Fill Existing Cavities in Old Stone Wall

[SimonLePine]

Hi All,

I've done a bunch of Googling but can't find any specific answers to my problem/question.

I'm repointing some stone walls. It's all going well but having removed old pointing in some areas I'm discovering large cavities within the stone wall. Where possible I'm fitting correct sized stone to fill the holes and pointing around the stone.

In some cases though, there can be a small hole in the wall leading to a larger cavity inside the wall. I would think plugging those holes simply seals an air pocket in the wall.

I'm thinking I have 5 options:
1.) fill large cavities with cement - bad idea since cement won't let moisture out.
2.) fill large cavities sand - run the risk of the sand flowing through a hole and out lower in the wall.
3.) fill large cavities with gravel.
4.) fill large cavities with left over lime mortar rubble.
5.) cover the hole and leave the cavities unfilled.

I moved here from Western North America so that makes me a little paranoid about houses shifting and earthquakes. My thinking is if I fill cavities somehow then if the stones do ever shift it's a movement of 1-2mm rather than the entire in hole if left unfilled.

It seems logical to me to fill with either gravel or old lime mortar rubble. The larger pieces are more likely to seal small hikes and less likely to flow out as sand might.

Is this the best approach? Or is it a bad idea? Any downside or upside to doing it this way? Or any better options I haven't thought of?

Thanks!
SL

 

[jj4091]

https://www.screwfix.com/p/soudal-a...A_alqKhvspNA78WwU-0aAtr3EALw_wcB&gclsrc=aw.ds maybe?

 

[SimonLePine]

https://www.screwfix.com/p/soudal-a...A_alqKhvspNA78WwU-0aAtr3EALw_wcB&gclsrc=aw.ds maybe?

Thank you, yeah I thought of that stuff too.

I can't imagine it's very permeable so is that not the same as putting concrete in the hole?

 

[RandomGrinch]

What sort of stone wall is it?
Posting a photo of it, may help us understand better.

For instance, this may not be the same as your case, but I live in a town full of Victorian terraces - the house walls have a small rubble filled cavity between two 'finished' rough stone faces.
The walls are full of voids, but unless there is a particular issue, it isn't a problem; the place seems pretty solid after 135 years!
If there are no issues with the wall, just keep doing what you are doing; repoint with lime mortar, fill in the larger holes with appropriately sized stones, and the smaller holes with mortar.
You may need to take care if you have any work done on the wall, i.e. to cut a new opening, or core a hole - if you're not careful, a load of rubble may fall out of the new hole, destabilising the wall.

 

[jj4091]

Thank you, yeah I thought of that stuff too.

I can't imagine it's very permeable so is that not the same as putting concrete in the hole?

Probably but I thought it would be easier the trying to get concrete or mortar in there.

 

[Ivor Windybottom]

Get a mortar gun, squirt it in as best you can. If it looks right then it's fine.

Relax, loads of walls have air voids in them, perforated and frogged bricks don't always get filled.

 

[SimonLePine]

What sort of stone wall is it?
Posting a photo of it, may help us understand better.

For instance, this may not be the same as your case, but I live in a town full of Victorian terraces - the house walls have a small rubble filled cavity between two 'finished' rough stone faces.
The walls are full of voids, but unless there is a particular issue, it isn't a problem; the place seems pretty solid after 135 years!
If there are no issues with the wall, just keep doing what you are doing; repoint with lime mortar, fill in the larger holes with appropriately sized stones, and the smaller holes with mortar.
You may need to take care if you have any work done on the wall, i.e. to cut a new opening, or core a hole - if you're not careful, a load of rubble may fall out of the new hole, destabilising the wall.

Thanks again (to everyone). And sorry for the delayed response, working on a tech startup, a full time job, and a massive renovation is proving a bit much.

This is the wall and the voids I'm looking at. Some of them go back 12in or more. So I'm definitely not getting mortar in via normal pointing methods.

As someone said, maybe a mortar gun is the right way to go.

I think it makes sense to fill any air gap with supporting material while I have the opportunity since we plan to be in this house for 20+ years so I'd prefer to do it once and do it right.

 

[RandomGrinch]

This is the wall and the voids I'm looking at. Some of them go back 12in or more. So I'm definitely not getting mortar in via normal pointing methods.

Thanks for the pictures.

Similar to my wall - no need to worry about the voids, or unnecessarily fill them. That's just how they were built.

IMHO, there's the possibility of causing issues, if there were to be too great an intervention.

It looks like it will clean up beautifully, with some repointing with lime mortar - a nice feature wall?

A small section of my wall, copied from another thread...

 

[SimonLePine]

Thanks for the pictures.

Similar to my wall - no need to worry about the voids, or unnecessarily fill them. That's just how they were built.

IMHO, there's the possibility of causing issues, if there were to be too great an intervention.

It looks like it will clean up beautifully, with some repointing with lime mortar - a nice feature wall?

A small section of my wall, copied from another thread...

View attachment 347378

Your wall looks stunning! Great work.

Yes, I'm repointing 4 walls (bathroom gable, bathroom exterior, office exterior, and office gable). The office gable wall is the pictures. I think my plan is to remove the ceiling and have a feature wall that goes all the way floor to roof and there'll be stairs up to a loft. Then the 2 exterior walls and bathroom wall will all be done in insulated plasterboard for the best of breathability and insulation.

Thanks for your input and I think you might be right that I could cause issues if I do too much.

P.S. I'm in Aberystwyth, Wales, since I see you're also in Wales. Moved here from Vancouver 18 months ago so I'm still coming to terms with what buildings look like when there's no earthquake risk.

 

[Ivor Windybottom]

It's just how walls were built - face the flat side outwards on each side, don't care about the middle.

I've used a mortar gun before, they're great for this sort of thing. Alternatively just use a trowel with a float or board to repeatedly push fillets in until it pushes back against you.

 

[George_engineer]

Pourable lime grout is available

Lime Green Premixed Pure Lime Grout

Pre mixed natural hydraulic lime and sand. A general purpose lime mortar for building or pointing stone, brick and block: available in different strengths, different sand gradings and colours.

www.womersleys.co.uk

You could make up something similar with quicklime and sand.

While some voids are normal, when built they are backfilled roughly with smaller stones and mortar. If the voids have increased due to rain or plant ingress then grouting can provide good consolidation of the wall. Make sure it is pointed well because it can bleed out during the pour.