Understanding the Bulking of Sand

Bulking is the increase in the volume of a given mass of sand caused by a thin film of water pushing the sand particles apart. In Mumbai, where humidity is high and sand is often stored in the open, bulking can increase sand volume by up to 25-30%.

The Risk to Your Project:

If your contractor measures sand by volume (using 'farahs' or boxes) without accounting for bulking, the actual amount of sand in the mix will be much lower than required. This results in a 'lean' mix that is cement-heavy, leading to excessive shrinkage cracks in your new plaster or concrete repairs.

Field Test for Site Supervisors:

Fill a glass jar 2/3 with sand, measure the height, then flood it with water and stir. The sand will settle to its true volume. The difference between the two heights is the bulking percentage. At Urban Civil Services, we strictly monitor these ratios to ensure every batch of concrete meets the M25 or M30 design strength.