Arrest early aluminium-body corrosion
Blistering or white powder on an Aceca panel is usually galvanic corrosion where the aluminium skin meets the steel body frame; separately, the ash timber in the frame can rot where damp is trapped. Both are arrestable if caught early and ruinous if ignored. This guide covers cosmetic touch-in only — structural frame repair is a coachbuilder's job.
Tools
- Fine abrasive pads
- Plastic scraper
- Masking materials
- Small paint brushes
- Torch
Parts / supplies
- Etch primer suitable for aluminium
- Colour-matched top coat
- Isolation gaskets or sealant for any steel/aluminium interfaces
Procedure
Identify the extent of the blister. Remember the frame beneath the alloy skin is a composite of welded steel tubing and ash timber, so probe carefully at the edges of the affected area.
Stop and consult a coachwork specialist if either the ash timber behind the panel is soft or damp, or the steel framing has corroded through — both are structural and outside the scope of cosmetic touch-in.
For cosmetic blistering only: mask around the area, scrape off the loose paint and white powder, and abrade back to sound clean aluminium with a fine pad.
Wipe with an appropriate solvent and let dry.
Apply etch primer designed for aluminium in thin coats per its instructions.
Apply colour-matched top coat in thin coats, flatting between as needed.
Where the corrosion originated at a steel fixing or a steel frame member, when refitting isolate the two metals with the correct sealant or gasket to slow the galvanic reaction returning.
Warnings
- Do not use bodywork techniques intended for steel: harsh mechanical abrasion, chemical strippers meant for steel, or the wrong primer will accelerate corrosion on aluminium.
- The body frame under the alloy skin is steel tube plus ash timber. If either the ash is soft or damp, or the steel tubing shows structural corrosion, structural repair comes first — do not paint over it.
Related faults
About the author
An independent classic-car enthusiast in North Yorkshire with decades of hands-on experience on British classics — including the AC Aceca — writing the single-model reference he always wished existed. Read the full bio.