Materials for cladding are chosen for their cost, manufacturing parameters, durability and appearance. linear cladding

The most commonly used materials are steel and aluminium. Stainless steel and weathering steels are also reasonably available. In particular circumstances other materials such as copper, bronze and titanium have also been used.

Steel and aluminium are used extensively in all of the three classifications of metal cladding types. The principal differences between the two lie in the strength, durability and cost of each material. james hardie

Steel used in cladding is normally pre-galvanised and pre-painted in coil form prior to panel manufacture. During the galvanising process the steel is dipped into molten zinc or zinc-aluminium alloy (55% aluminium and 45% zinc) and a layer of the metallic coating is bonded to form a hard, durable outer layer. The thickness can be varied and is usually expressed as the weight of zinc or zinc-aluminium per square metre of on both sides of the sheet. Typically the minimum coating weight on cladding is panels is 275g/m2 for zinc and 255g/m2 for zinc-aluminium. The zinc-aluminium alloy (Galvalloy) has slightly better durability in polluted or coastal environments and improves "cut edge" corrosion performance on premium pre-finished metals like HPS200 by Corus. The steel is then coated with a variety of finishes for both improved appearance and durability. The premium coating for Corus products is HPS200. It is a 200 micron thick organic coating which provides a tough and durable coating. Normally the most onerous environmental conditions exist on the outside of the sheets. However the underside of the sheet may be subjected to condensation and trapped moisture, it is therefore normal apply a coating to this face, at various specifications to suit both cost and environmental conditions. Aluminium Composite Panel Cladding System

Aluminium is naturally more corrosion resistant. Bare aluminium reacts rapidly with oxygen to form a hard, dense layer that inhibits further corrosion. Aluminium used in cladding is generally in form of an alloy with magnesium and manganese. Further details are available in the relevant British and European standards. Normally aluminium (known as mill finish) has sufficient durability on its own but where necessary durability can be improved by adding an organic or metallic coating. Aluminium Cladding for Commercial Buildings

Comparing the relative merits of steel and aluminium can be difficult and much often depends on the particular circumstances. Aluminium is inherently more corrosion resistant than steel although painted steel is durable. Aluminium is lighter but not as strong, therefore profiles have to be deeper or thicker to span the same distances between purlins. Greater quantities of energy are used in the production of aluminium than steel making it more expensive than steel. Steel it more resistant to impact and moves less than aluminium when subject to temperature changes. It also tends to perform better in fire, having a much higher melting point.