Copper
Copper is a material that can be used in its pure form or alloyed with other materials e.g. brass, where it is combined with up to 50% zinc, or bronze where it is combined with tin. Copper used in the construction industry tends to be in the form of tube, strip, sheet or bar. Woven copper wire is rarely used. Sheet material is most commonly used.
The basic copper material is very soft and ductile and is hardened by cold working, hence it can be easily formed by hand or machine. After cold working it can be heated and this will restore its softness or ductility.
Traditional roof cladding employs the long strip method of assembly, using long sheets of soft copper with standing seams or batten roll joints along the length and welts for the short joints. Soft or annealed copper also tends to be used for flashings.
Half-hard copper can be used where some rigidity is necessary however this allows less scope for working the material without heating. The beauty of copper is the range of natural and artificial patina’s that can be developed on the surface. The natural patina is a pale mottled green or blue/green shade. A vast range of artificial patina’s can be developed using chemical ingredients to produce a wide range of colours with varying stability.
Copper is too valuable to be thrown away. It also suffers virtually no loss in its properties or performance when recycled, and easily reintegrated into the production cycle. At the moment just under 50% of copper used in Europe is now coming from recycled material. Recycling of the material uses up to 85% less energy than primary production.
High grade copper (electrical grade) should not be mixed with low grade copper (e.g. plumbing pipe), as too much phosphorus in the latter reduces electrical conductivity.
Also, high grade scrap has 95% of the value of primary copper.
Copper prices vary, like most other metals and alloys (such as stainless steel). However, these prices fluctuate according to availability, mining company investment and control of quantity available.
There is no reason why copper should not be available for centuries to come. Socially responsible mining and recycling should ensure this, and in doing so limit environmental damage associated with copper.
Points to watch
Copper comes in a variety of grades (alloys) and hardnesses. It is important to select the appropriate grade and hardness for the particular application.
The patina can be allowed to develop naturally or it can be accelerated or induced immediately. It can be applied as a factory coating.
When copper is left to its own devices, the colour sequence is natural copper, dark brown, black, green spots, light green covering, and green blue patina. This process may take from 2-10 years.
The patina is not a stable coating when it is allowed to develop naturally. The patination will vary according to the angle of the surface, the exposure to prevailing weather conditions and the orientation of the surface (look at any church roof). If a uniform colour is required, don’t use copper!
Copper can be preserved in its natural colour by surface coating.
The patina will mark when scratched, however, it is self-healing. There are claims from manufacturers that surface sealers are available to encapsulate and protect the patina. This, however, contradicts the nature of the material.
Copper is a “noble” material so it must be used with care to avoid bi-metallic corrosion. It is important that the fixings are of an equivalent or more ‘noble’ material. The copper should be isolated from materials of a less ‘noble’ composition.
Caution is necessary in respect of thermal cycling. Copper sheet must be free to move with thermal cycling, hence it should be used with dry rolled or standing seam joints that permit movement throughout the length of the material from one fixed point. It is also important to incorporate an under felt to assist the movement of the copper and prevent wear from thermal cycling.
Mid Line Vents (JLE): Culling Road Shaft
A 2mm C106 half-hard copper sheet material manufactured in pre-assembled panels on a stainless steel horizontal rail system fixed to a galvanised steel support structure. The cladding is formed in a series of horizontal bands that wrap around the vent shaft surface structure. The panels are bolt fixed to the steel structure and the copper is riveted to the stainless steel horizontal rails. The material was patinated on site.
A 1/4 hardness 0.6mm copper sheet long strip horizontal standing seam cladding with welted vertical joints fixed to a timber board substrate. Openings are formed with stainless steel aprons. The copper is being left unsealed to patina naturally.
Prefabricated rain screen cladding panels formed in copper sheet riveted to stainless steel horizontal rails. The material will be pre-patinated and will incorporate stainless steel mesh panels for ventilation intake/extract zones. The copper will be fixed with tamper-proof button head screws. A high degree of precision will be achieved by C+C cutting and factory assembly process.
The Spire’s base is a 7m diameter disc of bronze, machined with a logarithmic spiral.
Plymouth Theatre Royal Production Centre TR2
Substantial areas of the external walls are made of woven phosphor bronze — essentially a copper cloth.
