Seen in pebbledash, large piece of masonry (6)
I believe the answer is:
ashlar
'masonry' is the definition.
(I've seen this before)
'seen in pebbledash large piece' is the wordplay.
'seen in' indicates the answer is hidden within the clue.
'ASHLAR' is hidden in the letters of 'pebbledash large piece'.
'of' is the link.
(Other definitions for ashlar that I've seen before include "Dressed stone for facing (A, not E)" , "building material" , "Rectangular block of cut stone" , "Large square-cut stone" , "Rash Al could produce cut stone" .)