Building an extension and renovating old part of house. How much should I expect to pay for the wet-dash harling on the extension? Bare block at the moment. It is a one and a half storey build, approx 40 sq m of wall with 5 windows and a door. I will be providing materials so it is just the labour and scaffolding costs I need advice on. Also anyone interested in quoting for the work? Post code IV 63.