No property owner, occupant or neighbor to a cracked building will ever feel safe wether it’s a treat to the building or not. Cracks may affect appearance only, however a crack maybe the first sign of a serious defect which may affect the serviceability or stability of the building. The appearance of cracks will also affect the value of the building, its insurability, the saleability and can be the subject of litigation Occurrence of various crack patterns in the building during construction, after completion when it is subjected to super imposed load or during the service life, is a common phenomenon

Cracking is an inevitable response to the inability of a structure to accommodate the movement or load to which it is subjected. A building component develops cracks whenever stresses in the component exceed its strength. New buildings can be designed and constructed to eliminate many of the causes of cracking and design tolerance for those factors that remain either by introducing joints, or by choosing movement-tolerant materials.

Existing buildings are what they are, and when considering performance an assessment must be made as to the likely cause of movement and the degree of the movement-tolerance inherent in any given structure. The cracks may be predominantly associated with an external cause (as in the case of subsidence) or with the material itself .

Types of Cracks in Buildings
Cracks in buildings could be broadly classified as structural and nonstructural cracks.

1. Structural Cracks: These occur due to incorrect design, faulty construction or overloading
( this is common where property owners carry out modification to buildings or even load building with additional floors without consulting with professionals) and these may endanger the safety of a building. e.g. Extensive cracking of an RCC beam.

2. Non structural Cracks: These are mostly due to internally induced stresses in buildings materials and might not at first endanger safety of a building but may look unsightly, or may create an impression of faulty work or may give a feeling of instability. In some situations due to penetration of moisture through them non structural cracks may spoil the internal finishes thus adding to the cost of maintenance, or corrode the reinforcement, thereby adversely affecting the stability of the Structure in long run. e.g. Vertical crack in a long compound wall due to shrinkage or thermal movement


PRINCIPAL CAUSES OF CRACKS

For prevention or minimise the occurrence of cracks, it is necessary to understand the basic causes and mechanism of cracking, and certain properties of building materials which may lead to dimensional changes of the structural components. The principle causes of cracks are as follows:

1. Lack of or Poor soil investigation (Geotechnic):
The soil is the most important material with the highest varying property in a building construction, same type of soil can change from solid to almost liquid because of change in moisture content. The soil is the natural foundation on which we construct our buildings, any mistake made about soil investigation or geothechnic (read this for more) in relation to our building might lead to a waste of resources or even suicidal. Shear cracks in buildings occurs when there is large differential settlement of foundation due to one of the following cause.

(a) Unequal bearing pressure under different parts of the structure: soil under a building can be of different types and vary in properties and so have varying bearing capacity (ability to carry load) that might not be taken care of in the foundation design and at the time of construction.

(b) Settlement: All buildings settles under its own weight, but settlement has to be even and tolerable, uneven settlement is the number one cause of cracks in buildings especially when the right type of foundation is not used for the building.

(c) Low factor of safety in the design of foundations: Factor of safety is additional precaution taken to take care of oversight in design. If this is not adequate it leads to crack and foundation failure.
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(e) Foundation resting in active zone on expensive soil.

2. Structural design
Lack of or Poor structural design and specifications is another cause of the cracks in buildings. It’s important that the designer considers all the environmental aspects that include soil (Geotechnical) investigations that will enable the designer to come up with a proper design of the foundation.
Normally, buildings are designed for particular uses, this determines the loading assumption of the design engineer for example a building designed as residence will have different structural specifications from the one designed to operate as a worship center, many make mistake of converting buildings to other uses without consulting with professionals.

3. Poor workmanship
The number one culprit of poor workmanship is the property owner, even the educated ones who refuses to engage professionals because of less than ten percent professional fee, they are ready to waste 100% on poor workmanship. Not building to design and specification, Poor mixing of building materials, like cement sand and aggregate will cause cracks in the structural component of a building walls, beams, slabs, column and foundation etc. Normally poor workmanship is as a result of lack of or not hiring professionals, ignorance, carelessness, negligence, lack of proper supervision and many others or a combination of all these.

4. Temperature variations /Moisture change
It’s important to know that most materials tend to expand when subjected to high temperature and contract in cooler temperatures these processes therefore end up causing cracks. Building materials have different rate of expansion and contraction (thermal expansivity) this might cause crack line between different materials if variation in their themal expansion of the materials is wide. Building materials (e.g. Concrete, mortar, burnt clay brick, timber, plywood etc.,) are porous in their structure in the form of inter-molecular space, and they expand on absorbing moisture from atmosphere and shrinks on drying. These movements cause cracks.

5. Growth of vegetation:
Roots of a tree generally spread horizontally on all sides to the extent of height of the tree above the ground at maturity. When trees are located in the vicinity of a wall, they can cause cracks in the building due to expansive action of roots growing under the foundation. Sometimes plants can begin to grow in fissures of walls, because of seeds contained in bird droppings, or carried by wind or other means. If these plants are not removed well in time, these may in course of time develop and cause severe cracking of wall.

When soil under the foundation of a building happens to be shrinkable clay,
cracking in walls and floors of buildings can occur in following ways :
(a) Growing roots of trees absorb water from the soil, which may shrink and cause foundation settlement. The removal of water by shrubs and trees depends on the species, for example a Willow tree can take water from the ground 40 metres away.
(b) In areas where old trees had been cut to make way for building construction roots had de-hydrated the soil. On receiving moisture from some sources, such as rain etc., the soil swells up and causes an upward thrust on a portion of the building resulting in cracks in the building.

6. Lack of (or) poor maintenance
It’s always important to take good care of your building, by doing maintenance works after a lapse of certain periods. This will keep the building intact and also extend their life span.
Water is the number one enemy of a building, even if it is well built, broken drains or water running in the ground from soakaways, ground water or water in service trenches can remove granular soils from below foundation causing subsidence, this is known as washout.
Where minerals or fines are removed from below foundations voids are created causing the material below the foundation to drop and as a consequence of this subsidence occurs, this is known as leaching.

7. Movement due to chemical reaction
Many materials used in the construction of a building are susceptible to chemical reactions Certain chemical reactions in building materials result in appreciable increase in volume of materials, due to which internal stresses are setup which may results in outward thrust and formation of cracks. The material involve in reaction also become weak in strength.

Soluble sulphates which are sometimes present in soil ground water or clay bricks react with tri-calcium aluminate content of cement and hydraulic lime in the presence of moisture and form products which occupies much larger volume than the original constituents. This expensive reaction causes weakening of masonry, concrete and plaster and formation of cracks. For above reaction it is necessary that soluble sulphate, tri-calcium-aluminate and moisture, all the three are present.

The building components, which are, liable to sulphate attack are concrete and masonry in foundation and plinth, and masonry and plaster in super structure. The sulphate attack on these components will result in weakening of these components and in course of time may result in unequal settlement of foundation and cracks in super structure

Conclusion

Most buildings with crack problems are owned by educated owners and professionals, if we ask for the design some have some don’t, if we ask who supervised the construction they say it’s one artisan, if we talk about maintenance they have never even thought about that. We should all know no matter what the repair to cracks it is always better to get it right the first time and avoid cracks.

Jimoh (08085303502)

Thanks for the article.

Nice article.
Are u a structural engineer?

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