Cracks in a building are rarely random. They are the visible end of a story that usually begins with the materials chosen, the way they were proportioned and placed, the soil beneath, or the climate around the structure. Cracks can arise from chemical reactions within construction materials, changes in temperature and climate, foundation movement and settlement, and environmental stresses such as nearby traffic, railways or earthquakes. Faulty design, poor-quality materials, an incorrect method of construction, weathering and ordinary wear and tear can all leave their mark on walls, floors and ceilings.
Understanding why a crack has formed is the first step towards preventing it. This article sets out fourteen of the most common causes of cracking in buildings, together with practical measures to prevent each one. Many of these themes connect closely with sound project oversight — for individual homes, our guide on three tips for constructing an independent home is a useful companion read.
1. Elastic Deformation
When walls are unevenly loaded, the variation in stresses across different parts of a wall causes cracks to form. Where two materials with widely differing, elastic properties are built together under load, the differing shear stresses create cracks at the junction between them. Dead and live loads both cause elastic deformation in the structural components of a building.
2. Thermal Movement
Thermal movement is one of the most potent causes of cracking in buildings. All materials expand on heating and contract on cooling. The thermal movement in a component depends on factors such as temperature variation, dimensions, the coefficient of thermal expansion and other physical properties of the material. The coefficient of thermal expansion of brickwork is fifty per cent greater in the vertical direction than in the horizontal direction, because there is no restraint to movement vertically.
Thermal variation in internal walls and intermediate floors is modest and does not usually cause cracking. It is mainly the external walls — especially thin walls exposed to direct solar radiation — and the roof that undergo substantial thermal variation and are therefore liable to crack.
3. Chemical Reaction
Chemical reactions within building materials can increase their volume and internal stress, which in turn causes cracks and weakens the components of the structure. Common instances include:
- Sulphate attack on cement products
- Carbonation in cement-based materials
- Corrosion of reinforcement in concrete
- Alkali–aggregate reaction
4. Shrinkage
Most building materials expand as they absorb moisture from the atmosphere and shrink as they dry. Cement-based materials shrink as the moisture used in their construction dries out. The principal factors causing shrinkage in cement concrete and cement mortar, and their prevention, are set out below.
a. Excessive water: Excess water in concrete causes it to shrink. Well-compacted concrete with a lower water content shows better shrinkage resistance.
b. Quantity of cement: As a rule, the richer the mix, the greater the drying shrinkage.
c. Un-graded aggregate: Aggregate can also cause shrinkage. Un-graded, fine aggregate demands more water and can therefore cause greater shrinkage.
d. Curing: After concrete is laid, the cement hardens, moisture reduces and shrinkage occurs — which in turn causes cracks.
e. Excessive fine material: Fine material has a large surface area and requires more water. Excessive fines — silt, clay and dust in the aggregate — create more shrinkage.
5. Foundation Movement and Settlement of Soil
Shear cracks occur when there is large differential settlement of the foundation, arising from any of the following causes:
- Unequal bearing pressure under different parts of the structure
- Bearing pressure exceeding the safe bearing strength of the soil
- A low factor of safety in the foundation design
- Local variation in the nature of the supporting soil
6. Earthquake
Cracks may occur when there is a sudden shift in the lower layers of the earth. Voids in the ground can collapse abruptly and refill with soil from above. Many geological events trigger such earth movements, resulting in cracking.
7. Vegetation
The roots of trees growing close to a wall can cause cracks as they spread beneath the foundation. In clay soils, cracking also occurs because of the moisture the roots draw out.
8. Permeability of Concrete
Because deterioration in concrete begins with the penetration of aggressive agents, low permeability is the key to durability. Concrete permeability is governed by the water–cement ratio, the degree of hydration and curing, air voids from deficient compaction, micro-cracks from loading, and cyclic exposure to thermal variation — the first three of which also relate to strength. Given good-quality materials, satisfactory proportioning and good construction practice, the permeability of the concrete is a direct function of the porosity and the interconnection of pores within the cement paste.
9. Corrosion of Reinforcement
Properly designed and constructed concrete is initially water-tight, and the reinforcement within it is protected by a physical barrier of low-permeability, high-density cover. Concrete also offers steel chemical protection: steel will not corrode while the surrounding concrete remains impervious and alkaline, with a high pH value.
Despite this, there are many cases where corrosion of reinforcement has damaged concrete structures within a few years of construction. Corrosion caused by carbonation can largely be arrested through sound repairs, but chloride-induced corrosion is far more difficult to treat and frequently recurs soon after extensive repair. Repairing corrosion involves several careful steps — removing carbonated concrete, cleaning the reinforcement, applying a protective coat, making good the lost steel section, applying a bond coat and replacing the cover. Where chlorides are present in the hardened concrete, protecting the steel becomes extremely difficult.
As corrosion products form, the increase in volume creates high radial bursting stresses around the bars, producing local radial cracks and longitudinal cracks parallel to the bar. The resulting loss of mass, stiffness and bond makes repair inevitable, as considerable strength is lost.
10. Poor Construction Practices
The construction industry has, in general, fallen prey to non-technical people, many of whom have little or no knowledge of correct construction practice. There is a widespread lack of good practice arising from ignorance, carelessness, greed or negligence — or, worse still, a combination of all of these.
A building under construction is in its formative period, much like a child in the womb: just as the mother must stay well nourished and healthy for the child to form well, the construction agency and the owner must ensure good material selection and good practice for a healthy building. Every step, right through to completion, must be properly supervised and controlled without cutting corners. The main causes of poor practice and inadequate quality include:
- Improper selection of materials
- Selection of poor-quality, cheap materials
- Inadequate and improper proportioning of the constituents of concrete, mortar and so on
- Inadequate control over batching, mixing, transporting, placing, finishing and curing
- Inadequate quality control and supervision, causing large voids (honeycombs) and cracks that lead to leakage and faster deterioration
- Improper construction joints between successive concrete pours, or between framework and masonry
- Addition of excess water to concrete and mortar mixes
- Poor-quality plumbing and sanitation materials and practices
Disciplined supervision is precisely where professional oversight earns its place — see our note on the importance of safety protocols in construction project management, and on using value engineering to balance cost and quality without compromising durability.
11. Poor Structural Design
Very often a building loses its durability on the drawing board itself, or while the specifications for concrete and related parameters are being prepared. The designer must first consider the environmental conditions around the site, and it is equally important to carry out geotechnical (soil) investigations to determine the type of foundation, the materials to be used and the grade of concrete — having regard to the chemicals present in the ground water and subsoil.
It is also critical that the designer and architect know whether the proposed construction agency has the skills and experience to execute their design. Complicated designs with dense reinforcement in slender sections often result in poor-quality construction; combined with an inadequately skilled contractor, this ultimately leads to deterioration.
Closely spaced bars and slender concrete shapes encourage segregation. When concrete is placed carelessly into the formwork, it strikes the reinforcement and segregates: fine material sticks to the steel and is lost from the mix while the coarse material falls below, producing large voids (honeycombs). Slender members such as canopies (chajjas), fins and parapets are often the first targets of an aggressive environment, owing to dense reinforcement, poor detailing and thin cover. The structural consultant must provide adequate reinforcement so that such members do not develop large cracks under load.
Prevention — construction practice and structural design
- Proper specification for concrete materials and concrete
- Proper specifications to address environmental and subsoil conditions
- A constructible and adequate structural design
- Proper quality and thickness of concrete cover around the reinforcement
- Planning a proper reinforcement layout, detailed for slender members so concrete can be placed without segregation
- Selection of a suitable agency to construct the design
Architects and engineers are the parents of the buildings they design, and their contribution to a building’s health and life is significant. Once the plans, structural design and specifications are ready, it falls to the construction agency to turn the blueprint into reality. Special care in design and detailing must be supplemented by continuous inspection through every phase of construction.
12. Poor Maintenance
Every structure needs maintenance after a certain period from completion. Some require an early look into their deterioration, while others sustain themselves for many years — depending on the quality of design and construction.
Regular external painting helps, to some extent, to protect a building against moisture and chemical attack. Waterproofing and protective coatings on reinforcement or concrete are a second line of defence, and their success depends greatly on the quality of the concrete itself.
Leakages should be attended to as early as possible, before corrosion of the embedded steel begins and the concrete spalls. Spalled concrete loses strength and stiffness and accelerates corrosion, because the rusted bars are then fully exposed to the environment. It is essential not only to repair the deteriorated concrete but, equally, to keep moisture and aggressive chemicals out and so prevent further deterioration.
13. Indiscriminate Additions and Alterations
There have been building collapses in our country caused by indiscriminate additions and alterations carried out by interior decorators at the request of their clients.
The first target of modification is usually the balcony: to gain floor area, balconies are commonly enclosed and repurposed. Balconies and canopies are generally cantilever RCC slabs; under the additional loading they deflect and crack. Because the reinforcement in these slabs has thin cover and is exposed to an aggressive external environment, the steel corrodes and repairs become necessary.
Loft tanks are often installed in toilets or kitchens — humid areas of the building. The structure is then not only overloaded but also more prone to reinforcement corrosion, so it deteriorates and, if left unrepaired, part of the building can even collapse.
14. Creep
Concrete subjected to sustained loading exhibits a gradual, time-dependent deformation known as creep. Creep increases with higher water and cement content, a higher water–cement ratio and higher temperature; it decreases with greater humidity in the surrounding atmosphere and with the age of the material at the time of loading. The use of admixtures and pozzolanas increases creep, and the amount of creep in steel increases with a rise in temperature.
A final word
Most cracking is preventable. It comes down to sound design, the right materials in the right proportions, disciplined construction and timely maintenance — each supported by competent, independent supervision. If you are planning, building or repairing a structure, our team would be glad to help you get it right the first time. Get in touch with ANPCPMC.
Frequently asked questions
Are all cracks in a building a sign of structural damage?
No. Many cracks are cosmetic — for example, fine hairline cracks in plaster caused by drying shrinkage or ordinary thermal movement. Cracks become a concern when they are wide, keep growing over time, run diagonally across load-bearing walls, or appear together with sagging floors or doors that stick. When in doubt, have the crack assessed by a qualified structural engineer before deciding on repairs.
What is the most common cause of cracks in buildings?
There is rarely a single cause. In practice, thermal movement, drying shrinkage of cement-based materials and differential settlement of the foundation are among the most frequent. Poor construction practice — excess water in the mix, inadequate curing and weak supervision — tends to make all of these worse.
How can I prevent cracks when constructing a new house?
Prevention starts on the drawing board: a sound structural design, a proper foundation based on soil investigation, good-quality materials, a correct water–cement ratio and disciplined curing for at least seven to ten days. Movement, expansion and control joints should be planned where needed, and every stage should be properly supervised. Engaging an experienced project management consultant helps ensure these steps are actually followed on site.
