Just started chasing the cable runs and sinking back boxes with SDS box
sinker and wheel chaser. (works a treat) howver the blocks are GP1's
(4" hollow) so when I sink the boxes I'm left with a deeper hole than
required due to the cavity in the block, do I simply pack back out with
sand/cement? and also is it OK to "glue" the galvenised back boxes into
place or do they require a mechanical fixing. I'd prefer to glue them
as drilling and fixing to the sand and cement would not hold very well
I would have thought.

Cheers