Lime mortar is having a moment again. Homeowners, conservation officers and heritage enthusiasts are increasingly demanding it on old buildings – often insisting it’s “the only correct way”. But on-site, most modern builders actively avoid it.
So what’s the real story?
This piece explores lime in all its forms – what it is, how it behaves, why it fell out of favour, and why there’s now a push to bring it back.
It also tackles one of the biggest myths in building today: that plasticised cement mortar is a valid substitute for lime.
You’ll see the practical reality of working with lime, the reasons bricklayers dislike it, and where it genuinely earns its place in historic construction.
From old lime kilns to modern site practice, this goes beyond romantic notions and looks at how walls actually perform over decades.
_______________________
Key Takeaways
• Lime is not one material – there are several types with very different behaviours
• Non-hydraulic lime (lime putty / hydrated lime) sets by carbonation and remains highly breathable
• Hydraulic lime sets with water first, then continues to carbonate over time
• Hot-mixed lime is the traditional method, now mainly used on specialist conservation work
• Portland cement replaced lime because it is faster, stronger and more predictable
• Plasticiser only mimics the feel of lime, not the long-term performance
• True lime mortars allow moisture to escape, reducing trapped damp in old walls
• Lime mortars can self-heal small cracks through autogenous healing
• Many builders dislike lime due to slow curing, added risk and longer programmes
• A common compromise is the 6:1:1 mix (sand : lime : cement) used for speed and familiarity
• Hydraulic lime can be too strong for soft historic bricks if poorly specified
• Poor choice of mortar can accelerate brick and stone decay
_______________________
Betchworth Quarry and Lime Kilns
https://what3words.com/cycles.bottom.crate
Picture Credits
Hugh Craddock / Betchworth quarry and limekiln
_______________________
#LimeMortar
#BuildingRestoration
#HistoricBuildings
#Repointing
#TraditionalBuilding
#Brickwork
#HeritageSkills
#ConstructionTruth
#OldHouses
#BreathableWalls
