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Home | BusTech | Service Directory | Spot the VW! Rust Prevention, Removal and Treatment On this page:
Introduction This article is culmination of experience and significant investigation using freely available online resources. Where possible, multiple references (or more) were used for each section to avoid biased, false, misleading information. DISCLAIMER: Please use caution when working with any kind of abrasive or corrosive product. Always wear eye protection. Keep skin covered. Wear a face mask. Keep water nearby. Keep the area you are working in well ventilated. You should always have someone nearby who has been notified of your activities - just in case something happens, they will be able to assist you, and they will know how to describe what you were doing to emergency personnel if needed. If you have any doubts about your abilities - please seek the advice of a trained professional. Information provided on this page is for your edification - and is not intended as a specific guide or recommendation. Use this information at your own risk. What is rust? Rust is a byproduct of the reaction (oxidation) that occurs when iron-ferrous metal (metal with iron in it) is exposed to oxygen. This article uses the term 'metal' to mean iron-ferrous metal, steel or steel alloy (steel with other metals mixed in). Sheet metal, is steel rolled into thin sheets. Obviously there are other types of metal that do not contain iron, such as alluminum. (See the links to Wikipedia and the American Iron and Steel Institute for more glossary terms.) Air contains water which accelerates the oxidation process because the hydrogen helps to bond oxygen to the metal. The more moisture in the air, the more quickly the metal will rust. Metal is slightly porous, enough so that moisture can be absorbed into the metal. As the rust occurs more quickly when exposed to moisture, the rust can "dig" into the metal. This is how metal "rusts through" to an unexposed side. Technically, there is no such thing as surface rust, as rust begins in the microscopic valleys of unprotected metal. These valleys are receptors of moisture. If you have ever de-rusted a part, it will look "pitty" as if the rust caused small holes or dents in the metal. When rust forms, it begins as a small dot and spreads outward in all directions. Several good articles on rust are: When unprotected metal is exposed to air the metal rusts. Metal can become unprotected when the outer layer is damaged. Keeping all areas of the car clean go a long way towards preventing rust. Road Salt isn't necessarily the essential ingredient in forming rust. Road salt is corrosive and causes protected surfaces to deteriorate, which eventually exposes the metal to air, and once exposed to air the metal will rust. (And usually where you find salt, you will find an environment that has more moisture content in the air.) Read: Sodium Chloride: A Rant and Rave, by Raymond Magliozz An interesting article describing the use of calcium chloride or magnesium chloride in the prevention of snow formation on roadways, and the impact corrosion has on braking components, is available from Brake Pro. An old car has usually had many owners. And with a few exceptions, used car owners are careless when it comes to maintenance of their auto. Dirt formation, usually from infrequent cleaning is common. Think of all the times you have stepped into your car with dirty shoes. That dirt travels down through the carpet and rests on the metal below. Dirt absorbs moisture, which over time will rust a hole in the floor. This situation is exacerbated as the car ages and weatherstripping begins to leak, or corrosive chemicals (brake fluid, gasoline, coffee) come in contact with the dirt. The deterioration accelerates, the car loses value, and each successive owner cares less about maintenance. You should keep this in mind when contemplating the purchase of a classic "daily driver." Before we look at the different ways of removing and treating rust, we need to agree:
There are many different ways of treating rusted metal and everybody has an opinion on the best method. Abrasion Abrasion or sanding is the most popular method of treating rusty areas because it is the most simple and for most people involves simply a sheet of sandpaper. Abrasion can also be in the form of a wire wheel brush or synthetic fiber wheel.
Note: Some people claim that any sanding on a rusty surface can damage the metal underneath the rust. Because I can find no evidence that this is an issue, I will leave it up to you to decide. I will say though that aggressive sanding can damage the metal underneath - but it is nothing that cannot be resolved by metal prep, acid etch primer and a good body filler. Media Blasting Media Blasting is most commonly known as sand blasting (or sandblasting). It is a method of using compressed air to spray metal with abrasive material. There are many different types of blasting media depending on how aggressive you need to be (how much rust you need to remove). The newest and most exciting media blasting technology is the use of baking soda. Soda blasting decomposes rapidly when it comes in contact with a surface. As a result, there is less byproduct from the blasting activity. Soda blasting equipment is available in larger metropolitan areas.
Media Blasting Q/A Q: "some people have told me to have the car media blasted and not sand blasted." Q: "media such as walnut shells is twice as expensive as sand" Q: "I'm told that sand blasting will warp the body panels" Note: The gauge of the metal also affects how prone the metal is to warping. I had a '65 Mustang sand blasted - no problems. However, the same person who sand blasted the Mustang refused to blast my '65 VW Bus, because he was worried about warping the metal. The Mustang uses thicker metal than the VW. Q: "The sand blasting company says they have 20 years experience and know to turn down the pressure and keep the nozzle at the right distance and it will be fine. He has included references. Q: "If this decision was only going to save me $100 I wouldn't have to think about it but sandblasting is $750 cheaper. Conclusion: There are several new technologies in media blasting that have made sand obsolete. The first is dry ice or CO2 blasting. ICESonic is a company that makes equipment. ICESonic USA has videos of the dry ice blasting process. With dry ice blasting, the media evaporates upon contact with the metal. This leaves no blasting media residue - only what was on the metal to clean up. The second is soda blasting or Sodium Bicarbonate Media Blasting. This process uses specially prepared baking soda as the media. An example of a company specializing in this type of equipment is Pacific Soda Blast. Generally, soda blasting equipment is much cheaper than dry ice blasting. There is media left behind, though, and the media will damage soils because of its very high PH level. These methods require specialized and expensive equipment. In large metropolitan areas, you can rent these types of units. However, in most areas, they are not available. Hydroblasting Hydroblasting, or water blasting, uses accelerated water particles as the blasting media. Only in the last several years have very high-pressure water blasting equipment been available at a relatively low cost. Water blasting offers some benefits over other types of media blasting. The first is the low cost of the media. The second is relatively easy cleanup of the media (given a discharge area is available). In some situations, however, you may not want water as your media. Water carries pollutants beyond the primary blasting area. (Your locality may have laws against the discharge of pollutants.) Second, water is corrosive to unprotected metal. Hopefully you can perform the blasting on a dry, sunny, warm day. Hydroblasting equipment can provide heat to the media to dissolve grease and other materials. The equipment may also allow additional chemicals to be added to the water prior to blasting to increase corrosion (such as acid or base) or to decrease post-blasting deterioration. Generally high-pressure blasting equipment is available for rent. You probably will not find professional services offering hydroblasting in your area. An excellent training video is available online from Ausject Inc. (Windows Media Player is required.) Corrosion Corrosion is another common method of removing rust, involving the use of an acid or base to corrode or "eat" away the rust. Phosphoric acid is the most common chemical used for this purpose, as the chemical reaction with the rusty areas (and metal) leaves a film of phosphates on the metal's surface. You can use almost any other kind of corrosive product - like pool cleaner, and even mollasses! Corrosion can be in the form of a liquid or gel - and in the case of chemical dipping, a vat large enough for a vehicle. I have personally used Phosphoric acid and a garden sprayer. PLEASE WEAR EYE AND SKIN PROTECTION! This application method allowed me to quickly cover an area that was difficult to reach. Apply it and let it do its work. Tell all children and animals (and other adults) to stay away until you have neutralized the acid (using Metal Ready or other metal wash). If you are considering using a corrosive method of removing rust, you should be aware of the term metal (or hydrogen) embrittlement. Heavy iron metals, which are usually used in suspension components, are susceptible to weakening after coming in contact with acid. However, generally you have to use a large amount of acid for this to occur - or soak your parts in a high-concentration of acid over a long period of time. The key here is to not treat suspension or steering parts with acid for a long period of time.
Conversion Conversion is a technique that "converts" a rusted area into an inert (iron-oxide) compound - which then covers the deeper rust preventing further oxidation. A rust converter can be in the form of a chemical - or can be an electrically induced reaction.
Chemical-based rust converter products are the most prolific of "cheap" rust products - often promising miracle results. Unfortunately, chemical-based rust converters often do not achieve long-lasting results. This is because the resulting compound that is created by the conversion process often acts as an actractant, a powdery layer that does a great job at trapping moisture. Encapsulation Encapsulation does not affect the rust, but rather encases the rust underneath an impermeable layer. Products that use the encapsulation process are often associated with terms such as "rust inhibitor" or "rust proofing". The most popular product to use this method is Por-15.
Products that are sold solely as inhibitors do very poorly over a long period of time. This is because they are fairly weak as a barrier against moisture. Products that offer rust proofing are better, but often use oil or wax to provide a more protective barrier. A popular oil-based rust proofing product is called Krown. Gas tank "repair" kits often use an encapsulator to trap in rust and loose particles. Keep in mind though that at some point, the encapsulation will weaken and you may find yourself pulling that tank again to re-treat the tank. Encapsulators are great for either extremes - the rust is so pervasive that treating the area would be too time-consuming or expensive. Or, the rust is so mild and you are in a low-rust area that it is not worth the effort to completely repair the rusted area. Otherwise, rust proofing products are best kept to new cars applications (where there is no rust activity) or on new metal panels to prevent future activity. One encapsulation product that shows promise is Rust Bullet from Caswell, a company that specializes in metal restoration and electroplating: Repair Products > Rust Bullet Rust Preventative Paint Rust Bullet is an encapsulation product that does not require other chemical preparation (unlike Por-15). Their site includes some good useful comparisons with other (similar) "rust-proofing" products such as Rust Oleum, Choosing a rust removal process The selection of which process you use to treat rust depends on how much money and time you can spend on the task. Also affecting your decision is your ability to reach the affected area. It is obviously best to use a process where it is most effective. For example: Location
Cost:
Longevity
I have personally worked with the following methodology:
If we were going to treat an undercarriage - we would apply Por15 or an encapsulator after removing the oxidation. When the Por15 is "tacky" apply an epoxy primer to the surface if you intend on painting over it. Once dry, Por15 will reject paint - so you have to apply paint when it is tacky. Keeping areas clean and inspecting areas that have seen previous rusting is important. Painted surfaces, door jambs, trunks - any area that is painted - should be kept clean. After cleaning, using a wax (even a spray on wax) will help protect the paint. You can safeguard against oxidation by using a non-corrosive oil-based aerosol over an area that is likely to be affected by rust. The oil will prevent moisture from coming in contact with the surface. If you have a painted surface, such as under a vehicle, a dry graphite coating also works well. I have learned my lesson, and keep suspension components lubricated with heavy grease. Grease acts as a vapor barrier and prevents oxidation. My favorite here is white lithium grease in a spray can - as it is easy to apply on a large area. As I was working on my brakes, I came to realize an important two-step process: clean and grease. On the black suspension components, a black molybdenum grease is heavy and inconspicuous. Remember, grease is relatively cheap. Rust removal is fairly expensive and time consuming. Additional Resources Acid Pickle (final stage prior to plating) Chrome Plating discussion (by John Bercovitz) Note: I am not a chemical engineer. If you have a suggestion for the content of this page, please mail me. |