Patination process / Condensation
NedZink Natural (natural zinc)
NedZink NATUREL is a durable and aesthetic material that in the course of time develops a unique charm by the progressive patination of roof and façade cladding. The patina layer originates by the formation of a zinc carbonate base, which forms an oxide skin that is also a natural protective coating. This process starts under the influence of the weather conditions. It has a natural course, so the full grey shade is obtained after one to four years.
Zn + O2 => ZnO + H2O => Zn(OH)2 + CO2 => ZnCO3
zinc + oxygen => Zinc oxide + water => zinc hydroxide + carbondioxe => zinc carbonate
The exact composition of the patina partly depends on the environment in which the layer is formed. In the ‘normal’ outer atmosphere, we are dealing with a number of additional factors such as:
– precipitation: rain, snow, hail, fog, condensation
– air pollution:
* emission of a wide variety of chemical substances caused by industry, traffic etc.
* sea salt in coastal areas
* sand and dust, which are carried by strong winds
All these factors are, depending on the geographical location, present in several variations in our atmosphere and in combination with each other have a more or less significant influence on the degree of corrosion or wear. The decrease in thickness of the material is dependent on the environment, namely, rural, urban, industrial and coastal and combinations.
When zinc is used in coastal areas, the surface is exposed to salt air. When bright-rolled zinc is used, the patina layer will form normally when an adequate supply of water is available. For parts that are not immediately watered and are therefore dependent on moisture in the air, the patina process is slower. This is shown by the erratic discoloration of the material and the longer period before the patina is built and a uniform light gray color occurs. The combination of salt air and lack of direct rainwater results in discoloration on the surface. These visual effects are inevitable and irreversible.
NedZink NOVA (prepatinated zinc)
NedZink NOVA is NedZink titanium zinc that undergoes a patination process to give a fully natural colour. The uniform medium-grey surface of NedZink NOVA originates after a chemical surface treatment following the rolling process. No coating or lacquer layer is applied. The structure and composition of the patina layer that is normally naturally formed by weather influences is simulated, and the natural properties of the titanium zinc are fully retained. Because NedZink NOVA is mainly used for aesthetically high quality applications, e.g. for façades, the products are provided with temporary surface protection. This protection prevents minor damage and soiling during processing and assembly, and ensures an optimal appearance after application.
Condensation / moisture
The patina layer may be affected or even dissolved by different causes. A possible deterioration of the patina layer may be caused by white rust. This form of corrosion occurs mainly on the backside of the zinc. Exposure to moisture leads to the formation of zinc hydroxide (white rust). Continuous wet, humid conditions without the benefit of freely circulating air are associated with such problems.
In a standard construction build up the difference in vapour pressure (internal and external) causes vapour to be transported through the structure from the inside to the outside. It condenses at the backside of the zinc surface. An excessive build up of condensation leads to serious degradation of the zinc, especially when no patina is present. Normally the patina layer is formed when the air is able to flow between the apertures without major obstacles. When zinc is applied on a hot roof construction there are special demands concerning corrosion.
NedZink NOVA Pro-Tec is processed with a protective coating on the backside for application on either cold or hot roof constructions. This protective coating consists of a 2-layer polymer coating system protects the zinc against the effects of water vapour and other substances. Pro-Tec can be used in all standard systems, but is mainly recommended for unventilated, damp-proof hot roof constructions and outer wall cladding.
(Fiber cement) slate
If zinc is used in combination with other materials, some materials cause damage to the zinc. It is recommended when (fiber cement) slates are placed above the zinc to contact the supplier of these slates. When possible negative effects are ruled out, the lifetime of the zinc is guaranteed.