Most cracks in old masonry are stable. Some aren't. Here's how we tell the difference using simple, low-cost monitoring methods anyone can start with.
Cracks unsettle people, understandably. But the first question is never "is there a crack" — it's "is the crack moving, and how fast." A hairline crack that has been stable for thirty years is a very different problem from a fresh crack that has widened by 2mm in the last month.
The simplest monitoring tool is a tell-tale gauge — essentially two overlapping glass or plastic plates fixed across the crack that will themselves crack or shear if the masonry moves further. They cost almost nothing and give a clear yes/no answer over weeks or months.
For more precise readings, we use demountable mechanical (DEMEC) gauges, which measure movement to fractions of a millimetre between fixed reference points. Combined with dated photographs and a simple log, this builds a record that takes the guesswork out of deciding whether intervention is actually needed.
As a rule of thumb: if a crack is moving seasonally (opening in dry months, closing in wet ones) it is often thermal or moisture-related and may not need structural intervention. If it moves in one direction only and keeps growing, that's the point to bring in an engineer for a full assessment.
