Hairline cracks are symptoms of possible problems. Proper diagnosis and treatment will ensure safety, feelsASWATH M.U.
In any industry, whether it is construction, IT or electronics, the fundamental knowledge of a candidate is tested before he is given a job. But in this age of speed, many a times we fail to understand the importance of basic procedures. However advanced we are, well-established rules should not be dismissed.
For good construction practices, the construction documents contain the specifications and instructions for quality execution of works. Unfortunately, field engineers and builders fail to understand the significance of these instructions and they fail to implement them completely, leading to problems. One such common problem is cracks in buildings. All types of cracks including hairline cracks can be avoided by adopting good construction practices.
Cracks can be observed in new and old buildings and also buildings subjected to forces such as earthquakes. Cracks may be horizontal, vertical, step-like, straight, uniform, diagonal, inclined, web-like map pattern or random in nature.
Cracks are generally seen on unplastered or plastered/rendered surfaces, just below the window/ventilator sills, corners of openings, near lintels, on beams (centre and near supports), near joints, corners of walls, beam-wall junction, column-wall junction, beam-column joints, near cross walls, on long walls, on dwarf-short walls like parapet and compound wall, next to foundation plinth, junctions of in-filled walls in framed structures, just above the electrical and other pipelines on wall and floor surfaces, junctions of balcony slabs and walls and on the surface of terraces. Crack width is an indication of its severity.
Cracks may be thin/negligible (hairline cracks) less than 1mm and can be covered by redecoration or plastering; medium/slight severity, 1 to 2 mm in width, can covered by filling the open voids and carrying out redecoration and repainting the affected area; wide/moderate severity, 5 to 15 mm in width, require proper investigation by a professional engineer and remedial work shall be done accordingly; wide /severe, up to 25 mm, indicate structural damage; very wide and very severe, above 25 mm, indicates severe structural damage.
The hairline cracks are non-structural in nature but the other structural cracks should be diagnosed, investigated by an expert and an appropriate remedial measure can be adopted. The structural cracks are characterised as flexural (tensile) cracks, shear cracks and compressive cracks.
Causes of cracks
The reasons for cracking are many. Malcolm Hollis, professor of building pathology at the University of Reading, who is a specialist in the identification and recording of defects in building construction, particularly the investigation and interpretation of cracking in buildings, leak tracing and remedy, had stated: “Surveying buildings is an art, verifying the cause of failure is a science”.
It is therefore very important to accurately assess and identify the cause of cracking before taking up repair work.
Prevention of cracks is very important like any other disease as the treatment/repair is costly and a very tedious process and cannot be done to complete satisfaction.
Some of the common causes of cracking are: foundation movement and settlement of soil (takes place on loose, soft and highly compressible soils); incompatibility of building materials; chemical reaction of materials; thermal expansions (tensile and compressive stresses develop within the building elements due to temperature changes, cracks can occur if the building element is restrained and lacks sufficient construction joints to accommodate the movement); changes in moisture content (clay bricks initially expand and concrete blocks experience shrinkage following curing; if the materials are used together monolithically, stresses can develop with resulting cracks); structural instability (the structural failure of the building can cause cracks as well as stresses on individual elements, causing cracking).
Elastic deformation, creep, shrinkage, delayed curing, bleeding, formwork movement, and excessive vibration during concreting, quality of materials, corrosion of reinforcement, vegetation growth near the buildings and structural design deficiencies are some other causes.
The basic common construction materials we use include cement, sand, stone, brick, mortar, concrete and concrete products.
The understanding of the physical, chemical and structural behaviour of these materials and their effective use solves most of the common problems. Cracks can be avoided by: adopting proper methods of placing & finishing mortars and concrete, sufficient curing; avoiding excess of dust and silt in sand; providing construction joints and expansion joints; proper compaction of soil below the foundation; avoiding vegetation growth especially close to the foundations; and safe structural design.
By selecting a contractor based on his knowledge and not just by his blind experience of the number of works he has carried out and adopting good construction practices, we can avoid cracks in buildings.[The author is Professor at Bangalore Institute of Technology and Secretary General-ACCE (I)]