Map cracking can be due to plastic shrinkage as can the horizontal cracks which form at corners and between windows Drying shrinkage cracks are the result of moisture loss after the plaster has hardened. Cracking which results when an excessive amount of water is lost from the plaster in the first hours after the application is known as plastic shrinkage cracking. Glass fiber tissue can also be applied during painting. These cracks can be filled with a proprietary filler and painted over. When the cracks are noticed while the plaster is still plastic, they are often floated closed, only to reappear sometime later. Not using building lime or masonry cement when the sand lacks fine material.Use of a sand that is badly graded, and lacks fine material (less than 5% by mass passing the 0.075 mm sieve).Suction into the walls if the bricks are absorbent and they have not been dampened.Evaporation if the wall is not protected from sun and wind.These cracks normally occur when a plaster mix with a high cement content is used or the plaster is allowed to dry too quickly.Ĭauses of excessive early moisture loss are: Map cracking is similar to crazing except that it is usually deeper (sometimes going through the plaster) and the hexagons of the pattern may measure up to 200 mm across. If necessary, glass fiber tissue can be applied during the painting operation. Craze cracks are of little importance, do not open and close with time, and can be covered using reasonable quality paint. Crazing often occurs within a few hours of the plaster being applied to the wall and cracks may hardly be visible until dust or moisture makes them noticeable. They are usually the result of over trowelling a rich mix (one with a high cement content) or using sand containing an excessive amount of dust (more than 15% by mass passing a 0,075 mm sieve). They are usually very fine and shallow and do not extend through the whole depth of the plaster. Non-structural cracksĬrazing is a network of fine cracks, usually in a hexagonal pattern, which measures between 5 and 75 mm across each hexagon. The causes and repair methods for each are discussed below 1. Defects most frequently noticed in the wall plaster fall into one of the following categories This write-up is aimed at site engineers and supervisors who wish to assess whether plaster is acceptable, and if not, what can be done about it. Moisture or water absorbed into the walls – if the blocks are very dry and water-absorbent or have not been dampened before plastering might cause drying shrinkage cracks. Cracks in the wall plaster are caused due to various reasons: Rapid evaporation of water, if the wall is not protected from sun and wind, can cause map cracking or dry shrinkage cracks.
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