I want to install a shower and conceal the 15mm copper cold water supply pipe behind the tiles (at low level) and behind the plaster (at higher level). If I channel out the plaster, insert the pipe, then plaster over the pipe, should I put something over the pipe first (like you do if you're plastering over cable), and if so, what? I'm concerned that any expansion or contraction in the pipe will crack the plaster.