ᐅ Concrete walls cause rust stains on wallpaper; new construction;

Hello everyone,

we are currently building a semi-detached house. During an inspection, I noticed rust stains appearing on the wallpaper near the concrete columns. I suspect this comes from the tie wire, as the reinforcing steel is not visible. I want to be prepared in case I need to make a complaint. Should the concrete wall have been treated before wallpapering, or is it acceptable in an emergency to simply repaint the wallpaper, hoping that no further rust will appear under normal indoor humidity? Unfortunately, complaints are not always successful with our general contractor.

Thank you very much for your support!