We have all seen that cracks start to appear on walls after plaster work. No one likes these cracks on their walls, so in this article we are going to see the causes and the methods of prevention of wall cracks.
How to prevent plaster cracks.
Drying shrinkage cracks occur due to the rapid loss of moisture while hardening of the plaster. This excessive shrinkage creates tensile stresses and if these stresses are greater than the tensile strength of plaster, the plaster ruptures and cracks are formed.
Precautions to be taken during plaster work to avoid cracks:
Preparation of surface for plaster
Masonry wall must be well wetted with water before starting the plaster work. It’s better to start hydrating the masonry a day before plaster work. But too much water can prevent plaster from sticking to the masonry, so wet the surface accordingly. If the surface is not wetted properly, it starts absorbing water from the plaster and leads to cracks. Any loose material on the masonry wall must be removed from the surface.
Selection of Sand
Selection of the proper grade of sand plays a vital role in plaster work, since it has over 80% proportion in the mix. Sand with fineness module less than 2.2 has a high of producing cracks, so using sand having fineness module between 2.4 to 2.6 works best for the plaster. While using River sand, make sure it doesn’t have high silica (soil) content to avoid cracks.
Cement-sand proportion
Keep the Cement-sand proportion ratio in between 1:4 to 1:5. Richer mixture than this can lead to more cracks .Consider the use of fly ash blended cement because it releases low hydration heat and has a low possibility of crack development as compared to ordinary Portland cement.
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Plaster thickness
- Internal Plaster: 6mm to 12mm thick.
- External Plaster: 15mm to 20mm thick
- Ceiling Plaster: 6mm Thick.
Higher thickness than above mentioned values can lead to Deboning and Delamination.
Use of Chicken Mesh
Chicken mesh helps for better grip in plastering. Either metal wire mesh or fiber mesh are used for this purpose. The brick wall- RCC column transition is more vulnerable to cracks, so it is advisable to use wire mesh. Fiber mesh is a better option because the metal mesh may get rusty.
Curing
Cure the plaster surface for at least 7 to 10 days. Begin the curing as soon as possible if the conditions are hot and dry. While curing the water must be sprayed at controlled pressure and controlled amount since it can deform the plaster surface.
Do not over finish the surface.
Even after all these precautions some hairline cracks may appear on the surface, but its quite normal. These fine cracks can be filled while painting using putty filler.
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