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How should I repair a crack that has appeared in the side wall of my house?

Cracks in homes or apartments or any structure aren’t necessarily an indication of imminent disaster. They’re often a signs of soil movement.

Soil movement is caused by changes in its moisture content and is more evident in inland clays than in coastal sands. Whilst excessive moisture (caused by an undetected leaking pipe, for example) causes soil to swell, drying causes it to shrink and our continuing drought is the cause of many cracks.

Aided by increasingly thirsty trees, it’s slowly drying out our soil and causing movement beneath our homes, particularly affecting older building stock. Thankfully, these days we’re better at predicting soil behaviour than we were in the “good old days” – we design new homes for local conditions using techniques such as pier and beam footings or movement control joints.

According to accepted industry standards, cracks less than 5mm wide aren’t necessarily cause for concern, however larger cracks can mean some reconstruction work. If the crack is a result of foundation shrinkage it may well close up when the soil becomes moist again. This will probably occur naturally during the wetter season, however you can hurry it along by re-hydrating the area using a drip-watering system (be sure to check your local water restriction first!). If the area around the base of the wall is paved, consider replacing the paving with porous material or planting – this will ensure that water permeates the soil rather than running off.

Above all,  don’t fill the crack with mortar – use a flexible, exterior grade sealant. If and when the foundation soil does swell back into its natural state, the brickwork will want to move back into place and an inflexible filler will simply induce a crack elsewhere. Alternatively just measure it and keep an eye on it to see if it’s getting better or worse. If it doesn’t close up or if it gets bigger or just for your own peace of mind, call AGA for our professional, independent building advice.