Cracks in Buildings and Corrective Measures

Cracks in buildings are of common occurrence. Not all cracks should make a building owner panic,but not all cracks should be ignored. A component of a building develops cracks whenever stresses in the component exceed the strength of the component. Stress in a building component could be caused by external or Internal forces. External forces are dead, live, wind,seismic loads or foundation settlement and internal stresses are induced by  thermal movements, moisture changes, chemical action, etc.

 Cracks could be broadly classified as structural and non-structural cracks. Structural Cracks are due to incorrect designs, faulty construction, overloading or inadequate supervision and these may compromise the safety of a building. In a nutshell, structural cracks are directly seen on
 structural members such as beams, columns and slabs .    

Non-structural cracks are mostly due to internally induced stresses in building materials and these generally do not directly result in structural weakening. In course of time, some non-structural cracks may lead to structural cracks due to penetration of moisture through cracks or weathering action, this may result in corrosion of reinforcement and thus may render the structure unsafe.

 Vertical cracks in a long compound wall due to shrinkage or thermal movement is an instance of non-structural cracking. Non-structural cracks normally do not endanger the safety of a building, but may look unsightly or may create the impression of faulty work. If a non-structural crack is ignored, it could pose threat on the safety of the building on the long run.Cracks may vary appreciably in width from very thin hair cracks barely visible to naked eye (about 0.01 mm in width) to gaping cracks 5 mm or more in width. A commonly known classification of cracks, based on their width is:

 a) Thin - less than 1mm in width

 b) Medium - 1 to 2 mm in width
 c) Wide - more than 2 mm in width.

 Cracks could appear in any form, may be of uniform width or may be narrow at one end and thicker at the other end. Cracks could be straight, toothed, stepped, map pattern or random and may be vertical, horizontal or diagonal. Cracks may be only at the surface or may eto more than one layer of materials.Modern structures are comparatively tall and slender, have thin walls that are designed to carry more stress and are built at a fast pace. These structures are therefore, more prone to cracks as compared with old structures, which used to be low, had thick walls, were lightly stressed and were built at a slow pace. Moreover moisture can easily reach the inside of the modern buildings due to the usage of thin walls. Thus measures for control of cracks in buildings assume much greater importance than ever before.

Crack correction

Cracks from different causes have varying characteristics and it is by careful observation of these characteristics that one can correctly diagnose the cause or causes of cracking and adopt appropriate remedial measures. Therefore, the service of a professional is required.On a general note, few basic principles if followed would be very effective

 1.  Rendering of minor crack less that 1m wide may be done after observing the crack for some time and then sealing it with weak mortar of cement, lime and sand. 

 2.   Cracks in which width changes with season should be filled up with elastic fillers like silicon or a polyurethane compound.

 3.     Where shear crack are observed shear keys made of reinforced concrete with at least 1.5 percent steel reinforcement may be provided at 1 to 1.5m intervals.

 4. If cracks are due to movement of soil due to shrinkage and expansion (like in black cotton soil), prevention of moisture penetration in the surrounding areas has to be ensured by providing a waterproof blanket around the plinth. The masonry wall below ground level should also be separated from the adjoining soil by replacing the existing soil with coarse grain material.