Piece of artillery that's used by builders? (6)
I believe the answer is:
mortar
'piece of artillery' is the definition.
'mortar' can be an answer for 'artillery' (mortar is a kind of artillery). I'm not certain of the 'piece of' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for mortar that I've seen before include "Brick-joining material or short cannon" , "Bonding for brickwork - small cannon" , "Bond for bricks; weapon" , "Brick bonding mixture" , "Brick cement" .)