60'ish and adjust the material flow to match the lower air pressure, you can blast away and not ever have to worry about warping. Warping doesn't come from heat as it is often said, it comes from the material itself combined with air pressure. The weight of the material combined with the force (PSI) of the air is what causes warping. Small machines don't put out enough material to warp something in most cases. And even if yours does, cutting the pressure down to 60 or so will ensure that it doesn't. 60 psi will allow for a smaller amount of material to be properly atomized for blasting. So IMO it's pretty safe to do. If you do though make sure to test something beforehand just to be 100% sure.

Would you try to get ALL this black out even in the deep pits? That can take a lot of pressure sometimes to get that out.
 
Would you try to get ALL this black out even in the deep pits? That can take a lot of pressure sometimes to get that out.
Like I said above cut the pressure down to around 60'ish and blast away. I don't think it will be an issue. If you are concerned try doing a test on an area or test piece. I doubt that you have enough volume capability with your machine to actually warp a panel. Especially with the pressure cut down. Don't hammer one small spot make passes over an area and repeat. Use fresh media as well, after using both, personally I think crushed glass cuts better than coal slag.
Perhaps @shine can weigh in with his thoughts as well. I know he is an advocate of turning down the pressure.
 
Like I said above cut the pressure down to around 60'ish and blast away. I don't think it will be an issue. If you are concerned try doing a test on an area or test piece. I doubt that you have enough volume capability with your machine to actually warp a panel. Especially with the pressure cut down. Don't hammer one small spot make passes over an area and repeat. Use fresh media as well, after using both, personally I think crushed glass cuts better than coal slag.
Perhaps @shine can weigh in with his thoughts as well. I know he is an advocate of turning down the pressure.

I'll get a bag of glass today and do a comparison
 
I'll get a bag of glass today and do a comparison
I had always thought coal slag was more aggressive until I started using the crushed glass. In my experience crushed glass cuts faster, especially with rust, and gives a more aggressive "tooth".
 
I had always thought coal slag was more aggressive until I started using the crushed glass. In my experience crushed glass cuts faster, especially with rust, and gives a more aggressive "tooth".

I have had no luck with coal slag and rust pits. I use a mixture of slag and Starblast (I think Shine uses that too). The Starblast is fine and gets down into the pits and cuts very well. It also lasts a long time so it can be recycled a few times.
 
I have had no luck with coal slag and rust pits. I use a mixture of slag and Starblast (I think Shine uses that too). The Starblast is fine and gets down into the pits and cuts very well. It also lasts a long time so it can be recycled a few times.
Give the crushed glass a try, I think you'll like it. It does cut rust well.
 
I think the issue you may experience with neutralizing the Ospho is that any runoff is going to collect at the bottom and possibly cause adhesion issues there if you don’t get it all out. Exactly where you’d need the best epoxy protection. Not saying it wouldn’t work, but you may have to be more diligent in cleaning out runoff.
 
I'll get a bag of glass today and do a comparison
You have to make sure you're getting crushed glass, instead of glass beads. Beads are round as the name implies, and they are for polishing, such as for zinc plating. Glass also needs to be very low volumn while blasting, as in you can barely see them in the air stream.
 
You have to make sure you're getting crushed glass, instead of glass beads. Beads are round as the name implies, and they are for polishing, such as for zinc plating. Glass also needs to be very low volumn while blasting, as in you can barely see them in the air stream.

Yup. I use beads for aluminum and such. Got 1 medium and 1 coarse crushed glass. My Starblast is out of stock so I’m still waiting for that to come in.
 
I’m no expert but I use Harbor Freight glass bead all the time. I don’t have any issues blasting off paint and rust. I use the HF 110lb blaster usually set at 70psi. I’ve been able to reuse the beads numerous times, as well.
 
The trick for not warping panels when blasting is to increase the distance of the blaster to the panel, hold it at an angle to the panel and don’t try to remove all the material in one pass.
 
I’m no expert but I use Harbor Freight glass bead all the time. I don’t have any issues blasting off paint and rust. I use the HF 110lb blaster usually set at 70psi. I’ve been able to reuse the beads numerous times, as well.
Tha harbor freight glass beads are actually crushed glass. Look at the reviews on their site. They must have changed suppliers a few years back
 
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I had always thought coal slag was more aggressive until I started using the crushed glass. In my experience crushed glass cuts faster, especially with rust, and gives a more aggressive "tooth".
I agree with this and I have used both numerous times. Crushed class is the best choice and will get into those pits.
Shine also brings up a key point in spraying at an angle.
 
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