12/10/2026
Have you heard of lime torching?
It’s something you’ll often come across in the roof spaces of older properties.
Before roofing felt became widely used, lime mortar was often applied to the underside of roof slates to help prevent wind-driven rain, snow and draughts from entering through gaps between the slates.
This traditional technique is known as torching.
Interestingly, animal hair was also commonly mixed into the lime mortar, which helped strengthen it and reduce cracking as it dried.
If you look closely at the third photograph, you can see animal hair within a piece of the original mortar.
Over time, the torching can become loose, crack and eventually fall away, as can be seen here.
Whilst this is quite common in older properties, deteriorated torching doesn’t necessarily mean the roof needs replacing.
The condition of the slates, their fixings and the overall roof covering is much more important when assessing the roof’s condition and whether repairs are necessary.
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