Voids under stone wall (no foundations) - can I fill them and with what if so?

[DIYNotIan]

Hi

We had the roughcast render hacked off the stone wall of our house, and the pointing replaced with lime mortar. There are no foundations. At the time, I pulled back the gravel at the footings of the wall, creating a bit of a trench. There's hard compacted soil beneath the bottom stones. But in some places, there's quite a deep void until you get to the soil (a horizontal void). In the "worse" places, I can get my hand and wrist in there to around halfway along my forearm.

Should I look to fill these horizontal voids before all the gravel gets pushed back into place? Or is it enough to just let the gravel fill them? If I do fill them, what would be best to use? I was thinking NHL lime (3.5?) but also using stones under there to help bind the mortar and to prevent having to use too much of it. But that's a total guess and I'm all ears on what I should use, if indeed anything.

Aside from doing what's right for the building, it does seem that mice are quite keen to scurry their way into the wall (and house) through these deep voids. I've got them blocked with plastic at the moment to stop that. I'd want to make sure whatever I do stops mice getting in.

Pics below, showing the deepest and shallowest sections. And just to be clear, when the gravel is put back to how it was, these voids would be below ground level.

Many thanks

 

[George_engineer]

Fill the void. If you have suitable stone then use that else use a dry mix concrete rammed in.

 

[DIYNotIan]

Many thanks for the reply.

What would be the reason/advantage in using a dry mix?

Yes, I do have some stone. Would you do it so that the front of the stones are:

- Not visible. "Buried" by the concrete so all you can see is concrete at the front (or limecrete if I use that)?
- Visible when finished, and then point around them? So that they pretty much continue the wall down?
- Protruding? Use longer larger stones that are partly in the void and partly sticking our beyond the front face of the wall?

Many thanks

 

[Mr Chibs]

Dry pack mortar is not dry, but not wet like brick laying mortar.

You could using something like 2 to 3 parts grit sand to one part cement.
Mix with water until you can just form a ball with it in your hands, fill the void ramming it in with a piece of wood and a hammer
If the voids are big, yes you can use bits of stone too.

 

[George_engineer]

Dry pack doesn't shrink (or very minimal shrinkage) and will stay in place when rammed in. This is important for void filling. As above, it isn't 'dry' (the cement needs water to cure) but it isn't a flowing concrete.

 

[DIYNotIan]

Thank you both for explaining.

Can you see any disadvantages to using lime (NHL 5?) instead of concrete. It's just that the rest of the wall has been pointed and built in lime, so it would be consistent with that. And would be more breathable than concrete. Any downsides to using it?

Cheers

 

[George_engineer]

If you have NHL5 available then you can use it. I don't think there'd be any advantage over cement in this situation though.

 

[DIYNotIan]

If you have NHL5 available then you can use it. I don't think there'd be any advantage over cement in this situation though.

OK, thanks. How about using NHL3.5 to allow for a bit of breathability and so that it would hopefully move and flex with any wall movements over the seasons and years?

 

[George_engineer]

OK, thanks. How about using NHL3.5 to allow for a bit of breathability and so that it would hopefully move and flex with any wall movements over the seasons and years?

I'd go NHL5 due to being in contact with the ground.

There's no breathability issue here - this is just filling a void to the supporting ground. I also wouldn't expect any significant movement at this location and minor cracking wouldn't cause adverse effect either.

I do spec lime when appropriate (although not to alarm but there are some questions being raised with NHL now... this is horrifying to me as well) but also recognise when other materials might be suitable. The reason not to use cement is that it'll stick very well to the stone but I doubt they'll ever be moved from this position and dry mix isn't quite as sticky anyway.

 

[DIYNotIan]

Hi

Been away for a few days, but hoping to do this tomorrow/Friday.

Just got a couple more questions if you don't mind. Can I just pack the mortar in against the compacted soil? Or do I need to do something to the soil prior to using the mortar?

And is it best to work when the compacted soil is wet or dry?

Many thanks