Rust converter in a car - how do they work, where do they have limits?


If you grind rust spots in the car, it is strongly recommended to treat them with rust converter afterwards. You can read about how rust converters work, which chemical process takes place and what restrictions they have on their effects. Plus what you can use as a rust converter if you do not want to use the retail products.

Contained active substances in rust converters

In most rust converters, phosphoric acid is used as an effective substance. Only a few rust converters work on the basis of tannins, which are generally considered to be less effective.

However, there are also restrictions on phosphorus-based rust transducers, which are most frequently used in the automotive sector. This should always be considered in the application.

Mechanism of action of phosphoric acid

When rust comes into contact with phosphoric acid, a chemical reaction is initiated. The iron-III-oxide compounds that make up the rust are converted into more stable iron-III-phosphate.

The leafy rust (iron oxide) is converted into the more stable iron phosphate. The porous rust layer is thereby inactive. The rust can not continue because the reaction that led to the rust has been interrupted.

By solidifying the rust layer, the surface is also paintable again. It can be primed and used as a solid surface for a new paint coating.

Individual excipients accelerate the reaction and promote their implementation. However, the basic ingredient in rust converters is and will always be the phosphoric acid for each product.

Limitations of effectiveness

The process of rust conversion runs chemically as a stoichiometric process. This means that the reaction proceeds so that in the end rust and acid react in a certain ratio.

At the end of the reaction, rust may remain, which then worsens, or acid remains. This too is not a good prerequisite for the paintability. Of perfect conditions for a subsequent surface treatment so you can usually go out. The progression of the rust process can also be possible despite the use of the rust converter.

This is particularly problematic for vehicles where rust damage must be avoided at all costs - such as in a vintage car, because not enough replacements or spare parts are available. Rust converters must be used with care here.

Tips & Tricks

Rust converters can make sense on the exhaust or on the underbody - but the danger of rusting through is not always banned. This is especially true if the rust is caused by insufficient sealing and moisture from the inside.


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