Car, motorcycle and boat decals can be applied in any smooth surface as long as it’s clean of dust, grease and chemicals.
Wall decals can be applied in any smooth wall also clean of dust etc. and even on mildly grained walls.
They cannot be applied on walls that:
a) Have a high humidity concentration
b) Are painted with silicon-based paints (eg. Anti-humidity paints, anti-mold etc.)
c) Have fuzz (e.g. Velvet)