In the tank of the new sewage treatment plant, the built-in and already primed steel elements were intended for painting. About 10% the surface of steel elements shows corrosion. The coating must be resistant to the effects of wastewater with a pH value of 1. Please list the necessary painting activities and justify their choice.

These steps are as follows:
1) oszlifowanie powierzchni żużlem wielkopiecowym;
2) zagruntowanie farbą epoksydową z dodatkiem pyłu cynkowego;
3) powtórne zagruntowanie farbą epoksydową z dodatkiem pyłu cynkowego;
4) pierwsze pomalowanie kryjące lakierem poliuretanowym;
5) drugie pomalowanie kryjące lakierem poliuretanowym;
6) zalecana grubość powłoki wynosi min. 300 µm.

The old coating shows a corrosion degree of approx. 10%. Due to the expected chemical loads, the old primer should be sanded down. Because sand cannot be sanded for health reasons, grinding with slag is used. Epoxy resin provides the varnish with very good adhesion. Zinc dust protects well against corrosion. Polyurethane varnishes are completely acid-resistant.
A minimum coating thickness is provided for such a high chemical load 300 µm.