Partially filling a hole going straight through breezeblock

[Vadevious]

Currently in the process of renovating a bedroom. It borders the bathroom with a breezeblock wall. Wanted an extra socket at that end, so got my angle grinder and made a start on chasing out the backbox hole. Finishing off with a chisel, I ended up going straight through the wall and into the bathroom (hole broke through behind the bath). So I've ended up continuing until it was all chased out the full way through and went and got a 25mm box instead of the bigger one I was going to use.

Now, I don't plan to renovate the bathroom for a while and this hole can't be seen unless you remove the bath. How can I only partially fill it so the bathroom is sealed off but leaving enough space for my backbox? Had no idea how thin that wall was tbh. Here's a photo of my predicament:

 

[Wayners]

Drill loads off holes in a new block and chip out ready for a new back box.

Fit the block back in with sand and cement

 

[Vadevious]

Drill loads off holes in a new block and chip out ready for a new back box.

Fit the block back in with sand and cement

But that would mean chiseling out even more of the wall to fit a bigger block than the size of the backbox right? Seems like a hell of a lot of faff - surely there must be a simpler, "bodgier" way?

 

[Lower]

If you want to bodge it, screw a piece of wood to the back of the hole (screw through the breeze block into the wood to secure the wood), pack it to the right depth for the backbox with more wood, then fill around the back box with mortar finishing just below the surface and then fill with easifill or similar and sand flush.

 

[Vadevious]

If you want to bodge it, screw a piece of wood to the back of the hole (screw through the breeze block into the wood to secure the wood), pack it to the right depth for the backbox with more wood, then fill around the back box with mortar finishing just below the surface and then fill with easifill or similar and sand flush.

This kinda thing was my thinking tbh. My question is - fill only around the backbox? Or maybe I should just attach the initial piece of wood, fill the hole against the wood up to the depth needed and once dry, remove the piece of wood? Or would that potentially cause problems?

 

[Wayners]

Oh I see now. Sorry. I thought you had knocked out an entire block but you haven't.
Think id put some wood across the back of hole covering hole.
Then...
Tape the back box to a stip of wood.
Now tape the wood either side to the wall so the box is in the correct position floating in hole.
Fill around it and at the back. Do in stages as each mix sets.
When set remove wood and make good surface with filler.
Box will be in the perfect position filled all around

 

[Vadevious]

Oh I see now. Sorry. I thought you had knocked out an entire block but you haven't.
Think id put some wood across the back of hole covering hole.
Then...
Tape the back box to a stip of wood.
Now tape the wood either side to the wall so the box is in the correct position floating in hole.
Fill around it and at the back. Do in stages as each mix sets.
When set remove wood and make good surface with filler.
Box will be in the perfect position filled all around

Thanks!

Some questions though..

I'm confused about taping the backbox to a strip of wood - that really necessary? The hole is the perfect size to snugly fit a backbox already. Could I attack the wood to the back, then throw some plaster to fill out the back up to where the box would end and then just use adhesive to fit the box inside/then fill around it etc? Would I also then be fine removing the original piece of wood at the back once the plaster has set?

Another q - what kind of plaster should I use for the main parts; bonding?

 

[Wayners]

If is snug don't bother with wood.

I'd buy a £5ish mortar mix and just add water.
Put a splash of PVA ( wood glue if you have any) in and will be creamy.
Put that around sides.
Any gravel about. Add a bit to mix to bulk out and wang and the back. Be a concrete mix kind off.

Damp sponge to wipe around as setting. Don't mess with it too much.
Jobs a goodun

 

[Vadevious]

Oooh, mortar mix that sounds like a good idea.

Reason I asked about bonding plaster - I need to buy some anyway as I have a bunch of chases to fill in the room also; but mortar mix does sound like the better option to be fair; thank you. I do have some gravel etc from all the chasing I can use to fill it out a bit also.

Thank you for the advice

 

[Vadevious]

If is snug don't bother with wood.

I'd buy a £5ish mortar mix and just add water.
Put a splash of PVA ( wood glue if you have any) in and will be creamy.
Put that around sides.
Any gravel about. Add a bit to mix to bulk out and wang and the back. Be a concrete mix kind off.

Damp sponge to wipe around as setting. Don't mess with it too much.
Jobs a goodun

Mortar was a genius idea, thanks for the advice - worked out great in the end!