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

[Oxbow16]

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

 

 

 

 

 

Edited September 18, 2023 by Oxbow16

[Oxbow16]

More photos

 

 

 

 

 

 

[Iceverge]

I'd say you're on the correct path with a lime mix. 

 

I'd be tempted to put in a bit of cement for a small bit of strength. It'll be a compromise between not trapping moisture in the wall and putting something in that isn't too weak. 

[Oxbow16]

Would NHL 5 still be too weak do you think?  Would you use that strength and add cement as well?  

 

Many thanks

[jayc89]

NHL 3.5 mixed 3:1 will be fine. Save NHL5 for under water and exposed conditions (like chimney stacks on top of the Dales). 

[Oxbow16]

17 hours ago, jayc89 said:

NHL 3.5 mixed 3:1 will be fine. Save NHL5 for under water and exposed conditions (like chimney stacks on top of the Dales). 

 

We do live in a wet area generally.  and since the "trench" has been exposed, water has pooled in it after rainfall and takes a while to go.  I guess the ground is very compacted there which prevents the water draining away.  So due to the amount of rain we see and the fact that the ground is so often wet, I had wondered if NHL5 would be better suited?  Perhaps for the extra strength too seeing as it is beneath a two storey wall?  On the other hand, I appreciate it is also a balance of getting the most breathable option. 

 

With all that in mind, would you still say 3.5 is best? 

 

Funnily enough, I have been reading that in some brands there's little difference between 2, 3.5 and 5.  And that across brands there's so much variance that a 2 by one company is close to/the same as a 5 from another.  Which I guess make a mockery of it all if true!! 

 

Many thanks for your help      

[Nick Thomas]

2 hours ago, Oxbow16 said:

We do live in a wet area generally.  and since the "trench" has been exposed, water has pooled in it after rainfall and takes a while to go.  I guess the ground is very compacted there which prevents the water draining away.  So due to the amount of rain we see and the fact that the ground is so often wet, I had wondered if NHL5 would be better suited?  Perhaps for the extra strength too seeing as it is beneath a two storey wall?  On the other hand, I appreciate it is also a balance of getting the most breathable option. 

 

 

If you use NHL5, it'll be relatively impermeable, so the water you currently see in the voids will be more likely to stay higher up. Is that desirable in your case?  Same if you added a bit of cement to it - the water will be slower to move through (if at all), so it'll end up going elsewhere. Into the house?

[jfb]

I’d go with 3.5

 

make sure it’s a good sharp sand nothing too fine

[Mr Punter]

Sharp gritty aggregate and well rammed in or even MOT type 1.

[jayc89]

3 hours ago, Oxbow16 said:

 

We do live in a wet area generally.  and since the "trench" has been exposed, water has pooled in it after rainfall and takes a while to go.  I guess the ground is very compacted there which prevents the water draining away.  So due to the amount of rain we see and the fact that the ground is so often wet, I had wondered if NHL5 would be better suited?  Perhaps for the extra strength too seeing as it is beneath a two storey wall?  On the other hand, I appreciate it is also a balance of getting the most breathable option. 

 

With all that in mind, would you still say 3.5 is best? 

 

Funnily enough, I have been reading that in some brands there's little difference between 2, 3.5 and 5.  And that across brands there's so much variance that a 2 by one company is close to/the same as a 5 from another.  Which I guess make a mockery of it all if true!! 

 

Many thanks for your help      

 

There are very few use cases for NHL5 now, you may as well use cement. It doesn't want to be anywhere near your stonework. You'd be better off going weaker and repointing often, then going harder and watching the stone start to spall. 

[jayc89]

Good example of brickwork spalling, spot where the cement pointing was - 

 

[Oxbow16]

21 hours ago, jayc89 said:

 

There are very few use cases for NHL5 now, you may as well use cement. It doesn't want to be anywhere near your stonework. You'd be better off going weaker and repointing often, then going harder and watching the stone start to spall. 

 

That's fair enough and makes sense.  In a lot of ways I'd prefer to use 3.5, so all the better if that's the most appropriate.  

 

Regarding repointing though, once I've finished I'll leave the "trench" as it is so that the mortar can set.  But at some point (not sure how long to leave it?) I'll back fill the trench and re-instate normal ground levels, after which the work won't be visible or accessible and so I'm not sure repointing be an option in the future?  

 

Cheers

[Oxbow16]

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

[markc]

2 hours ago, Oxbow16 said:

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

Brush out any loose soil and then ram the semi dry mortar in.