You do not need a laboratory to catch most bad building material. A few simple checks, done when material arrives, can save a house owner from weak concrete, cracked plaster and damp walls. Here are the field tests site engineers actually use, and what each one tells you.
Cement: five checks in five minutes
- Manufacturing date. Every bag is printed with the week, month and year of manufacture. Cement loses strength as it absorbs moisture, so prefer bags less than about 90 days old.
- Lumps. Press the bag. It should feel smooth and free-flowing. Hard lumps that do not crumble between your fingers mean the cement has started to set.
- Feel. Push your hand into the bag. Good cement feels cool. Rub a pinch between your fingers: it should feel smooth, not gritty.
- Colour. Ordinary cement has a uniform greenish grey colour. Patches of a different shade may point to contamination.
- Water test. Sprinkle a handful on a bucket of water. Good cement floats briefly and then sinks. Material that stays floating for long may be stale or adulterated.
Sand: the silt test that matters most
Too much clay and silt in sand stops cement from bonding properly and leads to cracks and dusty plaster. Test it with a clear bottle:
- Fill a transparent bottle or measuring jar about half full with sand.
- Add water with a teaspoon of salt until the bottle is three-quarters full.
- Shake hard for a minute, then leave it for about three hours.
- Silt settles as a fine layer on top of the sand. Measure both layers.
Silt % = silt layer height ÷ sand layer height × 100. If it is more than about 8%, the sand should be washed or rejected.
Other sand checks
- Rub wet sand in your palm. If it leaves a brown stain, there is a lot of clay.
- Taste a few grains. Salty sand, often from sea or creek beds, corrodes steel and causes white patches on walls.
- For manufactured sand (M-sand), check that it is cubical and not flaky, with little dust.
Bricks: sound, drop and water
- Sound. Strike two bricks together. Good bricks give a clear metallic ring. A dull thud suggests under-burnt bricks.
- Drop test. Drop a brick flat from about one metre onto hard ground. A good brick should not break.
- Scratch. A fingernail should not leave a mark on a well-burnt brick.
- Shape. Edges should be straight and sharp, faces flat, and all bricks close to the same size.
- Water absorption. Weigh a dry brick, soak it for 24 hours and weigh it again. First-class bricks absorb less than 20% of their dry weight.
- Efflorescence. After soaking and drying, white salt patches on the surface mean soluble salts that will later stain walls.
Water: often forgotten
Water for concrete should be clean enough to drink. Water with oil, salt, sewage or high sulphate content weakens concrete and corrodes steel. If you use borewell water in a coastal or industrial area, get it tested once.
Field tests catch obvious problems. For important structures, the lab tests in the relevant Indian Standards give the final word, and your engineer can arrange them.
Frequently asked questions
Is older cement completely useless?
Not always. Cement stored well in a dry place may still be usable after three months, but it loses strength over time. Use older bags for non-structural work and fresh bags for slabs, beams and columns.
Is M-sand better than river sand?
Good quality M-sand is consistent, free of silt and widely used where river sand mining is restricted. Poor quality M-sand can be flaky or dusty, so the same checks apply.