Learn the causes of wall movement and cracking

Cracks in a brick wall may or may not require ­immediate correction. We'll teach you more about what causes these cracks and help you avoid making risky generalizations.

• Before preparing to fill any cracks, it's worth spending some time trying to identify the root cause.
• The trouble usually stems from the footings, which may have ceased to give adequate support to the building. This is particularly common if the weight they have had to bear has increased (like with the addition of another storey). Sometimes the footings themselves may be damaged, or the underlying foundations or earth have subsided or settled.
• Buildings on rock or well-consolidated sandy soils seldom present many problems. Loose sands can be troublesome, but the most difficult soil types on which to build are certain kinds of clay soil and fine-grained alluvial soil. These soils act like a sponge, expanding in wet conditions and shrinking during dry spells, causing cracks to form.
• When going from a wet period to a dry period, the soil under the house usually stays moist and swollen longer than that at the perimeter, which dries out and shrinks more quickly.
• A non-flexible masonry building on such a flexible soil often develops structural cracks. A timber building tends to "ride" the changes better, although the structure may gradually go a little out of square. These problems are made worse if there are vigorous-rooted trees near the house or faulty or leaky drainage and sewer systems.
• The footings of many old houses are inadequate by today's standards. They're often quite shallow and built from stone blocks, rubble or brickwork. None of these materials has tensile strength, so when the building flexes, the footings crack and the walls above follow suit.
• Houses sitting above ground on piers or posts may not have continuous footings. Individual piers may sink, lean, or collapse, and this can also lead to cracking, most notably in timber-framed houses. By contrast, newer homes have deeper, steel-reinforced footings.

• Because the footings of older houses are often inadequate, the addition of a second storey can create severe problems like increased cracking and movement. Always have the footings checked if you intend to build another storey.
• A careful examination under the house with a torch can often determine whether there are any problems with the footings. Call in a structural engineer or a builder if you have any doubts. If the problems turn out to be major (like ­erosion or subsidence) the footings will likely need to be underpinned, an expensive undertaking.

Be sure to inspect your brickwork and footings before starting a construction or repair project. That way you can identify any problems in the materials or terrain. Use this guide to help, and call a professional when in doubt.