Plaster coating (6)
I believe the answer is:
stucco
'plaster coating' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stucco that I've seen before include "White plaster covering for exterior walls" , "Plaster used on external walls" , "Decorative external plaster" , "Outside coat" , "Plaster used for moulding decorations on walls or ceilings" .)