What is the Difference Between Rust Dissolver and Fast Etch?

A question that often comes up when trying to remove rust is which product works best and why. While Eastwood offers solutions to either encapsulate or covert rust in place, two products are designed to remove it entirely. Both are acid-based products but differ in their purposes.

Rust Dissolver, as the name suggests, dissolves rust without damaging the base metal. Fast Etch is a metal etching solution that also removes light rust from ferrous metal but also leaves behind a phosphate finish.

So how exactly are these two products different, and which one is best for your needs? That depends a lot on the project you’re working on and what you plan to do once the rust is gone. To demonstrate the similarities and differences, we grabbed some rusty chassis hardware and compared them side by side.

Rust Dissolver

How it Works

Eastwood Rust Dissolver is a hydrochloric acid solution that reacts with ferrous oxide (rust) on steel and iron materials. It should be applied to clean, non-greasy parts and requires anywhere from a few minutes to several hours to react. In the case of our experiment with rusty nuts, bolts, and washers, we immersed the hardware completely for about 30 minutes.

After soaking in the solution, parts must be neutralized to prevent the acid from continuing to react. We laid the parts out on absorbent mat material and used Pre-Paint Prep Solvent as a neutralizer. We sprayed all sides with the cleaner and then patted them dry to remove any residue. A base product like baking soda would have also worked.

Results

As expected, the rust had dissolved from surface of the metal, leaving behind clean, bare steel. At this point, the hardware could be re-plated, painted, powder coated, or treated with a rust-inhibiting solution. However, assembling the bare nuts and bolts without some kind of treatment would not be advised. In just a matter of hours, the bare metal would eventually develop another light coat of rust in most conditions.

To test and confirm this we allowed the clean, dry, neutralized part to rest untreated overnight in our climate-controlled workshop. In just that short time, the parts had developed a new skin of rust on the surface.

Best Use for Rust Dissolver  

Rust Dissolver is best suited for removing heavy rust without damaging the metal beneath it. Ideally, you want to soak or submerge rusty components until the rust is cully removed. Objects like hardware, brake calipers, brackets, and other small parts can be soaked in small containers. Larger items, like axle housings, engine blocks, and other assemblies can take advantage of Rust Dissolver Gel. This has a thickening agent to hold it in place on vertical surfaces.

It is critical that the parts being treated remain fully soaked until you’re ready to neutralize the reaction. That may require regular spraying to keep surfaces wet, or possibly wrapping the treated part in plastic film to maintain its liquidity.

Once treated and neutralized, it’s critical to further treat the metal with primer, paint, powder coating, plating, or some other permanent anti-corrosion method. Failure to do so will result in rust returning in short order.

Because it’s a fairly strong acid, Rust Dissolver should not be used on chrome plating, as it may remove the finish. It is also not advisable to use it on aluminum or other soft metals, which don’t technically rust anyway.

Fast Etch

How it Works

Eastwood Fast Etch uses a different acid component to dissolve light rust on surfaces. Instead of hydrochloric acid, it uses phosphoric acid, which has the benefit of leaving behind a corrosion-resistant phosphate coating.

Applying Fast Etch is similar to using Rust Dissolver. Typically it’s sprayed or wiped on steel or iron surfaces with lighter rust, often after blasting or other metalwork. It also must remain wet while working and then immediately neutralized afterwards. Both these step ensure a clean, neutralized surface that can be finished successfully.

Results

We soaked part of the same batch of hardware used in the Rust Dissolver test in a tub of Fast Etch. As the parts came out of the solution and were cleaned and neutralized with the same Pre-Paint Prep, they looked very similar. However, once the dried completely they developed the signature dull gray phosphate finish on the surface.

We stored these parts on the same test sheet as the Rust Dissolver-treated parts for the overnight test. Unlike the other parts, those treated with Fast Etch developed no new rust overnight. The phosphate coating prevented that from happening in the short term, though it’s not intended as a permanent rust preventative.

Best Use for Fast Etch

Fast Etch is truly a metal conditioning solution more than strictly a rust tretemnt. As such, it’s made to remove light rust from surfaces before other finishing. It etches the surface for better adhesion of primers, fillers, paints, and powder coatings. The phosphate coating can provide temporary protection while your project receives other work.

Fast Etch should also be avoided on chrome parts as it may mark or remove the plating. However, it can be used on aluminum and other sift metals like brass to help enhance adhesion.

Conclusion

Depending on how much rust your project has and your plans after removing it, there are a couple different options. Rust Dissolver works best for heavy rust that will immediately be treated or finished. Fast Etch works well for lighter rust but leaves behind an anti-corrosion coating that buys you extra time for additional prep.