Craftsman's expression of astonishment, wiping bottom and, simultaneously, leg (10)
I believe the answer is:
stonemason
'craftsman's' is the definition.
(stonemason is a kind of craftsman)
'expression of astonishment wiping bottom and simultaneously leg' is the wordplay.
'expression of astonishment' becomes 'stoneme' ('stone me' is an expression of surprise).
'wiping bottom' means to remove the last letter (the final or bottom letter is erased).
'and' says to put letters next to each other.
'simultaneously' becomes 'as'.
'leg' becomes 'on' (cricket term, fielding positions).
'stoneme' with its final letter taken off is 'stonem'.
'stonem'+'as'+'on'='STONEMASON'
(Other definitions for stonemason that I've seen before include "Monumental worker" , "Construction worker" , "Building worker" , "chipper?" , "manual worker" .)