4.4 Cleaning, Corrosion Control, and Finishing

Cleaning, Corrosion Control, and Finishing

Cleaning and corrosion control are not cosmetic subjects. The ACS includes aircraft cleaning procedures, corrosion theory, types and effects of corrosion, corrosion-prone areas, preventive maintenance, inspection, removal, treatment, corrosion preventive compounds, high-pressure application equipment, cleaner compatibility, dissimilar metals, conversion coatings, protective materials, primers, topcoats, surface preparation, ambient conditions, placards, finish inspection, personal protective equipment, fire prevention, and control-surface balance after refinishing.

Corrosion is the deterioration of material through chemical or electrochemical action. Moisture, oxygen, salt, industrial pollutants, battery electrolyte, exhaust residue, trapped dirt, and dissimilar-metal contact can accelerate it. A protective barrier can slow corrosion, but a scratch, failed sealant, missing primer, or contaminated lap joint can create a local corrosion cell.

Cleaning starts with material compatibility. Aluminum, magnesium, steel, composites, plastics, transparencies, rubber, and painted surfaces may require different products and methods. Strong alkaline or acidic cleaners can damage aluminum or finishes. Solvents can craze plastics or attack composite matrices. High-pressure equipment can drive fluid into bearings, seams, connectors, or structure if used incorrectly.

Corrosion inspection focuses on prone areas. Check battery compartments, bilges, wheel wells, lavatory and galley areas, lap joints, lower skins, drain paths, exhaust areas, landing gear, control hinges, fasteners, and areas where dissimilar metals meet. Interiors can corrode where moisture is trapped behind insulation or under floorboards. A clean surface is often required before an accurate inspection.

Removal and treatment must follow approved data. Removing too much base metal can create a structural problem. After corrosion removal, the surface may need conversion coating, primer, sealant, topcoat, or corrosion preventive compound. Corrosion preventive compounds include waxy sealants and thin-film products. Selection depends on exposure, access, compatibility, inspection interval, and manufacturer instructions.

Finishing work depends on surface preparation and ambient conditions. Poor cleaning, sanding, masking, etching, conversion coating, mixing, thinning, temperature, humidity, or flash time can lead to finish failure. Fire prevention and ventilation are critical because paints, solvents, and finishing materials may be flammable or toxic. The Safety Data Sheet drives PPE and handling decisions.

Refinishing can affect more than appearance. Identification plates, registration marks, placards, and required markings must be protected or replaced as required. Control surfaces may require balance checks after refinishing because added paint weight can change flutter resistance. A beautiful finish is not acceptable if it makes a control surface out of balance.

Use this corrosion-control sequence:

1. Identify the material, finish system, and applicable maintenance data.
2. Clean with compatible products and protect sensitive areas.
3. Inspect prone locations with adequate lighting and access.
4. Classify the corrosion or finish defect.
5. Remove and treat only as approved.
6. Restore protective barriers and required markings.
7. Document findings and future treatment intervals when required.

For General study, link each cleaning answer to damage prevention. The best answer is rarely the harshest cleaner or fastest abrasive method. It is the method that removes contamination or corrosion while preserving material, finish, structure, health, and airworthiness.