Typical methods for removing rust
There are four main methods for dealing with rusty metal including: mechanical removal (grinding, sand-blasting, etc.),specialty paints, acids, and chemical converters. With the exception of chemical conversion, most procedures for removing rust involve dangerous toxic chemicals or require special equipment.
One of the most common methods of removing rust is by the use of grinders, wire brushes, sandpaper and sand blasting. These mechanical methods physically remove the rust from the metal surface. For minor rust, sandpaper will effectively remove rust. Heavy rust requires the use of power equipment that tears the rust away from the surface, exposing bare metal. Sandblasting forces large amounts of sand against the metal surface, breaking down the rust and some metal into fine particles that separate from the surface. Sand blasting is an effective process, but takes experience and specialized equipment. Additionally, if the metal is not primed immediately after sandblasting, rust will readily form on the porous metal surface.
Using mechanical methods requires care because being too aggressive my damage the metal surface.
While effective, mechanical removal is time-consuming and often requires specialized tools. Seams or recesses can prove to be particularly difficult when it comes to removing rust.
Special Rust Paints
There are a few paints on the market that advertise the ability to seal or encapsulate rust. They have chemical structures that have very tight molecules that will not allow moisture or oxygen to reach the rusted metal surface. The effectiveness of these products varies, depending on application and surface preparation. Because of the strong chemical nature of these products (toxic), gloves should be worn and adequate ventilation is important.Spraying requires special thinning solvents and specialized breathing equipment. In addition to being highly toxic, most rust paints are EXTREMELY FLAMMABLE and should be handled with caution.
Use of acids to dissolve rust is another method for rust control. A number of products on the market that deal with rust contain phosphoric acid. Acids dissolve the rust and leave behind a thin oxide coating on the surface. Because this coating is thin, it needs to be protected by topcoating with a quality exterior paint. When using acids, it is important rinse off the metal before the acid begins attacking the solid metal that remains after the rust is dissolved. Gloves should be worn and adequate ventilation is required when using acids. Because of the strong fumes associated with acids, spraying requires special breathing equipment.
Another process similar to the acid removal process is commercial stripping. In this process, metal (even an entire car frame) is dipped in a large tank of caustic soda at an elevated temperature. After the paint is dissolved, the metal is removed and rinsed with water and then put in another tank of alkaline solution and the rust removed electrolytically. This is an effective process, but requires a topcoating within a few days or rust will start. Because of the cost of this type of operation, these facilities are usually only available in large metropolitan areas.
A very old method of protecting metal from rusting is through chemical conversion. Blacksmiths were probably the first to discover this procedure when they coated their tools with oil and then heated them in a forge. This process created a very hard coating on the tool’s surface, protecting it from rust. Known later as “magnetite,” this very hard form of iron oxide is one of the most effective means of eliminating rust. And because magnetite is chemically inert, it does not react with oxygen or moisture.
Rust Doctor is a paint the uses the chemical conversion process. Two factors make Rust Doctor unique as a rust control system. The paint is a water based latex product, allowing brushes and spray equipment to be cleaned up with soap and water. In addition, because there are no strong acids or solvents in Rust Doctor, it is non-flammable and can be used in an enclosed environment without fear of dangerous fumes. This is especially useful when spraying Rust Doctor in a shop or garage. A second advantage of Rust Doctor is the fact it includes a primer that creates an excellent base for topcoating with any kind of paint. Once the conversion process is complete, the surface is left with a heavy coating of this latex primer. In one step, the rust is converted to magnetite and surface is primed. This primed surface will accept sanding primers, making it possible to create as smooth a surface as desired.