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Blasting and Dipping

By Jeff Zurschmeide

After you have purchased a car to restore and have carefully disassembled it, the next critical step to a successful restoration is to completely clean the body and chassis. Do not yield to the temptation to shortcut this process. Simply stripping and sanding off the paint you can see is not sufficient, because rust and shoddy prior repairs may lurk underneath the existing paint. The factory started with a bare metal shell, and so should you. The rewards of proper cleaning will far outweigh the cost in time and money spent.

Options for wholesale stripping and cleaning of chassis, hard parts, and bodywork come down to two basic procedures -chemical dipping and media blasting. But within each of these categories there are several options. Also, some of these options are inappropriate for different materials, so do your homework carefully.

At this phase of your restoration, your car should be disassembled to the very last nut, bolt, and screw. All trim and wiring should be removed in addition to glass, upholstery, gaskets and seals. If you read the page on disassembly, you will have catalogued all your parts and maintained a record of every piece.

Ask around in your club or at a car show for a reference to a reputable and high-quality stripping shop. You’ll spend several hundred to several thousand dollars on this process, and bad results can quite literally ruin your project. When you have some recommendations, visit each shop and obtain an estimate in writing. Also ask about the materials and process that each shop recommends for your car.

The very skilled or very adventurous amateur may choose to undertake the stripping process themselves, but most professionals leave this task to specialists.

If you choose to have your car blasted, here’s what you need to know:

  • Ask your blaster to use soda, plastic, or walnut shell media on outer surfaces. These substances remove paint and dirt, but do not warp sensitive sheet metal skins
  • Glass bead blasting will remove both paint and surface rust, but not deep rust
  • Chassis, undercarriage, cast steel, and other hard parts may be sand-blasted to remove undercoating, rust, sealants, and body fillers
  • Never use sand or heavy blasting of any kind on surface panels, roofs, hoods, trunk lids

If you’re interested in chemical dipping, remember these rules:

  • Disassemble your car completely before dipping
  • Use a magnet to ensure that all the pieces you intend to dip are made of iron-based alloys. Aluminum will be destroyed by standard chemical stripping, and requires a different stripping agent
  • Aluminum cleaning agents attacks steel, so separate all steel and aluminum-based components
  • Make sure that the chemical stripping process includes steam cleaning and neutralization of all chemicals used in the process. Otherwise the stripping agent may leach out of the bodys seams and destroy new paint

HINT Hint...

You may want to consider investing in a Rotisserie if you are contemplating a frame-off restoration. A Rotisserie is a large, heavy-duty stand that holds your car’s body or entire chassis off the floor, and allows you to rotate the chassis for convenient access to the undercarriage or any part of the car. This is especially useful if you’re facing large or complex rust repair or bodywork.

Dos and Don'ts
Thumb up  DO
  • Ask your club or experienced restorers in your area about the best businesses for stripping or blasting a car
  • Completely disassemble your vehicle before stripping
  • Get your estimates in writing before signing a work order
  • Make sure to separate and label aluminum parts, especially the VIN plate on your car
  • Use chemical stripping on doors, hoods, fenders, trunk lids, and other lightweight pieces
  • Use plastic, soda, or walnut media on visible surfaces of unibody cars
  • Use sand on frames and other heavy-duty components
  • Paint, prime, or otherwise seal stripped metal as soon as possible

Thumb down  DON’T
  • Don’t use sand blasting on lightweight sheet metal surfaces like doors, roofs, or hoods
  • Don’t allow any aluminum or pot-metal parts to be chemically dipped in caustic solutions
  • Don’t use a business that has little or no experience with automotive restoration
The Popular Restorations Feature Car
Author photo

1946 Packard: Removing the paint



When I purchased the Popular Restorations feature car, the paint was mostly original, although you could see there was some touch-up here and there. In the past I had a number of cars repainted, some in worse shape than the Packard, and never considered stripping them to bare metal. In fact, I didn’t even remove the trim.

But when I was visiting Custom Automotive Restoration, the owner showed me how rust can lurk under seemingly good paint. My goal was to restore the Packard so that, if stored properly, it would never rust again. So I decide to strip it to bare metal.

Now the question was to dip or to blast. You’ve probably heard the horror stories about dipping body parts. The theory is that the chemicals hide in the seams until after the car is painted, then it seeps out, ruining your new paint job. Apparently this has happened, but if the dippers knows what they are doing and rinse the parts properly, the chemicals will completely dissipate.

I took the doors, hood, trunk lid, front fenders, and a few other sheet metal parts to the dipper before dropping them off at the paint shop.

I had the body off of the frame and mounted on a Harbor Freight utility trailer. I had been warned that the body might flex or sag while off the frame, which could result in an improper fit for the doors. With that prospect in mind, I didn’t want to take the body off of the trailer and leave it at the dipping facility.

So I chose to have it walnut shell blasted as sand blasting can be too aggressive for body sheet metal, heating it up to the point that it warps.

One thing to be aware of is that the dippers and blasters do not want any of the original tarry sound deadening material left on the sheet metal. In both cases I had to pay extra to have it removed from inside the doors and inside the roof.

Once all of the paint was removed, nearly a dozen small, rusted-out areas were exposed. These were easily repaired and it’s feels good knowing the new paint will last for many decades.



Action Metal Stripping

By Jeff Zurschmeide

Preslee Jeffers owns Action Metal Stripping in Hubbard, Ore., and he took some time to chat with us about stripping cars for restoration:

PR: Can you give us a rundown on the stripping process?

PJ: First of all, you have to tear the car down -take the doors off, take the hood off, because you’ll get a better clean that way. Take out all the upholstery, glass, chrome and wiring. Take all the aluminum off, because the caustic used for dipping will dissolve aluminum. You have to tear a car all the way down to the shell,

PR: So absolutely everything has to come off?

PJ: Yes. Be sure to take the VIN tag off, because those are usually aluminum and you don’t want to lose that. You may want to engrave the VIN on the body, if you’re concerned about it.

PR: What happens once someone brings you the shell?

PJ: Then it depends on what you want. Some people like chemical stripping and some people don’t. The downside of chemical stripping is that the chemical can get trapped in the pinch welds and leak out 6 months to a year later. The chemical dries up, but when moisture gets to it, it reactivates. A lot of people will bend the pinch welds back so they can clean them out, or they’ll remove the skins from the structures entirely and reinstall them afterwards.

PR: What’s involved in chemical stripping?

PJ: The dip solution is a caustic soda. It’s an alkaline called sodium hydroxide. We heat it and it removes paint, grease, oil, and undercoatings, but it won’t remove rust. So you have to put the car in a bath of muriatic acid to remove the rust, then you pull it out of the acid, steam clean it, and put it back in the caustic to neutralize the acid.

PR: But chemical dipping doesn’t work on aluminum, right?

PJ: If you put aluminum in caustic dip, it’s guaranteed not to be there when you’re done. Aluminum is a very soft material. We have a chemical strictly for aluminum, called methylene chloride. It’s not a caustic and it’s not an acid. It’s a solvent-based product that removes paint, powder coat, grease, whatever. Some cars are particular problems. For example, on Austin-Healeys the skins are aluminum, but the frames are steel, so it’s a challenge because the methylene chloride will make steel rust.

PR: Tell me about media blasting.

PJ: With media blasting, we use plastic, glass, walnut shell, or sand. Plastic works great for removing the paint, but won’t remove rust at all. Glass will remove the paint and surface rust. Sand will remove everything, but it’s very aggressive and will have a chance of warping panels. Sand’s the worst.

PR: But there are parts of cars that shouldn’t be blasted, right?

PJ: The metal skins on doors and hoods are thin, and there’s not much bracing behind them. They’ll warp if you blast them. We don’t use sand on surface body panels, roofs, hoods, or trunk lids. We dip the doors, hood, fenders, then go over it with a really light blast afterwards. For a chassis, we’ll sandblast it. We’ll also use sand for brakes, suspension pieces, and other parts that are made of cast steel.

PR: Which process is better?

PJ: People like chemical stripping because it leaves a nice a finish, and there’s very little metal loss. But they don’t like chemical being trapped in pinch welds and inside of box sections like rocker panels. But with any type of abrasive blasting, there’s a dust issue. There’s always a little bit of material left in gaps, spaces, and box sections. It’s up to the customer which one they prefer.

PR: What should someone do with a car once you’ve stripped it?

PJ: You need to seal the metal immediately after stripping. It’s not so bad in the summertime when it’s dry, but if it’s wet, you need to get it to the body and paint shop ideally the same day. We get on the phone with the customer as we’re finishing up, so they can get the car right in to be primed, sealed, or painted in some manner.

PR: How much is this likely to cost?

PJ: That depends on the size of the job, really. People should always compare prices between vendors. When we’re blasting, we charge by the hour and we know how long it takes to blast a particular size of car. Chemical stripping is always the most expensive. To get a body chemical-dipped, you’ll pay 2 to 3 times as much as to blast it.

PR: How should someone evaluate a blasting or stripping shop?

PJ: In our business, it goes by reputation. Car guys can join a club if they don’t know people who have done restorations. If someone is talking from experience, they’ll be able to tell you where to go. If you don’t have that, ask a business for references.

PR: Anything else to add?

PJ: Always get your estimate in writing, because sometimes you go to pick up the car and it won’t be the same price as when you dropped it off. You don’t want to be surprised at the end.

Click on any item below for more details at Amazon.com

John Pfanstiehl
Automotive Paint Handbook: Paint Technology for Auto Enthusiasts and Body Shop Professionals
HP Books, Paperback, 1998-08-01

This is an excellent resource, with plenty of detail provided by paint manufacturers and professional tips based on experience. Basic prep and painting is covered in detail, and extra information is offered on custom paint styles and techniques.

Dennis W. Parks
How to Paint Your Car
Motorbooks, Paperback, 2003-10-12
This book is an excellent choice for the restorer who plans to paint his or her own car. The text covers modern paint chemistry, offers air pressure drop tables, and covers often-overlooked areas such as masking and paint gun settings. The bodywork section is light compared to some other books, but offers great details in surface preparation and paint application technique.

Pat Ganahl
How to Paint Your Car on a Budget
S-A Design, Paperback, 2006-06-30
This is a great basic paint book. If you just want to throw a nice coat of paint on a car, this book will tell you how to do it. If you are going for the complete 100-point absolutely perfect show car paint job, this is not your book. Basics of bodywork are covered, as is paint prep and the sanding/cutting/blocking process. Paint jobs at several different levels of commitment are detailed in step-by-step procedures.
External Links

Wikipedia has a good overview article on abrasive blasting.

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