Metal sheets stored too long in improper conditions undergo scorching, the efffect of which is local coming off of varnish layer, and after oxidizing in these places, the steel core becomes exposed and its advancing corrosion starts (slowed down thanks to the cathodal cover of the zinc coating).However, clients very often cannot understand why it happens like that, if the metal sheets on roofs are exposed to similar conditions, ie. snow, rain, temperature changes, sun and they do not undergo scorching.
The difference is that metal sheets on the roof dry instantly while a metal sheet put on the next one, after getting moist between the sheets as a result of steam condensation, or folded already wet, will never be dried (analogy in case of storing boards).
Therefore after some time the varnish will be discolorated (visible white powder). It is the effect of so-called white corrosion.
In order to avoid this it is necessary to:
If there is a need to store metal sheets by a longer period of time term / max. 3 months/ :
- Definitely, up to 2 weeks, it is necessary to remove the protective foil: exposing products with the protective foil to the solar radiation as well as moist may cause damages to the varnish cover and problems in removing the foil or remains of glue.
- During the storage it is necessary to protect the products against rapid changes of air moist and temperature, which cause the condensation of steam. The negligence in this scope can lead to the appearance of white spots / galvanized sheets/or black ones /aluzinc sheets/ and damaging of the varnish cover/ coated metal sheets. Therefore, the material must be stored in dry and airy rooms, without any neighbouring aggressivly reacting materials, without exposing the metal sheets to the direct effect of sun and water /the possibility of sheet scorching /.
- It is necessary to separate material from the base by minimum 20 cm.
- It is necessary to interleave every sheet with thin distance dividers, or to place in a standing position e.g. by the wall.
- If there is a need of locating the metal sheets in the open area for a short period of time (for the duration of assembly work) a slope along the sheet must be guaranteed– carrying away the moist.
- Basic airy cover must be applied.
- The whole sheets dry must be kept dry.