Filling electrical chases in solid walls

[mostly_wrong]

Hi all,

Apologies for starting a new thread I think similar ones are dotted around but i'm quite new to this and don't know if i'm reading that advice properly.

Recently bought an 1880s semi, there are many like it but this one is mine. Solid walls of very soft red brick, and from what I can tell it's mostly lime plaster with a few patches of something else. The gable wall has been soaked over the years thanks to dodgy roofing which is now remedied. I've just had the house rewired leaving lots of beautiful large chases in the walls or around 4cm deep in some places. On the damp walls they've had to use lots of foam to secure the new boxes. Old boxes have been left in place too which I want to pull out and fill.

• What's the best thing to fill these chases with? All the advice outside of this site seems to say use bonding, but I think that's not so good for these walls? Should I use anything different on the external walls?
• In many places the conduit is quite tight in the chase. Very noob question but what's the best way to get behind it, or should I just be pressing whatever filler in as deep and firmly as possible?
• To fill the old disused electrical back boxes I assume it's best to try and use an old brick to fill the void?

I did say I was new to this! For full transparency i've used a weak pva mix (about 1:5) to try and limit the dust, although I now realise that's not great.

Would really appreciate any advice for any of the above, thanks!

 

[aockenden]

There are tons of options. Hemp + NHL (2 or 3.5) is great for filling deep stuff anywhere inside the house. Not suitable for use on the outside of the house. It should be very breathable and will harden to a good depth relatively quickly. Although if the wall is still damp you would be well advised to wait until it's mostly dried, as the hemp can mold if it can't dry out because the substrate is still soaked. Leave it a few mm shy of flush with the surrounding plaster. Once it's nice and firm you can skim with a fine lime plaster mix to make it flush with the surrounding plaster. I definitely wouldn't try to get any plaster behind the conduit, just compact your filler material into the gap and let it find it's way back there.

 

[Zebra]

Breathability isn't really a concern given that it's such a small area. Agree with the above about not worrying too much about getting it behind the conduit and about leaving the filler a few mm short of flush to leave room for some topcoat. You could use some ready-mixed lime plaster, or make some up using some hydrated lime available from builders merchants (make it into putty first and let it sit for a bit ideally then mix with sand - it may not be the best strongest stuff but it'd do for what you want).
You could use the same stuff for filling the backboxes, although maybe do it in a couple of layers as 35mm thick or whatever is probably too much in one go.

 

[mostly_wrong]

Brilliant, thank you both