Hyderabad: Civil engineers say that filter-sand is not recommended even for plastering of walls as it leads to cracks in a short period.
Consumers, especially those constructing independent houses, may not be aware of the danger of using this type of sand and are attracted by its low price.
Chief Engineer of the Greater Hyderabad Municipal Corporation (GHMC), K Suresh Kumar, says that filter-sand is not recommended for any major construction except flooring.
“This sort of sand consists of more soil and leads to cracks in a structure. The life of constructions like pillars, columns, putting, beams, RCC slab and even plastering that use filtered-sand will be short; it will soon start flaking," he said.
He said 'manufactured sand' instead of filter-sand should be used. "Manufactured sand is prepared from stone. The manufacturers follow the rules while manufacturing such sand. It should be noted, though, that stone dust is not stone sand. Stone sand has a shape," he explained.
A structural engineer from Nagarjuna Construction Company (NCC) said that natural sand has a smoother texture with a better shape.
"Moisture is trapped in between the particles in filter-sand and so it is not good for concrete purposes. The silt and soil in this sort of sand is above what is permitted and that weakens the cement. Minimum permissible silt content in sand is 3 per cent and the maximum is 5 per cent. But filter-sand will have 20 per cent to 40 per cent of silt content. Besides silt, other particles like grass, clay lumps, tree bark are high in filter-sand against the permissible level of 2 per cent. The silt, soil and clay lumps in concrete structures will lead to collapse of walls," the engineer said.
