Car park lining in Nottingham

Keeping car park water out of the aquifer

Runoff from parking bays picks up oil, fuel drips and rubber. On Sherwood Sandstone, letting that infiltrate straight down puts it into an aquifer used for drinking water, so many engineers specify a lined system instead. The paving still filters and slows the water; the membrane stops it at the bottom of the sub-base.

The same lining suits sites on the Trent gravels with groundwater close below, on the mudstone south of the river, and on contaminated made ground where infiltration could mobilise what's already there.

The car parks it goes under

Lined permeable paving tends to appear on the larger surfaces that planning conditions focus on. Smaller schemes, such as a church hall or a GP surgery off a residential street, use it too when the plot sits on gravel or fill.

• Retail parks and supermarket car parks along the ring road
• The tram network's park-and-ride car parks
• Hospital, university and college parking
• Business parks and office car parks near the M1

Falls, outlets and edges

Shaping the formation, with its falls towards each outlet, is the groundworker's task. We walk the finished surface before unrolling anything: does every part run towards an outlet, is it firm underfoot, and has every sharp stone gone? Then a protective non-woven goes over the floor and turns up the sides.

Our membrane follows in wide panels, fused together where they meet, and that day's trial weld goes in the job record. Each outlet pipe, overflow and any duct that has to cross the liner gets its own sealed boot, and the sheet's edges are lifted and fixed at design height. A top layer of geotextile then protects the sheet from the stone of the sub-base.

Covering it promptly

Exposed membrane on a busy site is at risk from plant and other trades. We work to your programme so the sub-base follows soon after we hand over with the weld records. On a phased car park, the edge of each section can be left protected, ready for the next phase to be welded to it.

City-centre and hospital jobs often come with restricted delivery hours and live traffic next door. We agree drop times in advance and keep rolls inside the working area, out of the way of ambulances, buses and shoppers.