TheSamba.com :: View topic - Cautionary Tale: sand blasting / bead blasting on body panel

Tue Jan 01, 2013 9:12 pm

Ian wrote: type241 wrote: I want to see some PROCESS pics on the hail damage. That is very impressive work. That would have been a ragtop graft for sure.

I agree, the work looks amazing.
Thank you!...yeah, I try to take as many pics as I can. But being a one man shop and restoring 6 cars at the moment....well.....

Tue Jan 01, 2013 9:53 pm

baxsie wrote: 543fold wrote: baxsie wrote: Can damage from a blaster be fixed? Sure it can!...I fixed some pretty heavy blasting damage along with hail and various other damage on a customers bug. :D
Wow, that body work looks fantastic! Do you want to come to Spokane for a week this summer and work on Kick Azz?

Your pictures obviously show that this kind of damage can be repaired (and quite well, I might add). My argument is that once the original stress that gives the part its original shape, springiness and "memory" is lost, and the part's metal now has different characteristics. The only way to test it would be to take a part that had been sandblasted heavily then expertly worked back into shape like 543fold did to those panels, and then (destructively) compare the re-worked part's memory and springiness against a factory panel.
I would love to come to Spokane and help you out! But you know.....

True! Metal does have a memory and can be worked back to its original form. It just depends on how BADLY the metal is damaged.

Fri Jan 04, 2013 12:45 am

Live and learn brother! Thanks for sharing your experience. It's one thing to 'hear' of someone doing it, it's alot more important to hear first hand experience.

We all learn from our mistakes! Good to know I'm not the only one who screws up :)

I obliterated a nice 55 Oval back in the day. I thought I was getting a bargain on sandblasting at only $100 (picked up/dropped off!!). Bug was sent straight to the crusher :(

Fri Jan 04, 2013 9:24 pm

I blasted my Ghia vert using the equipment at this company, CONSOLIDATED STRIPPING & DERUSTING, INC. http://www.consolidatedstripping.com I followed their rules listed here: http://www.consolidatedstripping.com/mediablastingrules.html and had no probems. No warping or distortion whats so ever. Sprayed it with DP 90 the following day and all is good.

Sat Jan 05, 2013 11:40 am

martyrg wrote: I blasted my Ghia vert using the equipment at this company, CONSOLIDATED STRIPPING & DERUSTING, INC. http://www.consolidatedstripping.com I followed their rules listed here: http://www.consolidatedstripping.com/mediablastingrules.html and had no probems. No warping or distortion whats so ever. Sprayed it with DP 90 the following day and all is good.
Wow. That is by far the BEST set of heuristics I have seen for blasting body panels. Thanks for the link.

I REALLY broke a LOT of their rules :(

After my limited experience and reading Consolidated Stripping's excellent rules for sandblasting body panels, I have some observations:

1) they reinforce the experience I had blasting on the INSIDE of body panels being critical
2) I was using WAY too high of pressure (~90 PSI) compared to their recommended max of 35
3) they recommend an "angular" abrasive and specifically caution against the glass beads I am using
4) they do not mention using a low angle, which many sites to recommend
5) They mention "peening" which I believe, but also persist in the thought that "heat" is an issue. I guess I should take a video with the FLIR to put this issue to rest.

Thu Jan 10, 2013 11:00 pm

I decided to test the adhesion of KBS RustSeal on:

* Bare metal, cleaned with a power wire brush
* Bare bead blasted metal
* Bead blasted metal, with zinc chromate.

We did each of these on both un-etched samples, and on samples prepared with KBS RustBlast.

Here is what the samples looked like when the paint was wet:

Here is what it looks like after a cross-hatch adhesion test:

My conclusions:

* Using a wire brush only, with or without etch does not get a good bond.
* Bead blasting without an etch does not get a good bond.
* We only saw good bonds on the bead blasted, etched samples.

The zinc plated, non etched sample had poor adhesion, but not worse than the wire brushed non-etched sample.

Etching the zinc sample is useless. The etch takes the etch off:

I might make one more test on the zinc plated sample, after scuffing it.

Wed Jan 23, 2013 10:54 pm

I still wanted to find a primer that would go over the Zinc Chromate, so I went to our local auto paint store with a sample and picked up their recommend two component (2K) epoxy primer, DP90LF, along with the activator and reducer:

I used the reducer to wipe a section of a Zinc Chromate plated fender, painted it, let it cure, and did the adhesion test:

I also did a test with no reducer wipe:

It looks like the adhesion was good in both cases, even over the Zinc Chromate.

The finish looks perfect, just the slightest matte:

Frankly I was scared of spraying, but I picked up a Harbor Freight HVLP detail gun, and the folks at the paint store walked me through the mixing, and I am very glad I took the plunge.

At this point I think I have a fantastic rust prevention system: The zinc chromate plated on the bare blasted metal, painted with the DP90LF 2K primer, then it will be topcoated with an 2K industrial coating.