15/09/2026
š Thinking about buying a house with Black Ash Mortar (Lime Clinker)? Read this first! ā ļøIf you own an older home, you might have heard of black ash mortar (often containing lime and clinker). While it was commonly used in certain regions during the 19th and early 20th centuries, it comes with two massive warnings for homeowners:
1ļøā£ It is highly corrosive to metal. Because black ash mortar contains high levels of sulfur, it reacts heavily when moisture is present. If you have wall ties, structural steel, or metal pipes embedded in this mortar, it can rapidly corrode and expand. This often leads to "wall tie failure," causing walls to bulge, crack, or even become structurally unstable.
2ļøā£ It triggers false "damp meter" readings. Trying to diagnose a damp issue with a standard pin-type moisture meter? Be careful! Black ash mortar is highly conductive due to its carbon and salt content. A damp meter works by measuring electrical resistanceāmeaning it will often give sky-high, alarming readings even if the wall is actually dry.
The Takeaway: Always get a qualified independent surveyor to carry out a proper inspection! !