Contact With Other Building Materials

Whilst dry cement-based materials do not attack aluminium, the alkalinity of wet cement, concrete and mortar causes rapid corrosion. Thus, where these materials make contact during the construction process, the metal should be protected by a coating of bitumen paint. Furthermore, anodised and particularly coloured sections, such as glazing units, can be permanently damaged by droplets of wet cement products, and should be protected on site by a removable lacquer or plastic film. Under dry conditions aluminium is unaffected by contact with timber; however, certain timber preservatives, particularly those containing copper compounds, may cause corrosion under conditions of high humidity. Where this risk is present the metal should be protected with a coating of bitumen.

Although aluminium is highly resistant to corrosion in isolation, it can be seriously affected by corrosion when in contact with other metals. The most serious effects occur with copper and copper-based alloys, and rainwater must not flow from a copper roof or copper pipes into contact with aluminium. Except in marine and industrial environments it is safe to use stainless steel fixings or lead with aluminium, although zinc and zinc-coated steel fixings are more durable. Unprotected mild steel should not be in electrical contact with aluminium.

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