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Aluminium

Aluminium tends to be used as a waterproof barrier in buildings because of the slow rate at which it oxidises (rusts). It can be treated to stay nice and shiny for a decade or two and can also be colour coated to last quite well. It’s other attraction in building work is the ease of working it. It is soft and can easily be sawn and drilled by hand. When it does oxidise, due to rain, it gets those greyish green speckles you see on letter box flaps, door handles and window frames. A soft form of aluminium is used in flashings so that they can be ‘dressed’ to fit uneven surfaces around slates, tiles, masonry etc.

The down side to aluminium is the very large amount of electrical energy needed to produce it. Typically the ore, bauxite, might be mined in Australia, shipped to Iceland where some surplus hydro-electrical energy might be available to turn it into aluminium and then shipped to a factory somewhere else to be extruded into sections. Then it will be shipped to other countries for sale. The embodied energy incorporated into making virgin aluminium is around 155MJ/kg. It is truly one of the great energy gobblers and it also suffers from the typical pollution problems associated with heavy industry such as the recent ecological disaster in Hungary.  (As a slight defense of the material, it recycles well !)

Another down side to using aluminium in building work may be its very good conductivity of heat. Used in the wrong situation or position (such as structural framework) it may become a thermal bridge and allow heat to escape from the house.

Probably its best uses in building work is as a flashing material instead of the more polluting lead or where it provides a thin external cladding to timber windows, particularly the sills. Little of the material is used and it may protect the timber beneath extremely well.

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