Characteristics of the material
Copper has always been considered a noble metal and as such it has also penetrated into the construction industry. Many historical buildings were covered with copper roofs, which have lasted to this day without large modifications. Copper is suitable for its easy shapeability and appearance.
Basic chemical composition and marking
Cu-DPH – 99.9 % Cu, quality marking
CW024A – product marking ... CW024A
If a property typical of the already weathered, coloured copper is demanded (see Life and Corrosion), it is possible to accelerate this process by the application of a chemical treatment.
As a result of exceptional electrical conductivity, copper enters into electrochemical reaction with other metals in wet environments. Due to contact corrosion, metals that touch it are subject to serious damage. Anodised aluminium with an oxidising layer of 20 µm is resistant to water with a copper content. Pure aluminium loses its decorative appearance, but not its function. Direct contact of both materials can be avoided by the application of plastic film. Components from zinc or galvanised sheets must not be installed in the rainwater flow direction, because these metals would become eroded. Steel components should not be installed on the copper either, because corrosion residues make visible stains on the material. Fasteners such as screws, nails or other elements must be solely copper.
Life and corrosion
Because of the weather conditions, the surface of copper sheets erodes and changes colour, first to matt brown, and finally the typically greenish patina. This is a long-lasting process – see the table. The chemical composition of the patina slightly differs depending on the environment, but it is essentially a chemically stable protective layer. The convenience of this process is the so-called "healing" – if a spot in the applied material becomes damaged, the chemical reactions continue, thus creating a new protective layer in the damaged area.