Large areas of paint peeling off the hot-dip galvanized steel sheet roofing. It is necessary to paint the roof. Please list the necessary steps for painting the roofing. These steps are as follows:
1) complete removal of the old coating by scraping it off;
2) cleaning with an ammonia-based surfactant, thorough sanding with abrasive fleece, and then thoroughly rinsing with clean water;
3) base coat with epoxy varnish;
4) top coat with 2-component polyurethane resin varnish.

Due to the anticipated high chemical loads, 2-k materials were selected here. Epoxy varnishes are characterized by exceptionally good adhesion, but under the influence of weather conditions they tend to chalk. For this reason, the top coat is made of polyurethane varnishes.

What materials should be used for coatings on zinc or galvanized steel sheets, if the old coatings on them adhere well to the substrate?
In the case described, a new coating must be applied to the old paint. Best, if the same materials are used in the new coating, what in the existing shell. If the type of binder in the old coating cannot be identified, it can be painted with dispersion varnish without any risk. However, it should be remembered, by performing e.g.. roof coatings, with increased water absorption of these materials.