Lime only mortar? (i.e. no cement)

[Gibdog]

Hello all,

 

Has anyone else done a timber frame build with brick skin/cladding? I'm trying to make our build as low carbon as possible so would like to use lime mortar - with no cement - but I'm getting push back from the brickie. Has anyone else done this or have any recommendations? 

NHBC have guidelines on bricklaying which all include cement, but is that a rule or recommendation? I know people in the natural building world are using lime only products so it must be possible somehow...!

 

Cheers,

G 

[Mr Punter]

I doubt it would have the strength for modern construction types.  Cavity wall, wall ties, lintels will not work / be properly tested.

[JohnMo]

28 minutes ago, Gibdog said:

but I'm getting push back from the brickie

But what does your structural engineer say - he will have a view based on bond strength and wind loads etc.

[lookseehear]

43 minutes ago, Gibdog said:

Hello all,

 

Has anyone else done a timber frame build with brick skin/cladding? I'm trying to make our build as low carbon as possible so would like to use lime mortar - with no cement - but I'm getting push back from the brickie. Has anyone else done this or have any recommendations? 

NHBC have guidelines on bricklaying which all include cement, but is that a rule or recommendation? I know people in the natural building world are using lime only products so it must be possible somehow...!

 

Cheers,

G 

You also need to remember that there are different types of lime mortar. I'm not sure how familiar you are but broadly you have two types

• Natural Hydraulic Lime (NHL, available in 2, 3.5 and 5 in increasing strength and reducing free lime content)
• Non-hydraulic lime (also technically 'NHL' by name but no-one refers to it as that) also called air-lime or you might see 'lime putty'
  • This can be in the form of quicklime which needs to be slaked, or as hydrated lime ('bagged lime' at the builders merchants) which has already been partially hydrated

I don't actually know how low carbon the different lime mortars are, but my understanding is that they all require burning either pure limestone or some mix of limestone and other stones in a kiln at very high temperatures, and that energy has to come from somewhere, which could be burning coal I guess. I just asked ChatGPT about this and got the below summary.

 

The issue here is that non-hydraulic lime sets very slowly and isn't very strong. It's the best thing for old buildings with solid walls and no DPC, so while there's carbon to be saved, it might not be something you can get sign off from a structural perspective.

[Mike]

2 hours ago, Gibdog said:

Has anyone else done a timber frame build with brick skin/cladding?

No, but you may be able to do it.

 

2 hours ago, Gibdog said:

NHBC have guidelines on bricklaying which all include cement, but is that a rule or recommendation?

The use of lime lies outside the current British Standards, so it would be down to your structural engineer to make an assessment of suitability.

 

However the NHBC Foundation have produced a paper on the subject, which may help - The use of lime-based mortars in new build  (https://www.nhbc.co.uk/binaries/content/assets/nhbc/foundation/the-use-of-lime-based-mortars-in-new-build.pdf) which does say that "The data available indicates that single skin brickwork or blockwork masonry constructed with lime-based mortars quickly develops sufficient resistance to vertical loads, but that it has less resistance to lateral loads at an early age and so consideration needs to be given to this at the design stage."

 

Edited April 7 by Mike

[maxe307]

The pushback from the bricklayer is because lime mortar takes longer to set so building a wall takes more time but you are the client so if thats what you want then its more than possible. Its also great because should your project get knocked down in the future they can scrape the lime mortar off the bricks and reuse them. There are plenty of HLM projects throughout the UK. 

[Rishard]

Lime is another world. My guesses are, if your Bricky isn’t familiar with it then you would need to find another. I’ve no doubt he could work with lime but it does require a bit of guidance. It would be a bit of a learning curve, if you’re happy for him to learn on your job, that would be up to you. 
 

What you really want is a hot mixed lime mortar, gauged appropriately with a local pozzalan to fit in with the local vernacular. I’ve rebuilt a barn with hot lime, some solid walls and some cavity wall with insulation. In this case it was stone with a 150mm bed with wall ties. We laid stones roughly 7-9” inches height up to 30” long. Compressive strength is very different with hot lime mortar. It firms up very quick unlike putty mixed lime which means you can lay as quick as you could with sand and cement. 
 

 

[goodbyegti]

We used lime NHL 3 (otterbein), 1 part to 2 parts yellow sand and 1 part grit. It still looks great after a couple of years. It was hard getting a regular bricky to mix it properly. Luckily we found some good masons. You also have to beat it back at just the right time to pack it into the joint. I'd do it again!

 

[Rishard]

Looks great! The stone here is very soft sand stone and would degrade even with an NHL. 
 

What is the brick you’re using? 

Edited April 7 by Rishard

[goodbyegti]

Thanks! It's 125mm cropped Purbeck limestone and a bit of blue lias. Up against some Surecav except the end which is solid.

 

[Rishard]

Is that a little leaded oak lintel? Lovely stuff 

[SteamyTea]

On 07/04/2025 at 08:31, Gibdog said:

I'm trying to make our build as low carbon as possible so would like to use lime mortar - with no cement

That is not where the embodied CO₂ savings are to be made, there is just not enough of it in a building.  The delivery to site will probably produce more CO₂.

 

There are a number of ways to reduce CO₂, daily energy usage is probably the most important.