Wall plaster (6)
I believe the answer is:
stucco
'wall plaster' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stucco that I've seen before include "White plaster covering for exterior walls" , "Plaster for coating outside walls" , "wall-covering" , "Fine type of plaster" , "Fine decorative plaster" .)