Rust Converter versus Removing Rust and Sealing Metal – Which Protects Metal Longest?

Most everyone knows that once metal starts to rust it will continue to rust until the metal is completely eaten away. So, it’s important to stop rust as soon as it’s discovered. Here we will discuss two methods used to stop rust. The first is using rust converter to convert the rust to an inert primed layer that can stand alone or be painted over. The second is to completely remove the rust from the metal, and then apply a rust preventive paint or coating to protect the metal. Both techniques will stop rust and seal the metal from moisture and oxygen to keep it from rusting in the future. However, results will vary when it comes to how long the metal can be kept free from future rust and what the quality and appearance of the finish will be.

Method – Using Rust Converter

Rust converter, also known as rust reformer, is a chemical solution or primer that can be directly applied to the metal surface to convert iron oxide (rust) to a protective chemical barrier that is resistant to moisture and protects the surface from further corrosion. Rust converter is comprised of phosphoric acid or tannic acid or a blend of both. Phosphoric acid rust converter turns the iron oxide into a ferric phosphate inert layer. It can be used on metal parts that are exposed to exterior weather conditions if it is top coated with a quality paint or coating. Tannic acid produces a protective bluish-black ferric tannate inert primer layer, which can stand alone to protect against exterior weather conditions or be painted over for better appearance. The layer acts as an excellent primer for both oil and epoxy-based paints. Rust converter can be used on any rusty iron or steel object; however, it will not work on aluminum, copper, stainless steel, or galvanized metal.

Benefits of Using Rust Converter

With the rust stop techniques being discussed here it is necessary to first remove any loose or flaking rust with a stiff bristle brush, wire wheel, or sandpaper before using rust converter. This is done to provide a stable surface. It’s important to not remove all rust since it would defeat the purpose of rust converter which chemically bonds to rust and seals it in. Application of rust converter is a simple and quick procedure compared to eliminating rust and sealing the metal with a rust preventive coating. This is especially advantageous when time to complete the project is limited or the object is large and thorough rust removal would be highly labor-intensive.

Drawbacks of Using Rust Converter

When done properly, eliminating rust, and sealing the metal with a rust preventive paint or coating can provide a longer lasting solution than rust converter. While time and labor are reduced on the front end with rust converter, the procedure will have to be repeated before too long. In some cases, a good rust elimination and metal seal job can provide protection from future rust four to five times longer than using rust converter.

Another consideration is that finish quality can be compromised when using rust converter. Eliminating rust typically provides a smoother surface for rust preventative paints and coatings, which allows for a smoother and better appearing final finish. Also, rust converter is designed to bond to rust. So, it won’t work on non-rusty surfaces or surfaces where there are a mix of rusty and non-rusty areas.

KBS Rust Converter

KBS coatings offers Rust Converter that easily converts a rusty surface in to a black, inert primed surface that is ready for paint and is compatible with most topcoats. It is offered in aerosol form for easy application and is fast drying. More information is available here.

Method - Remove rust and seal the metal with a paint or coating

For stopping rust, the best and longest lasting result is achieved by eliminating rust and then using a primer to seal the metal from moisture and oxygen and then applying a top coating with paint or other coating. It’s important that the rust is thoroughly removed and a strong bonding and durable paint or coating is applied.

Rust Removal

Rust can be removed with chemicals, solvents, and abrasives. As when using a rust converter, the initial step is to remove loose flaking rust with a stiff bristled brush or sandpaper. The following are examples of rust removal methods.

Chemicals and Solvents

White Vinegar - White vinegar will dissolve rust when the metal is soaked in the for a few hours. This leaves a “rusty paste” which can be scrubbed off with a stiff brush. For objects too large to directly soak in white vinegar a layer of vinegar can be poured on and after allowing time to set the metal can be scrubbed off.

Oxalic Acid – Oxalic acid is a compound that is odorless and appears as a white crystalline solid. When mixed with water it produces a colorless and odorless solution. As it is an acid, care must be taken during handling, including gloves, a mask, and safety goggles. The metal object is then soaked in the solution. Results can be seen within 20 minutes, though in cases of heavy rust, it can be soaked for up to 24 hours.

Petroleum-Based Solvents - Products like WD-40 can be used to remove rust and are not as corrosive or toxic as acids. Expect to wait up to 24 hours for petroleum-based solvents to take full effect.

Water Based Rust Removers - Acid-free, water-based rust removers lift the rust from the metal through a process called chelation. Chelation causes molecules within the rust removal solution to bond with rust and draw it away from the underlying metal and into a substrate. The rusty object is typically immersed in the solution, or the rust remover is sprayed on. The rusted object is then left for 30 minutes to remove light rust, or up to overnight for extremely heavy rust.

Abrasives

Using abrasives is a mechanical form of rust removal which easily removes rust. Examples are sanding by hand or use of power tools like an angle grinder, sander, or a drill fitted with a surface finishing disc, cup brushes, or wire wheels. Sandblasting is also a popular and easy way to remove rust and it provides the metal with a surface texture that allows paint to firmly bond.

Painting/Coating

After rust has been removed the metal needs to be sealed to prevent it from rusting in the future. A primer is applied and then is usually top coated with a paint or coating. Of note, some paints include a primer in their formulation.

Primer

While metal paint primer is not always a requirement, it is always recommended, especially if the metal will be in contact with moisture. Depending on the type of paint or coating used as a top coat, the metal may or may not require primer to seal it before the top coat is applied. There are a variety of primers available and most popular are self-etching primer and epoxy primer.

Self-Etching Primer - provides a strong bond to the surface and prepares and seals metal from air and moisture. Self-etching primer uses an acid to micro-etch the metal for a slightly rough “anchor pattern” surface profile (like that achieved by sandblasting) that provides increased grip for the primer which in turn provides a strong base for the top coat for best overall adhesion. Some self-etching primers deposit a layer of zinc phosphate for increased adhesion. Self-etching primer cures quickly, which helps reduce project times.

Epoxy primer provides excellent adhesion when priming metal but because it doesn’t etch the metal like self-etching primer. The proper surface profile must be created manually by sanding the surface with 80 to 180-grit sandpaper, or by sandblasting. Of note, epoxy primers take longer to cure than self-etching primer.

Paint or Coating

When top coating the primer it is important that the top coat is compatible with the primer. No type of paint will bond to unprepared epoxy paint. Because epoxy painted surfaces don’t allow adhesion, they must be abraded before they will accept new paint. Sanding the old epoxy finish with a 120 to 220 grit sandpaper will promote adhesion. Once the epoxy has been abraded, any type of paint will bond to it.

Benefits of removing rust and seal the metal with a paint or coating

As long as the job is done effectively, the best and longest lasting result for stopping rust is achieved by eliminating the rust and then sealing the metal from moisture and oxygen. Also, the finish quality is better than using rust converter.

Drawbacks of removing rust and seal the metal with a paint or coating

One drawback of removing rust and sealing the metal with a paint or coating are that it the procedure is labor intensive compared to using a rust converter. Also, the cost of materials will usually be higher. However, in this case you certainly get what you pay for.

KBS Coatings 3-Step System

KBS Coatings offers the user-friendly 3-Step System to stop rust. It performs all the functions necessary to properly remove rust and seal the metal for the best long-term protection against rust.

After removing any loose or flaking with a stiff bristled brush, or sandpaper KBS Klean, a biodegradable cleaner that removes dirt, oil, grease, and other contaminants is applied and scrubbed with a scrub brush or scouring pad.

Next RustBlast, a water based and biodegradable solution is applied to dissolve and neutralize rust. As well, it acts as a pre-paint primer, and provides the metal with an etched surface profile for solid paint adhesion. After spraying on it is left to sit (while keeping wet) for about 30 minutes and then is rinsed off with water.

Finally, RustSeal, a single part coating that seals metal away from moisture and oxygen is brushed, sprayed, or rolled on to form an attractive, tough, ceramic-like coating that is hard to chip or scratch, and won’t crack or peel.

More information on the KBS 3-Step System can found here.

So, what’s best for stopping rust?

Ultimately, it will come down to your goal for protection longevity and visual appeal. KBS Rust Converter will do a good job of stopping rust and is a relatively quick process compared to eliminating rust and sealing the metal with a paint or coating. However, it won’t protect metal as long and the finish quality won’t be as smooth and attractive.