Hello there!

We are just getting our whole house rewire finished and will soon be able to fill up the chases for the new wires. Our house is a 1910 Victorian build type and has 4 different types of walls. I am wondering what's the best material to fill the voids?
They are all about 25mm deep x 65mm wide, the wires are enclosed in oval conduits. I will describe below what each wall is according to the enumerated picture :D

1. External solid brick wall plastered with lime (probably mixed with ash, hence the dark grey). Will be insulated with wood fibre boards so the finish is not important at this layer but it needs to breath.

2. Internal solid wall. It seems to have clay (?) breezed blocks. Plastered with lime as the external walls. The finish is important here as we would like to remove the wallpaper around it, fill some holes, sand and paint it with clay paint.

3. Internal stud lath and plaster wall. The plaster is also lime. Finish is important on this one too.

4. External wall of modern-ish extension. It seems to be a cavity wall with breeze blocks plastered with gypsum. Finish might be important as I am unsure how this will be insulated (maybe in the cavity, but haven't gone into it yet).

I don't mind having to work extra with lime materials for 1, 2 and 3 that take longer to set as long as we make it good with the best materials we can and closer to original. When it comes the time to plaster the external wall WF boards I will probably use limegreen solo, but I am wondering what's best for these smaller jobs. As for 4, I suspect that's a job for gypsum based materials?

Thanks in advance!

Posted By: bgasparotto1. External solid brick wall plastered with lime (probably mixed with ash, hence the dark grey). Will be insulated with wood fibre boards so the finish is not important at this layer but it needs to breath.

If you are covering the wall with wood fibre boards why bother filling the chasings, just put the insulation over.

For the remainder I would fill with a far as possible the same material as the original wall. This will ensure that the filling and the original will behave the same with follow on decorations.

Personally, I've always used "bonding", which is a sticky, oatmeal texture. Most merchants stock it. Same reasons as Tony mentions.

Thanks for all the advice!

Posted By: djhYou don't need to worry about breathability over a small area such as this chase.

That's the bit that always seem to get me! I don't have enough experience to make such calls, so I end up trying to follow breathability almost religiously but probably end up creating more work for my self.

Regarding filling the chases, as Tony said I would also be a bit concerned with air leaking into places it shouldn't, that's why I still want to fill them before insulating :)

I do have some NHL 2 (would that be an issue, Mike1?) laying around and my in-laws have some spare lime putty (for the L&P wall), so I am considering give it a go with lime where there is already lime, then go with the "bonding" for the extension as suggested.

Posted By: Mike1And with all lime use, do use the appropriate PPE, including safety specs & mask when mixing.

Thanks Mike! Good shout about the PPE. I have a decent mask and goggles and some eye wash (https://www.limestuff.co.uk/protection/eyewash) in case things still go south!

given that

Posted By: djhYou don't need to worry about breathability over a small area such as this chase.

and that you want to put something in the channels to ensure air tightness then perhaps the pragmatic approach is to use what ever you have to hand without the need to go and buy something.