The internal walls in my 1960s house are all built of red coloured, hollow blocks which are very hard. I always have to faff about when fixing to them - sometimes you drill into a solid bit, other times a hollow bit, so you end up messing about with different fixings. Sinking back boxes for sockets are a nightmare - it's not deep enough if you don't cut into the block, but if you do, the hollow bits are too deep, then there's hoizontal solid bits to cut out.
I don't know the name for these blocks, but does anyone have any advice on how to work with them?
Peter.