ProjectCalcCalculators in this cluster
What this cluster is for
A paved surface is three materials stacked in a trench: a compacted sub-base, a bedding layer, and the slabs themselves with their joints. The paving calculator covers all three, because pricing one without the others is how a patio job stalls halfway through.
The number people get wrong is the slab count, and they get it wrong in a particular way. Slabs are laid on a module — the slab plus its joint — so a 6 m run of 600 × 600 mm slabs with 10 mm joints takes ten slabs across, not ten metres’ worth of slabbing. Do the sum as area ÷ slab area and you finish a row short, which you discover on the last course.
What usually goes wrong
- Counting slabs by area. The joint is part of the module. Widening the joint from 10 mm to 15 mm can add a slab per row on a long patio.
- A sub-base too thin for the traffic. 100 mm for a patio, 150 mm for a car, more for a van or for soft clay under the surface.
- No fall. Roughly 1:60 to 1:80 away from the building, set in the sub-base and the bedding rather than by tilting individual slabs.
- Sharp sand confused with building sand. Bedding is sharp sand: it compacts evenly and does not shrink away. Building sand belongs in mortar.
- Forgetting the cuts. A diagonal or curved layout wastes more slabs than a rectangle of the same area, and the offcuts are rarely reusable.
- Drainage that nobody planned. Where a hard surface sits between the front wall and the highway, the permitted-development position on permeable surfaces comes into play.
What to order together
- Slabs, MOT Type 1, sharp sand, and a brush-in polymeric jointing compound
- Edging or kerb units and a concrete bed for the free edges
- A geotextile membrane under the sub-base on soft or clay ground
- Hire: a plate compactor, and a disc cutter for the cuts
Related clusters
Cross-links here are contextual, not a second home: each calculator belongs to exactly one cluster above.