I am going to have to install some recessed wall lights that are about
90mm deep. These will be installed in a cavity wall so total wall
depth is not a problem. Given how close the 90mm depth of the light is
to the 100mm thickness of the inner skin am I likely to encounter any
problems if I just chisel out the whole depth of the inner skin thus
exposing the cavity? The lights do not fix at the rear so there should
be no problem there.

Andrew