Recognising corrosion on an aluminium boat

Do not immediately clean or grind away a suspect area. Its original pattern, location and relationship with fasteners or moisture provide important evidence about the cause.

1. Recognise signs that need attention

Look for white or grey powder, rough pits, crumbling edges, paint blisters, dark moisture traces and attack around welds or fasteners. A thin uniform colour change is different from local material loss.

Use good light and take both overview and close-up photographs with a size reference. Record whether the area is dry, wet, exposed to salt or recently cleaned.

2. Look for contact with other metals

When aluminium is electrically connected to a different metal in a conducting liquid, galvanic corrosion can occur. Fasteners, fittings, wiring, shore power and the water environment may all form part of the system.

The most visible component is not necessarily the cause. Do not remove insulating washers or bonding components until their material and purpose are understood.

3. Inspect coating and edges without opening them

Corrosion beneath paint or coating may appear as blisters, lifted edges or discolouration. Moisture can travel further beneath the coating than the exterior suggests.

Do not puncture a blister for a photograph or sand it clean before deciding the extent and repair method. That removes evidence and exposes more unprotected metal.

4. Record water, salt and trapped moisture

Salt, contaminated water and persistent moisture in crevices increase exposure. Inspect drainage, the bilge, joints and places where dirt or wet material remains against aluminium.

Rinse only in accordance with suitable care instructions and allow the area to dry. Recurrent moisture can indicate a leak or design detail that needs addressing with the corrosion.

5. Consider anodes and the electrical context

Sacrificial anodes form part of a balanced protection system. Very unusual wear, no apparent activity or an unsuitable material can justify a check, but appearance alone is not a full diagnosis.

Do not change anode material, shore-power earthing or bonding by guesswork. Measurements and knowledge of the water and installation are needed to assess an electrical cause.

6. Decide whether cleaning, repair or replacement fits

Surface deposits, deep pitting and attack on a structural or watertight part require different responses. Thickness, function, access and extent determine whether cleaning, repair or replacement is appropriate.

Also read repair or replace an aluminium boat part. Send views of the complete assembly, adjacent metals and both sides where safely accessible.

Frequently asked questions

Is white residue on aluminium always corrosion?

Not always. It may be a deposit or light oxidation, but powder combined with pitting, moisture or another metal needs further investigation.

Can stainless steel cause aluminium corrosion?

Contact between dissimilar metals in a wet conducting environment can promote galvanic corrosion. Isolation, surface area, electrolyte and material ratio all matter.

Should a paint blister be opened?

Not without a repair plan. Record it first and assess extent and cause to avoid unnecessary damage and trapped moisture.