Car park lining in Worcestershire

Why so many car parks here are lined

Much of central and southern Worcestershire sits on red mudstone or Lias clay, and drainage designs for new car parks around Worcester, Droitwich, Evesham and Redditch reflect it. The paving still lets rain through the surface, but the aggregate below holds it on a sealed membrane and releases it to the sewer or a brook through a controlled outlet.

Even on the free-draining sandstone further north, an engineer may specify lining where the car park is near buildings, over made ground, or above groundwater that needs protecting.

Typical sites

Car park lining in the county tends to come with commercial and public schemes rather than farms or villages.

Many of these are in town centres with tight access, so we agree delivery times and a laydown area for the rolls before we arrive, and can line a car park in sections where part of it has to stay open.

• Supermarket and retail car parks in the market towns
• Staff and visitor parking at business parks off the M5
• Parking courts on new housing estates
• Schools, surgeries and community buildings
• Service yards where the lined sub-base links into a crate tank

How the liner goes in

By the time we arrive the dig is trimmed to its falls. We walk it first, looking for high spots, loose flints and anything that won't drain to the outlets. Non-woven fleece is rolled across the bottom and lapped up each side wall, and the impermeable sheet goes over it in panels, each joint fused with heat.

A trial weld is logged, every outlet and pipe through the sheet is sealed, and the edges are brought up to their finished height. Another cushion layer then goes over the top, so the first loads of stone can't damage the plastic.

Handing back to the groundworker

Once the weld records are complete, the formation is yours again for sub-base and paving. Covering the liner promptly keeps it safe from site traffic, so we fit our visit to the date the paving gang is due to start. On a phased retail or housing scheme, we come back for each area as it is dug rather than leave lined formation waiting under open sky.