Reddish-brown stains on the paint surface.
Causes:
The nails have not been galvanized;
Non-galvanized nail heads have not been primed;
Galvanized nail heads have been damaged during polishing or during hammering.
Solution:
If you are painting a new façade where non-galvanized iron nails are present, first prime the nails with metal primer. For nails that are already rusty, the rust should be removed by polishing, then they should be primed and the surface should be fully or partially repainted. Use galvanized nails.