The corrosion of zinc coatings indoors is much lighter than that outdoors due to the absence of rainwater washing, generally reduced by about four-fifths. The main reason for indoor corrosion is high air humidity or the storage of unfinished dried products, resulting in 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 generally occurs under a thin layer of liquid containing a lot of oxygen. Therefore, the corrosion rate mainly depends on the diffusion of oxygen in the wet corrosion layer.
Unlike outdoors, where corrosion products of zinc coatings are washed away by rainwater, indoor corrosion products form deposits at the site of corrosion and gradually expand. Consequently, the structure becomes loose and porous, increasing in volume and weight. The corrosion products are strongly alkaline.
The corrosion rate in kitchen air, which contains many gases generated by cooking and burning, is about three times faster than usual.
The main corrosion products of zinc coatings indoors are zinc hydroxide and zinc carbonate.
