On Monday, 19 February 2018 18:42:06 UTC, ARW wrote:
Stitch drilling and or SDS chisels are the only methods I have found
successful on hard brick. And even then you sometimes just have to bond
in the back box (old bonding and a bit of cement) as the brick collapses.

I chuck the rubble back in mixed with a bit of PVA and multifinish when I find I've inadvertently knocked through to the next room.

Learnt the hard way not to use foam in such applications.

Owain