Hole in internal breeze block wall - how to repair

Hi guys, I hope you can help. Last weekend I was chiselling out a recess for a new electrical socket in one of my internal walls and through a combination of underestimating the wall thickness and being a little over enthusiastic with the chisel I have effectively knocked a hole through the blocks.

The wall seems to be built of a single layer of breeze blocks about 4-5 inches thick. There is not a hole in it yet but the back of the chiselled out area is loose and I reckon just held in place with the wallpaper on the other side of the wall! Obviously this will now need repairing but I need some advice as to how to fill the hole (in terms of size just think of a double plug socket).

Also for future reference is there a more intelligent way of chiselling out a recess in this type of wall, rather than using a bolster chisel and hammer? It just seems a lot softer material than brick and I need to recess a new light switch in to the same wall

Welcome to the forum.

I suggest raking out all the loose material on the other side of the wall, fixing a piece of expanded metal in the hole and filling with a sand/cement mix; make good after the mortar has dried.

On the side where you're fixing the socket outlet, backfill with mortar to the depth you need to fit the backbox. Carefully drill and plug when the mortar is sufficiently hard.

In future, I suggest drilling to a controlled depth to remove most of the material. A light switch backbox, of course, will be much shallower.

Some of the internal walls in my house have been built of three inch breeze blocks which are very tricky to chase. Recently, I had to fix a backbox using toggle fixings, with the toggles set below the surface on the reverse side of the wall, because there was no depth of material for normal plugs and fixing screws.

Brilliant that sounds like a plan! Just a quick question though - what is expanded metal and how would you actually fix it to the existing blockwork? Sorry for all the questions, just bought our first house in July and trying to do as much of the work that needs doing myself as money is tight!

Thought about posting this in DIY Disasters - I set about trying to guage the thickness of the wall last night in preparation for installing the new light switch (existing one is a pull cord) and realised the wall was a lot thinner than I had previously assumed. I then remembered that when I was drilling the holes for the back box for the plug socket that the drill felt like it was hitting what I presumed originally to be the wall cavity. Sure enough when I inspected the other side of the wall (hidden by the laundry basket) there were 2 rawl plugs sticking through

Expanded metal lathing: galvanised steel mesh.

In a situation like this I would cut a piece oversize for the hole and squeeze it into place, to be held by the mortar when it has set. You could also use some PVA glue around the edges to help with the bonding.

It would be annoying, though, to have to buy a whole roll of it just to cut off the small piece you would need. Any scrap material that can support and help to bond the mortar to the rest of the wall would do.

For the light switch, you will of course need to chase the wall for the switch wire drop, so if you're struggling not to break the breeze blocks you will have to go carefully while you're doing this. Have you considered using a surface mounted switch and mini trunking? Not ideal, I know.

If you have further questions on this, try posting in the UK Electrics forum. Some of the people there can be a bit abrasive, but they mean well and can be very helpful. Be prepared for lots of talk about permitted zones, Part P of the Building Regulations, etc.