How can I repair corrosion around screw holes in the aluminium windows on Grace?
The aluminium window frames on Grace have corrosion around the screw holes, particularly near the catches. Can I clean and fill these areas, and how should I refit the screws to stop the corrosion coming back?
Answer
Repair local corrosion around Grace's window screws by removing all loose aluminium oxide, filling the pits with a suitable epoxy repair compound, then priming and painting the damaged area. First remove the affected fittings and check how much sound metal remains: a weakened catch mounting or badly perforated upper rail needs a mechanical repair or replacement section.
Check beneath the catch
White powder, blistered paint and craters around stainless steel screws usually indicate local galvanic corrosion. Saltwater bridges the stainless steel and aluminium, allowing the aluminium to corrode. Damaged anodising, trapped moisture and leaking screw holes help it spread.
Photograph each fitting before dismantling, then remove one catch or bracket at a time. Support any opening pane before removing its hinges or stays. Wear eye protection when scraping or drilling.
- Shallow pitting: the surrounding rail remains firm, the hole retains its shape and the screw still grips sound metal. A local repair is usually possible.
- Enlarged fixing hole: the surrounding section is sound, but the screw no longer grips. It needs a properly designed fastening repair as well as cosmetic filling.
- Weakened rail: holes merge, the section flexes, cracks appear or corrosion extends beneath the glazing gasket. Remove the frame for assessment and consider replacing the affected extrusion.
Do not keep adding screws alongside failed holes. A row of closely spaced holes can leave the upper rail weaker than the original damage.
Remove corrosion and prepare aluminium
Wash away salt with fresh water and detergent, rinse thoroughly and let the frame dry. Before abrasion, remove grease with a cleaner compatible with the surrounding glazing and seals. Keep acetone and other aggressive solvents away from acrylic panes.
- Mask the pane and rubber seals to protect them from scratches and abrasive dust.
- Scrape away loose coating and white oxide. Abrade the pits with approximately 80 to 120 grit abrasive, using small tools where necessary to reach firm metal.
- Feather the edges of the surrounding coating without unnecessarily stripping intact anodising.
- Remove dust and follow the epoxy manufacturer's final preparation procedure immediately before filling.
Blasting can clean deep craters effectively, but is best done on a dismantled frame by someone familiar with thin aluminium sections. Steel wire brushes and steel grit can embed contamination. Use abrasives intended for aluminium.
Fill pits and restore fixings
A marine epoxy system approved for bonding aluminium is suitable for rebuilding shallow pits. Options include WEST SYSTEM resin with an appropriate thickening filler or an aluminium-compatible metal repair epoxy. Follow the product's preparation, temperature and curing instructions. Avoid ordinary polyester car-body filler.