Wallpaper during the Nine Days

Hi,

Although there is no prohibition against putting up wallpaper in the mourning period leading up to Tisha b'Av, one should not do it during shavua shechal bo, the week of Tisha b'Av itself.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 3:82)

Have a great day,
Mordechai