GCL pond lining in Worcestershire

A clay bed without the puddling

Field ponds in Worcestershire were traditionally puddled with local clay. A GCL does the same job factory-made: sodium bentonite needle-punched inside a pair of fabrics. Once buried and wet, the clay swells tight enough to hold a pond, and should a reed root find its way through later, the swollen clay closes round it.

That suits wildlife ponds, nature-reserve scrapes and SuDS ponds on housing schemes where the landscape architect wants marginal planting and a soil finish rather than a visible membrane edge.

When we'd steer you away from it

Some Worcestershire ponds are better off with plastic, and we will tell you if yours is one. The clay must stay pressed down under soil or water, so shallow, rounded profiles suit it and steep, bare banks do not. The water itself also counts. On the Cotswold edge around Broadway, where water comes off limestone, and wherever a pond takes runoff from roads or yards, we look at what the water carries before recommending clay over membrane.

Where the answer is no, a welded membrane does the job instead. We install both, so the advice follows the pond rather than our preference.

Laying the panels

Clay mats are unforgiving of lumpy ground, so ruts and loose stone on the bed are what we look for first. We inspect the ground your contractor has prepared and flag anything angular before a roll comes off the lorry.

• Formation signed off: smooth, compacted, free of sharp stone
• Rolls deployed with generous overlaps
• Paste or granules of bentonite worked into each overlap
• Inlets, pipes, edges and structures detailed in bentonite
• A running log of each lap and detail

Cover follows quickly

Our handover note gives the minimum soil depth over the mat, with the QA sheets. Spreading that soil, wetting the clay and filling the pond fall to your contractor. Bentonite wetted before it is confined swells loosely and loses its seal, so we time the handover to when your cover material and plant will be on site.