The corrosion of zinc coatings indoors is much less severe than outdoors due to the absence of rainwater erosion, generally reduced by about four-fifths. The primary cause of indoor corrosion is high air humidity or the storage of unfinished products that are not fully dried, leading to the condensation of a water film on the surface of the zinc coating. According to data, corrosion is most intense when the moisture content in the air reaches 60% and 85-95%. Corrosion is most likely to occur in warehouses during winter. Corrosion typically occurs beneath a thin layer of liquid containing a high concentration of oxygen. Therefore, the corrosion rate primarily depends on the diffusion of oxygen within the moist corrosion layer.
Unlike outdoor corrosion, the corrosion products of zinc coatings indoors are not washed away by rainwater but instead accumulate at the site of corrosion and gradually expand. Consequently, the structure becomes porous, and its volume and weight increase. The corrosion products are strongly alkaline.
In kitchen air, which contains many gases generated from cooking and burning, the corrosion rate is approximately three times higher than usual.
The primary corrosion products of zinc coatings indoors are zinc hydroxide and zinc carbonate.
