Does this old stone wall need lime motar?

[Mark and Jen]

My house is an old mill and the (now dry) race runs around the house still as a sunken trench. It is lined with an old stone wall (I have these all over the place - the house, the barn, garden walls, etc) This one has the top line of stones loose and I need to re-fix them. In the past it has been patched with concrete (and a tar drive laid alongside it) - I have no real need to do anything beyond "make this safe" - i'm not fussed how it looks within reason - so can I just use regular mortar to re-fit the stones...or cement? Or should I use lime mortar? I understand on a building wall lime is needed - and when I do my barn it will be done that way (already had a lime expert on site to advise) But for this sort of "outdoor" wall - that has been patched over the years in concrete....does it really matter? And yes, it's getting cleaned out first! Lots of jobs here!!!

 

[aockenden]

It’s not super important in that situation. The only risk with using cement on something like that is if it’s too hard and the stones are too soft, the stone could potentially crack / spall / crumble with freeze and thaw cycles during winter. If the stone is hard, it likely would be fine to use cement.

 

[Mark and Jen]

And would that be cement or mortar in that application? I'm a bit new to this!

 

[aockenden]

And would that be cement or mortar in that application? I'm a bit new to this!

A mortar is a composite material consisting of 3 primary ingredients: a binder, an aggregate (sand, gravel, etc), and water.

Cement is a type of binder. Lime is another type of binder. Clay is another binder. There are other binders as well.

Therefore, you can make a cement-based mortar (cement + sand + water), you can make a lime-based mortar (lime + sand + water), and you can make a clay-based mortar (clay + sand + water). All of them are mortars, but only one of them contains cement.

Does that make sense?

 

[a twig]

And would that be cement or mortar in that application? I'm a bit new to this!

I’d recommend used NHL3.5 in a ratio of 1 NHL : 1 sharp sand : 2 builders sand.

NHL3.5 is available from most Travis Perkins

 

[Stevers]

That could do with being topped with a row of chunky capping stones to form a kerb - for function, looks and and safety.

 

[Mark and Jen]

I’d recommend used NHL3.5 in a ratio of 1 NHL : 1 sharp sand : 2 builders sand.

NHL3.5 is available from most Travis Perkins

That will do for me! I'm off shopping!

Daft question.....I know from chat with lime expert that a lime/water mix will stay useable for a long time. But with this sort of mix for lime mortar, if I don't finish my job I assume I can't expect the mix to stay workable? (or can I seal any unused in an airtight container and get back to it the next day?)

 

[Mark and Jen]

A mortar is a composite material consisting of 3 primary ingredients: a binder, an aggregate (sand, gravel, etc), and water.

Cement is a type of binder. Lime is another type of binder. Clay is another binder. There are other binders as well.

Therefore, you can make a cement-based mortar (cement + sand + water), you can make a lime-based mortar (lime + sand + water), and you can make a clay-based mortar (clay + sand + water). All of them are mortars, but only one of them contains cement.

Does that make sense?

Makes perfect sense - so what does adding the agregrate do to the finished mix? In ortherwords.....how is a cement mortar different in function and use to a straight cement/water mix?

 

[Mark and Jen]

That could do with being topped with a row of chunky capping stones to form a kerb - for function, looks and and safety.

You want to see the edge of our patio that is a 6ft drop into the river 12ft from the front door! Safety is absent around here )).

But....do you just mean set some bigger raised stones in the mortar to give it a proper edge to bump into before the car tyre goes over it?

 

[aockenden]

Daft question.....I know from chat with lime expert that a lime/water mix will stay useable for a long time. But with this sort of mix for lime mortar, if I don't finish my job I assume I can't expect the mix to stay workable? (or can I seal any unused in an airtight container and get back to it the next day?)

If you are using an NHL (naturally hydraulic lime) as twig recommended, it does NOT stay useable once mixed with water for any more than maybe a day or so (whether or not it’s kept underwater, in an airtight container, etc). Only non-hydraulic limes remain useable for long periods when kept airtight or underwater.

The advantage of the NHL in your case is that it’s simple to use and widely available but no it won’t keep. Use it up within a day or it’s junk.

 

[aockenden]

Makes perfect sense - so what does adding the agregrate do to the finished mix? In ortherwords.....how is a cement mortar different in function and use to a straight cement/water mix?

Depending on the aggregate it can significantly improve the compressive strength of the mortar. It’s also a much cheaper bulk filler vs lime or cement, both of which are energy intensive to manufacture. Locally available sand is anywhere from 1/5th to 1/20th the price of lime or cement by volume. Aggregate also reduces the shrinkage experienced as the mortar dries.

 

[Flyfisher]

I've always thought of mortar being binder+sand, ie cement+sand or lime+sand and adding aggregate to the mix would make concrete.
Thus, cement+sand+gravel* = concrete and lime+sand+gravel* = limecrete, though I'm not sure if this is technically correct.

*gravel is just one example of an aggregate.

 

[stuart45]

Sand is an aggregate, as is gravel. The difference between the 2 is the size of the particles.

 

[Mark and Jen]

If you are using an NHL (naturally hydraulic lime) as twig recommended, it does NOT stay useable once mixed with water for any more than maybe a day or so (whether or not it’s kept underwater, in an airtight container, etc). Only non-hydraulic limes remain useable for long periods when kept airtight or underwater.

The advantage of the NHL in your case is that it’s simple to use and widely available but no it won’t keep. Use it up within a day or it’s junk.

OK - so the NHL i use to mix with sand for this project is not the same HL that my lime guy is coming back with next week to teach me how to fix my barn the "right way"?

 

[aockenden]

OK - so the NHL i use to mix with sand for this project is not the same HL that my lime guy is coming back with next week to teach me how to fix my barn the "right way"?

Only he can answer that.

 

[noj]

HL = Hydrated Lime
NHL = Naturally Hydraulic Lime

NL (AKA air lime, fat lime, lime putty) only sets/cures by absorbing CO2 from the air, can be stored underwater almost indefinitely, makes the most 'breathable' and softest mortar/render/plaster.

NHL cures in the presence of water (even underwater), comes in three strengths (2, 3.5 & 5) and behaves more like cement.

 

[Cubist]

Regarding the mortars choice, I would take my cue from what was used in the walls original construction. Certainly Lime based and its greater permeability will aid drainage from beneath that tarmac covered section. A cement based mortar would be far less effective and could increase the risk of differential movement damage.

 

[noj]

An addition to my earlier post - once you've got your head round hydrated and hydraulic lime - is what the lime + aggregate + water mix is called!

1. Mortar: if you're building masonry work or pointing it
2. Render: if you're spreading a layer on a substrate externally
3. Plaster: if you're spreading a layer on a substrate internally
4. Limecrete: if you're using it in isolation (such as creating a floor slab)

Theoretically all the same thing, although in practice you'd probably use different aggregates...