I just notice a few bubbles in the paint and decided to investigate. With a steel brush I removed enough paint to see the exterior damage.

Picture of the right rear quarter panel at the rear wheel well.

Inside I found a more insidious situation.

Which blasting media should I use to expose all the damage? Tips and tricks are appreciated.

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I’ve used the miracle paint/fiberglass method which still holds up 2 years later.

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Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz

Ugh, that looks nasty! Good thing you caught it when you did.

Media blasting is a mixed bag.

Sand is the fastest, most efficient but it has its problems. It strips EVERYTHING from the area you are working. Paint, rust, thin sheet metal, weather stripping, sealant, rust preventative coating, you name it. An over exuberant application can also weaken the surrounding metal. It is a pain in the arse to clean all the media from the areas where it WILL infiltrate. The use of a good respirator system/device, goggles, gloves and head covering is a must! You definitely do not want to do this in an enclosed area such as a home work shop. You'll be cleaning the detritus from this for months and that includes orifices/wrinkles on your body you didn't realize you had.

Glass beading is the next most efficient method. Not as aggressive and not as harmful to existing metals/painted areas, etc. as the sand. Tends to leave a "mottled" surface. Same precautions need to be taken regarding protection. Clean up is a LITTLE easier, but not much.

Walnut shells are next. I'm not impressed with their rust removal properties but they do work. Much slower and not as efficient as the previous methods but it does have the advantage of the media being organic and if you happen to leave a mess in the yard, with the exception of the removed rust, paint, etc. , it will all wash away the next time it rains. Same safety precautions. Clean up is easier. Shop vac, compressed air nozzle and a little brush work will get 99% of the media from the work area. Easier to shower off also.

Soda blasting is last on my list. Most expensive and least effective cleaning heavily rusted areas. Does a great job removing paint without damaging the surrounding materials but that in itself speaks for its rust removal ability. It'll knock off the loose, flaky stuff but it doesn't do a good job on the deeper corrosion. Easiest to clean. Just hose it down and all the media dissolves. Give it a good blast of compressed air to get the water out of hidden areas and you're done.

Me? I wire brush to determine the extent of the corrosion and bead blast the rust. What I find after the beading determines my next step.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Lord willing, I'm just trying to remove enough off of the metal to see where to make the cuts that will eliminate all that rust. I intend to cut the sheet metal off my donor car and fit it properly without painting the entire body.

Will soda remove the coating on the interior?

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In that case, I wouldn't mess with media blasting. Use a chemical stripper to determine the extent of the rot.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Chemical strippers 'ain't what the use to be,' but that might be the way to go. I have a few quarts I bought to strip the varnish off the interior wood trim left. None of it worked. Jasco, some Kleanstrip products and maybe one more.

I'll try it and let you know.

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I've had good luck with the Jasco line, even on the trim varnish.

The trick to the trim is coat it with a slime coat, bag it for a day, wipe it down, re-coat, bag, wait, scrape with a plastic or wood scraper, lather, rinse and repeat until the varnish is gone. Usually takes me four or more applications to get get rid of the stuff.

You'd think that something so hard to remove would last forever, wouldn't you?

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

I doubt Mercedes considered these cars would be as popular and last as long as they have.

California declared war on Methylene Chloride which Kleanstrip used in their top stripper so KS discontinued the line by removing the chemical. Strippers ain't what they once were. Other strippers may have included that chemical.

Even when KS put Methylene Chloride in their strippers it took a couple applications to strip the MB varnish. MB sure didn't want their finish to come off.

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Any progress?

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

No, before I start this I need to buy a few tools, a welder, a nipper to cut the metal straight, a punch and offset tool. I also need to line up some 2 part epoxy to seal everything up with.

It may be another month before I actually do anything but practice cutting sheet metal and welding the pieces back together. I've never worked with sheet metal, only heavy steel.

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Here's a handy little tool for sheet metal work.

https://www.amazon.com/Astro-Pneumatic-Tool-930-Blades/dp/B006RF96AM?ref_=fsclp_pl_dp_3

Ingersoll-Rand has a nice one also. I believe it is the 429G model.

Sure is a lot nicer than using a cut-off wheel. Buy a swivel air fitting or hose for ease of use.

https://www.amazon.com/Milton-S-680-2-30-Inch-Snubber-Hose/dp/B0000AXCAV/ref=sr_1_31?keywords=flex+air+hose&qid=1572094617&sr=8-31

https://www.amazon.com/Swivel-Air-Hose-Fitting-Male/dp/B002HF0QTG

I rivet a piece of flat stock at the point I want to cut to get a straight edge.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Does a saw prevent metal expanding from heat? Being that I'm going to cut less than 5 feet total length I wondered if the 20 dollar tool from harbor frieght might work well enough.

What is the best 2 part epoxy primer? Are transtar, Dupont or Utech good products or do you have better results with another?

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Spray or rattle-can? Before or after welding? Welded patch or epoxied? Lot's of variables need to be considered.

The saw will generate heat if you try the "git 'er done" method but not if you use it properly.

It's your money so buy the HF model if you want.

I warn you, once you use a good air saw then you'll find yourself using it more often. You will regret buying the HF model.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

I don't think my compressor will handle air saw and I don't expect to ever need this saw again.

I'm gonna need more than a pint of epoxy primer. I was wondering what the best is.

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I get good results from the "Transtar" line of 2K products. A couple of buddies swear by the SPI line but I have never used it.

I usually buy my products from FINISHMASTER. Yeah, I pay a little more but I feel the support from them is worth it.

Whatever brand of 2k primer/sealer you decide upon, be sitting down when you ask the price!

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now