Hi, My first post here, spo looking for a bit of advice please. I want to cut a hole in a supporting wall in my flat to build in a wall safe. The wall is approx 500mm thick solid brick / masonry and Id like to cut a recess in the wall thats about 400mm wide and goes 400mm into the wall ie not all the way through. Its then my intention to cement a wall safe into the recess. Do I need a lintel above the opening or is 400mm not wide enough to require one, given that my hole wont go all the way through anyway?