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This is why your wall is cracking

When sitting on your patio lost in thought this Saturday, waiting for the braai, you might be staring at your wall and suddenly notice a crack that you could swear was not there before. According to John Graham from HouseCheck, cracks are one of the most common problems found in our homes.

Noticing these cracks on your walls might be an indication of serious structural problems. It is then best to use the services of a professional home inspector and decide from there what your course of action will be. “The home inspection report will examine the possible causes for the cracks and usually recommend a crack repair process,” explains Graham.

Common cracks in your wallscrack-in-home

Foundation cracks

Foundation cracks appear as a result of soil movement and inferior construction. Because your foundation carries the weight of the walls and roof it is very likely that cracks in the foundation will lead to wall cracks too.

Expansive soils

Chances are the soil on which you live is an expansive soil – a soil that contains a high percentage of clay which absorbs a lot of water. This absorption causes the soil to expand by at least ten percent during our rainy season which puts significant pressure on foundations and slabs. During dry months the soil contracts again, leading to a big difference in the pressure exerted on the foundations and slabs of your home.

Here’s how to tell if you are dealing with expansive soils:

Cracked foundations

Heaving and cracking of walls and floor slabs

Jammed windows and doors

Ruptured pipes

Heaving and cracking of paving

Another cause of soil movement is related to soil collapse from sandy soil, or more commonly, eroded foundations that are being undermined by badly managed rain water. For example, downpipes discharging at the base of walls can result in foundation subsidence over time.

Another potential problem is tree roots growing underneath foundations and slabs. The roots can cause surrounding soil to become excessively dry.

Slab cracks

Slab cracks are usually caused either by inferior building materials and construction techniques or due to incorrect placement and compaction of the soil beneath the concrete slab. Weak concrete floor slab will crack, especially if the ground beneath the slab is not suitable and was not compacted correctly before the slab was cast.

Wall cracks

Most wall cracks are not serious; they are probably the result of your foundations settling, mortar shrinking, or a slight roof movement.

There is, however, an exception to this rule of thumb. Some wall cracks may be serious if they are the result of foundation displacement, water penetration or excessive roof movement. This is where the expertise of a professional becomes important. “An experienced and trained home inspector should know the difference,” explains Graham. “The home inspection report should indicate whether a crack is a symptom of structural weakness and which cracks merely indicate the gradual and natural deterioration of structures.”

The most common causes for brick walls cracking are:cracked-brig-wall

Settlement cracks

Settlement occurs as the house “settles” onto its foundation, often leaving “stair step” cracks and diagonal cracks extending upwards from window and door lintels in its wake. Cosmetic repairs such as new paint or crack repair will not permanently fix problems caused by expansive soil.

Thermal cracks

Temperature changes, such as the sun warming and expanding the brick, often leaves the bricks exerting more pressure on one another than previously applied and can result in vertical or stair step cracks.

Water damage cracks

Water penetrating walls from above (especially through cracks on the tops of parapet walls) will cause cracks lower down as the water is drawn downwards through the wall and seeks an exit from the masonry when encountering an impenetrable barrier such as a concrete slab or waterproofing.

Here’s why you need to check your insurance policy again to make sure you know what you’re covered for

Roof movement cracks

Movement of the roof where it rests on the tops of the walls can also cause wall cracks. These cracks are usually slight and can be seen along the line of the ceiling. However the weight and movement of a badly constructed roof can also result in severe structural damage to the walls below.

Roof movement generally results from badly braced rafters and trusses which can exert outward pressure on the tops of load-bearing walls. This is known as truss thrust or truss spread.

Poor anchoring of the roof to the walls can also lead to roof movement – especially in windy areas.

Truss uplift can also occur if the top chords of the truss become damp and expand while the bottom chord remains dry – perhaps because the cross-tie has been covered with ceiling insulation and has not been exposed to the same moist air as the top trusses. Truss uplift can result in cracks along the cornices on inside, non-load-bearing walls.

Plaster cracks

Cracks in plastered walls are common, especially in older houses.

Plaster cracks may result from stresses caused by movement (see discussion above). Crazing cracks of plaster can be caused by incorrect plastering techniques or plaster which has been allowed to dry too fast.

One of the biggest reasons that plaster may crack is caused by changes in ambient moisture levels and different expansion coefficients between mortar plaster, bricks, concrete and steel.

Repairing cracksrepairing-brick-wall

The basics of crack repair are to remove all debris and excavate the crack, down until you reach firm material. After that a suitable, flexible, crack filler or mortar mix can be used to fill the crack.

If it is thought that the crack has resulted from movement which is likely to continue then an attempt can be made to reinforce the wall across the cracked area. This can be done by strengthening the plastered area with a plaster lathe (metal or plastic mesh) or by a technique known as “metal stitching”. Here lengths of metal rod (rebar) are fixed across the crack with epoxy before the crack is filled and the area plastered (perhaps with the use of plaster lathe).

According to Graham there are a variety of proprietary crack repair products available. Armed with the correct information and assistance from professionals you will be able to quickly address any structural problems that may be resulting in cracks.

This feature first appeared on HouseCheck


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  • Michal 5th October 2016

    Very informative article. I always have had a hard time explaining those cracks. Now I know.

    • David A Steynberg 5th October 2016

      Thanks Michal. We found it just as helpful 🙂

  • Tlale Wa Dintlo 6th October 2016

    Thank God . Now my clients know I have been preaching good gospel

    • Furi Sharpen 31st January 2018

      This is a very good article, you definitely want to pay particular attention to the larger cracks. If you suspect any kind of structural damage, I always advise people to contact a structural engineer before getting quotes from foundation repair contractors. The engineer will let you know what needs to be done and that kind of information will save you a lot of money when dealing with contractors.

  • Darwin Painter 30th May 2018

    Thank you for sharing your expertise! Great article