May be repeating ourselves as first post and unsure! Just converted bathroom from 2 v.small rooms into 1 just small room.Fitted new toilet, sink and p-bath.Bath fits snugly between two walls.Had to change end of taps around due to P shape and lack of space. However end where taps was was outer wall and now is inner wall.No problem there BUT can't fix mixer bar of thermostatic shower onto this wall as it is inner wall and under the (currently) crumbling plaster are thin breezeblocks and part breezeblocks. We need about 3-3.1/2 inches to be able to affix the mixer bar. Apart from removing plaster and building wooden frame on breezeblocks to support a small wooden box which in turn would hold mixer bar screws/fittings, water pipes coming up into box, and then be tiled over etc., any other suggestions. To recap, mixer bar with fittings/screws needing about 3-3.1/2inches. Wall - thin singular breezeblock inner wall. First big plumbing DIY job. Determined to do it right. Any suggestions please folks???