There are various services involving acids, when applied to the maintenance of an aluminum trailer. An acid washing is usually the application of a mild acid, that removes the oxidation of the aluminum, that allows the exterior surface of a trailer to become dull and less attractive.

 Aluminum has a process, whereby the exterior surface forms a naturally occurring, microscopically thin coating of oxidation, that protects the base metal from the elements. This is also found in stainless steels and various ferrous steel alloys used in the construction trades.

Unfortunately this is undesirable to those who want their trailers to not look dull and want the bright, polished appearance. This oxidation is removed by the application of a very mild acid wash or "brightener". Unfortunately it results in the removal of the oxidation and the aluminum's natural protection to the elements, so the process again restarts. Waxes and various finishes can retard this condition somewhat, but not totally eliminate the process.

Pitting and active corrosion can only be stopped by the application of a mild acid, which stops a chemical reaction, wherein foreign materials are attacking the cellular structure of the base metal. This occurs because the aluminum's oxidation was breached, usually by the lack of oxygen and a mechanical abrasion to the surface. This combination is routinely found under urine soaked rubber mats.

Washing the affected area with water will slow the process, but not stop it. The application of a mild acid like Muriatic will stop this corrosion, clean the surrounding areas, and allow the aluminum to again start the oxidation process. If this is not performed, the corrosion will continue, and major structural damage can occur to the aluminum.

Acid etching is usually done to better prepare the metal for the application of a surface coating. Most acids will etch the metal, the more aggressive the acid, the more effect it will have. Many specialty primers that are used for aluminum will have etching qualities, and allow a better adhesion. This separate process is not necessary if the surface will not be coated.

Gard

You're correct. After flooding the acid with water, when you're done with it's application, let the floor completely dry before installing the mats.