• Having site issues? Contact Dub@southernPolyurethanes.com

Flash rust, or something like else?

#1
I had this car blasted with the dustless blasting system. Now, there are some spots on the metal that seem like they are stained. Sanding with a da and 80 grit doesn't seem to touch it. Not sure if it's something to worry about, and if/how to get rid of it.
 

jlcustomz

evil painter
#2
The dustless system is still relatively new & many of us haven't in person seen a vehicle done yet. Closest person near me last year told me about $2000 & didn't sound too experienced when I asked a few questions, so no way for me. Also heard lots of complaints about warping.

​Anyways, best I can make out from the pic, looks like rust leeching from some of the metal's pores. I'd try hitting it with a rotary wire brush wheel rather than trying to sand out.
 
#4
I really do not get the allure of the dustless blasting system. Its a slurry of water and baking soda in most places. The light brown is flash rust from drops of water on the freshly blasted surface, but the rest of the darker areas are areas of rust that were not removed completely either.
 
#5
Thanks for the tips. The wire wheel does help get more of it off, that the sanding wouldn't touch. I will try the naval jelly next. Only thing I can think of is that some of the salts from the blasting or whatever caused this. However, its almost like a stain, or like a dye in cloth, as its not raised or anything.

Regarding dustless blasting, after the experience, I would favor traditional blasting over dustless as there is less issues with contamination from the water blasting residue. Also much more work to clean it up inside the car. However, it does have the advantage of limiting dust which can be important in a more residential setting. From my understanding, they do not add baking soda, but a product called hold-tite, which is a wetting agent that allows the water to flow off and not linger causing rust. Now, I had my car done in 40 degree weather, so the water lingered longer than on a summer day which is probably part of the problem. Anyway, I will be glad to share any other info on the process from my experience.

​Thanks,

Chris
 
#6
I bought regular baking soda from my chemical supplier to try to use in the soda blast pot and it was all clumped up and unusable. the baking soda explodes when it hits the surface and the explosion knocks off more paint than just the bead of soda hitting it. So I was told this is what they use in the dustless systems. I think hold tite is just an additive for the water, they might not have had enough. Any caustic is going to not allow the steel to rust, so its simply keeping the ph well above 7 that does not cause immediate rusting.
 
#7
most dustless rigs use crushed glass. any soda will do a piss poor job on anything other than paint. look for a moh rating of at least 3.0
 
#8
I'm sure they have to add more of something in the mix, since baking soda has no power against rust anyway, At least the last time I saw a dustless trailer in my area, I see the trailers blasting and the water slurry running right down storm drains, I dont think they could do that with glass. Honestly, I did not think they should have been doing it at all.
 
#9
as shine said there is no baking soda in the dustless system at all. if it was they damn sure would be out of business because its pretty widely known now that soda is a no no. they used crushed recycled glass mixed with water and holdtite to stop the flash rust. crushed glass is a green media and supposed to approved near waterways etc. now what its blasting off is another story but the media itself is silica free and basically inert. we have multiple guys here in the area doing it. i have had 2 of them blast stuff for me. its all the same setup. only thing different is the guy in the suit.
 
#10
I've looked into the Dustless systems. I'd have to keep my current rig for winter blasting and I can't imagine trying to clean up the sludge that is going to run down into the cracks that a normal shop vac and some spinning on the rottisserie get rid of.

Cwlo - What is the worst part of your cleanup on the job?

I've never blasted with glass bead other than the cabinet and even then it's just for hardware replating. What glass grit is recommended for sheet metal?
 
#11
Brad J.;n80923 said:
I've looked into the Dustless systems. I'd have to keep my current rig for winter blasting and I can't imagine trying to clean up the sludge that is going to run down into the cracks that a normal shop vac and some spinning on the rottisserie get rid of.

Cwlo - What is the worst part of your cleanup on the job?

I've never blasted with glass bead other than the cabinet and even then it's just for hardware replating. What glass grit is recommended for sheet metal?

I am pretty sure its crushed glass since glass bead does not do much for rust. I usually start with crushed glass because eventually you end up with glass dust that is pretty close to glass bead which is more expensive to start with. Crushed or ground glass starts about 25 to around 40 mesh, around 38 grit
 
#12
The glass bead in the cabinet does a pretty efficient job of removing rust from fasteners, door latches, etc.

Stuff I use says "Mil spec 8 70/100" on the bag. I just think it's do fine for bodywork. And to expensive without reclaiming it.
 
#13
i reclaim star blast and cycle it until it is powder . 50 lb at around 10 bucks . thanks to the morons in washington i can no longer get olivine .
 
#14
So in my case, and im pretty sure with most dustless blasting, its crushed glass mixed with water+holdtite. As far as cleanup, it was a bit of work in the trunk and inside particularly, because there is nowhere for the water and glass to go. Once the water is dried out, the crushed glass is clumped together and will require a brush to break free before vacuuming/sweeping. It will linger more durably than regular sandblasting, since its clumped together from the water. Now, they really use very little water with the blast, but it does build up in the enclosed spaces.
 
#15
Now I wire wheeled it today, and it took the redness of the rust out, but the marks are still faintly visible. I'm thinking its good to go, but am curious to see if the naval jelly will have different results, and will try next. I'm just a bit hesitant due to the added issues of potential contamination.
 
#17
Holdtite 102 is an additive mixed in the water supply to reduce or possibly stop flash rust, but the metal still has to be coated within a short time frame, and that may be the problem for the OP. I talked to the manufacturer and he said it must be used with a pressure washer while blasting and during the pressure rinse. It works by completely deep cleaning the metal of all contaminates, which apparently is the key. It requires the pressure to work properly.

It is mostly associated with soda blasting, but all the dustless blasters are suppose to use it as well. Some of them may not be using the proper ratio though.
 
#18
Chevman has some interesting points. My car was blasted in colder weather.....about 40 degrees. He started in the morning, and in the afternoon was getting close to completion. At that time, there was some flash rust on the panels. It looked like it might rain, and the blaster was delayed due to running out of fuel so I opted to trailer the car home. Now, he offered to wash down the car, but I passed on it, figuring it would worsen the flash rust. Perhaps that was the wrong decision, but hard to tell, as the flash rust was already there.
 
#19
I think the areas most initially prone to rust already showed themselves & even with a color difference after wire brushing, should be ok getting a good epoxy sealing soon.
 
Top