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- 1 to 5mm is minor. Again, normal decoration is called for.
- 5 to 15mm is a moderate crack. It needs normal repairs; minor masonry replacement.
to 25mm is a severe crack requiring extensive repair work or even the replacement of a section of the wall.
- Over 25mm is a very severe
crack which will need major repair work and/or partial rebuilding.
There are various types of cracks.
Settlement cracks happen
as the house “settles” on to its foundation. They are often in the form of “stair step” cracks and diagonal cracks extending upwards
from window and door lintels. Cosmetic repairs such as new paint or crack repair will not permanently fix problems caused by expansive
- Thermal cracks are caused by temperature changes, the sun warming and expanding the brick. This means the bricks exert 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.
- Roof movement cracks. Movement of the roof structure, where it rests on the wall plates along the
tops of the walls, can also cause wall cracks. These are usually slight and can be seen along the line of the ceiling and cornices.
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.
cracks are common, especially in older houses. One of the biggest causes of plaster crack is changes in ambient moisture levels and
different expansion coefficients between mortar plaster, bricks, concrete and steel.
First, remove all debris and
excavate the crack down to firm material. Use a flexible crack filler or mortar mix to fill the crack. If you think the crack has
resulted from movement which is likely to continue, then you could try 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.
Cracking around windows can cause leaking and water coming into the walls, creating cracks in exterior walls which
then penetrate internally.
The main cause of leaking around windows is that the windows have not been installed properly.
sides and bottom of the window should have a length of damp proof course fitted and this should then be built into the surrounding
brickwork and cills. Trying to rectify this after the event is no easy task and will often cause more problems.
As long as the
cracks are not being caused by movement, then the best method is to seal the cracks with a flexible filler around the window frames.
It is a waste of time and money to do any internal repairs or remedial work until the external walls have been properly sealed and
the internal walls have dried out completely. This can take anywhere up to six months depending on the amount of water in the walls.
an article in the Cape Argus
I can inspect and identify problems with the cracks in your home and roof and report
on the condition of the structure and whether the cracks might be active or non-active and danger to you and your family.
Plaster Repairs >
Most houses in South Africa will sooner or later develop wall cracks. Few are serious, and can be ascribed to slight settlement of
the foundations, mortar shrinkage, or slight roof movement. However, some cracks can be potentially serious and are the result of
significant foundation displacement, water penetration, or excessive roof movement.
The most common reasons for cracking of brick
walls are settlement, thermal expansion, moisture penetration and roof movement.
The National Home Builders Registration Council classifies
cracks as follows:
Less than 1mm in crack width is very slight. Normal decoration will sort it out.
What to do about cracked walls
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