The norm PN-EN 508 – 1.2010 defines the minimum requirement of 275 g/m² zinc coating for such roof coverings. On top of the galvanization there are different types of lacquers available for use, which, together, determine the coating’s final scratch resistance.
Steel sheet roofing materials coated in gloss or matte polyester typically have inner lacquer layers measuring between 27-38 µm. They are considered “thin-layered coatings” and are generally covered by a written guarantee of 10 years.
However, the most highly recommended types have “thick-layered coatings” with an inner lacquer layer 50 µm thick, which gives the steel sheets greater resistance to corrosion and mechanical damage. These high-quality products, such as those provided by the Polish manufacturer BUDMAT®, can be warranted for 30 years.
A characteristic of these sheets is their increased resistance to the kinds of frictional strain to which a roof is often subjected, such as frozen snow, or during assembly. The surface layer contains polymeror ceramic grain which prevents surface scatching.
During the manufacturing process the coated steel sheets are measured with the PHASCOPE® PMP10 DUPLEX. This instrument uses two different electro-magnetic measurement methods to determine the thickness of the paint and zinc layers in a single measurement process and displays the results separately: The magnetic induction method is used for measuring the overall thickness of the paint and zinc on top of the ferrous base material, whereas the phase-sensitive eddy current method is employed for measuring just the zinc coating, irrespective of overlying paint layers. The thickness of the paint layer is calculated automatically as the difference between these two results.