We’ve all seen cracks start to appear on walls after plasterwork, and no one likes these unsightly blemishes. In this article, we’ll discuss the causes of wall cracks and how to prevent them.
Causes of Plaster Cracks
Drying Shrinkage Cracks
occur due to the rapid loss of moisture while the plaster is hardening. This excessive shrinkage creates tensile stresses, and if these stresses exceed the tensile strength of the plaster, cracks form.
Preventing Plaster Cracks: Essential Tips
Preparation of Surface For plaster
Wetting the Masonry Wall: Ensure the wall is well wetted with water before starting plaster work. It’s best to start hydrating the masonry a day before plastering. However, avoid over-wetting as it can prevent the plaster from sticking to the masonry. The surface should be moist but not drenched.
Removing Loose Material: Clear any loose material from the masonry wall to ensure a clean surface for the plaster to adhere to.
Selection of Sand
Proper Grade of Sand: The sand used in plastering plays a crucial role. Sand with a fineness module of less than 2.2 is more likely to cause cracks. Using sand with a fineness module between 2.4 to 2.6 is ideal.
River Sand Considerations: Ensure that river sand doesn’t have high silica (soil) content to avoid cracks.
Cement-Sand Proportion
Ideal Ratio: Maintain the cement-sand proportion ratio between 1:4 and 1:5. A richer mix can lead to more cracks.
Use of Fly Ash Blended Cement: This type of cement releases low hydration heat and has a lower possibility of crack development than ordinary Portland cement.
Plaster Thickness
Internal Plaster: 6mm to 12mm thick
External Plaster: 15mm to 20mm thick
Ceiling Plaster: 6mm thick
Avoid Excessive Thickness: Higher thickness than these values can lead to deboning and delamination.
Use of Chicken Mesh
Better Grip: Chicken mesh (metal wire mesh or fiber mesh) helps provide a better grip for plastering.
Transition Areas: The brick wall-RCC column transition is more prone to cracks, so use wire mesh here. Fiber mesh is preferable as metal mesh may rust over time.
Curing
Proper Curing: Cure the plaster surface for at least 7 to 10 days. Begin curing as soon as possible if conditions are hot and dry.
Controlled Water Spray: Spray water at controlled pressure and amount to avoid deforming the plaster surface.
Avoid Over-Finishing
Do Not Over-Finish: Over-finishing can lead to cracks and surface defects.
Dealing with Hairline Cracks
Even with all these precautions, some hairline cracks may still appear. These fine cracks are normal and can be filled during painting using putty filler.
By following these steps, you can significantly reduce the occurrence of cracks in plaster walls, ensuring a smooth and durable finish.
For more detailed guides on construction and maintenance, visit our Construction Zone.
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