What is white rust?
White rust is the powdery white or grey oxide bloom that forms on aluminium, zinc and galvanised surfaces when moisture sits on them without airflow. On aluminium die castings it is aluminium hydroxide, and it appears within days when parts are washed in alkaline cleaner or packed damp.
Also called: white corrosion, aluminium oxide bloom, wet storage stain
- Affected metals
- Aluminium, zinc, galvanised steel
- Common trigger
- Alkaline cleaner above pH 10
- Recommended cleaner pH
- Neutral, 7–9
- Measured rejection change
- 3.2% → 0.4%
White rust is not the same failure as red rust. Red rust is iron oxide and needs iron; white rust needs only a reactive light metal, water and poor ventilation. That is why it shows up on aluminium ADC10 and ADC12 housings, on zinc-plated fasteners, and on galvanised sheet stacked before it is fully dry.
The two most common industrial causes are chemical and logistical. Chemically, alkaline cleaners above roughly pH 10 etch aluminium and leave a reactive, freshly-exposed surface that oxidises fast. Logistically, parts packed while still carrying rinse water in blind holes create a sealed humid pocket — the ideal white rust incubator.
The fix is a neutral-pH cleaner formulated for non-ferrous metals, a clean rinse, and genuinely dry parts before packing. Power Clean's field data on aluminium die-cast housings shows white-rust rejection falling from 3.2% to 0.4% after switching from an alkaline cleaner to neutral-pH NF-14 with a controlled dry.
