Most patio problems start below the surface. Cambridgeshire clay holds water and shifts with the seasons, so the excavation depth and sub-base specification have to match what is actually in the ground. A compacted Type 1 granular sub-base transfers the load evenly and gives the bedding layer a stable platform to sit on. Without it, slabs sink, joints open and water finds its way to the lowest point, which is often the house wall.
The bedding method depends on the material. Porcelain requires a full mortar bed and a primer slurry applied to the back of each slab before it is placed, without both, the slab will not bond and will lift. Indian sandstone varies in thickness across a single pack, so each slab is individually bedded to bring the surface to a consistent level. Limestone and concrete slabs follow the same mortar-bed approach, with jointing compound chosen to suit the stone type and exposure.
Falls and drainage are set before any slab goes down. A laser level identifies the correct gradient so water sheds away from the house and clear of the damp-proof course. Where the garden layout concentrates surface water in one spot, an ACO channel drain or a linear outlet is specified at the same time as the paving, not added as an afterthought once pooling appears. Edge restraints are set on a compacted base to hold the finished area in line for the long term.