Three millimetres. That was the tolerance specified for the concrete slab base of a new sludge storage tank at Yorkshire Water’s Askham Bryan treatment works. The programme was eight days. It was finished in five.
Precision concrete work doesn’t leave much room for the usual adjustments that get made on a job as it progresses. Once the shuttering is set and the pour begins, you’re committed — which means everything before that point has to be right. Timber formwork was installed and checked against laser levels before any steel went in, and the reinforcement was inspected continuously throughout placement rather than reviewed at the end. The design was intricate enough that positioning mattered at every stage, not just overall.
The pour itself was controlled to avoid displacing either the formwork or the reinforcement, and the finishing process was where the tolerance was either met or missed. It was met. Across the full slab, within the 3mm specification.
Yorkshire Water noted afterwards that the work was well organised and carried out to a high standard, and that the team respected their site safety rules and left the area clean on completion. That last part matters more than it might sound on a working treatment site.
Eight days on the programme, five days to completion. The tank has its base.
