· Cement
Mistake 1: inaccurate measurements
Estimating is almost always done from the drawings, and the drawings almost never match what is built. A wall that measures 12 metres on paper may measure 12.30 on site; multiplied by the height and by every wall on a floor, that difference becomes pallets.
The fix is simple and almost nobody does it: measure on site before closing the order. When the element does not yet exist — a slab still to be poured, for instance — measure the erected formwork, not the drawing. And deduct real openings, not those of the original design.
Mistake 2: ignoring changes and adjustments
No project is built exactly as drawn. A door moves, a floor level changes, a service appears that was not there, the client asks for a modification mid-build. Every adjustment consumes material that was not in the estimate.
The mistake is not that changes happen: it is estimating as if they would not. A reasonable margin over theoretical consumption — varying by material and by type of work — is part of the estimate, not a luxury. In materials with high waste, like mortar or adhesive, that margin matters more.
Mistake 3: buying insufficient quantities
It is the consequence of the previous two and the most expensive. Running out of block mid-day stops the entire crew. Running out of concrete mid-slab creates an unplanned cold joint. Running out of adhesive with half a floor laid forces an interruption at a point that will show later.
The real cost is not the missing material: it is the extra freight, the idle crew hours and, at worst, a permanent defect in the element. Buying 5 % too much is almost always cheaper than being 5 % short.
How to estimate properly
Start from real dimensions taken on site. Deduct actual openings. Add each material's inherent waste. Leave margin for the adjustment that always appears. And buy by stage, not all at once: cement waiting three months under a tarpaulin takes up moisture and loses capacity.
One useful reference figure: with the 20×40 cm face you get about 12.5 blocks per square metre before deducting openings, plus waste and joint thickness. But every material has its own arithmetic, and that is where leaning on the supplier pays off.
The supplier as part of the estimate
Reviewing drawings and requirements is part of the service, not a favour. A supplier who only dispatches what is asked for adds nothing; one who checks consumption by stage and flags when the quantity does not add up saves more than they charge.
And there is an advantage to concentrating the order: when material comes from one place, deliveries are scheduled around site progress rather than around the availability of three different suppliers. Freight is paid once and there is one point of contact for the whole project.
