When should you worry about cracks in your walls?

Turning a blind eye to cracks in walls may mean you’re missing the warning signs for serious and ongoing structural damage caused by subsidence.

Cracks in walls are common in buildings; though some are nothing to worry about, others can indicate a sinking or damaged foundation (subsidence). If you don’t address problematic cracks in walls, the damage to the foundations can quickly devalue the property.

Cracked Walls in Heritage Buildings

Mainmark has delivered successful results to hundreds of heritage buildings. Our foundation repair methods are a great solution, for many reasons, not least of all raising, re-levelling and re-supporting the building gives it a new lease of life, allowing an historical structure to stand strong into the future.

Buildings that are out of level often develop wall cracks; these can occur internally and externally. As the building is re-levelled these cracks generally close up, leaving only a little patching and painting to deal with. Most importantly, structural damage is resolved, and the long-term future of the building is safe.

When do wall cracks indicate a structural problem?

Larger cracks that display these characteristics may indicate weaknesses in the building’s foundation:

  • One side of the wall is higher than the other
  • Doors and windows no longer close in their frame
  • Cracks are wider than about 5mm (or half a centimetre) or big enough to insert your little finger in them

Problematic wall cracks will typically start at windows, doorways or corners of buildings and are often zig-zag or stepped cracks in brickwork which usually follow the mortar lines. Generally, smaller hairline cracks are not cause for concern. These are usually the result of seasonal expansion and contraction of soils beneath the building over time, and can be easily patched and re-painted.

What causes large cracks in walls?

Large cracks may appear because the property’s foundation has shrunk or lost its strength, causing all or a part of a building to sink, known as subsidence. This usually happens because the moisture in the soil beneath the settled section the building is either too wet or too dry.

Likely causes:

Drought drying out soil, especially soils containing reactive clay

Shrinking clay

Liquefaction caused by earth movement and earthquakes

Washaways from broken pipes


Poorly compacted fill

How to fix large cracks in walls

The best long-term solution for fixing large cracks is to lift, re-level and re-support the building. This level correction process is called underpinning. As the building is re-levelled, the cracks in walls may close or become smaller (ready to plaster or render walls for fine patching and repainting). Windows and doors will also usually begin to work properly again. Traditional underpinning or level correction methods involve excavating or digging up parts of the foundation, pouring in concrete, waiting for it to set and then jacking up the building off the concrete blocks. However, this traditional method can be time consuming (often requiring weeks or months) and messy. It usually means you’ll have to vacate part or all of the building while tradespeople work.

Mainmark’s level correction methods are much friendlier, both to the building and to those that occupy it. Our non-invasive techniques are cost and time efficient.

Various product warranties and Building Code requirements apply (please contact us to see which apply in your region or country).

Key benefits of Mainmark’s level correction methods include:

Non-invasive techniques keep further damage to the building, and the landscaping around it, to an absolute minimum

We don’t tear up floors and excavate ground, so historical integrity remains unaffected

Internal and external wall cracks generally close up, requiring only some cosmetic crack repair treatment (plastering, painting and re-pointing brickwork)

Jammed doors and windows can usually operate properly again

Methods are effective on various foundations, such as, bluestone, brick and sandstone

The methods we use strengthen weak ground, so the building becomes level, crack-free and more stable.