GCL pond lining in Nottingham

A clay bed where the ground is sand

Dig a pond into Sherwood Sandstone or Trent gravel and it empties. Puddling it with clay the old way needs a source of good clay and a lot of compaction. A GCL packs that seal into a roll you can carry on a telehandler: sodium bentonite held between two geotextiles, swelling when wetted into a very tight barrier.

Ecologists like it for great crested newt and mitigation ponds because the finished bed looks and behaves like clay. Plants root into the soil cover, and if a root or a heron's beak does nick the liner, the bentonite swells into the hole.

Checking the water first

A GCL isn't right for every pond, and around Nottingham the reason is often chemistry. The Mercia Mudstone east of the Trent carries gypsum, and water that has run through it can be rich in calcium, which over time can stiffen sodium bentonite and weaken its seal. Ponds fed by hard groundwater or field drains deserve the same question.

So before recommending GCL we ask what will fill the pond and what drains into it. If the chemistry, steep banks or exposed edges count against it, we'll say so and suggest a welded membrane instead. We install both.

Where these ponds are going in

Most of our Nottingham GCL enquiries come from new estates on Nottingham's outskirts, where planning asks for a mitigation or wildlife pond in the open space. Others come from restoration of old ground: former gravel workings in the Trent valley, landscaped colliery land, and country parks that want a pond without a plastic edge showing.

Laps, paste and cover

Shaping the hole is your groundworker's job; they leave us a smooth, firm formation with flints, roots and rubble taken out. We walk it and sign it off, then unroll the panels with wide overlaps, bedding bentonite paste or granules into each one. Inlets, outlets and the pond edge are dressed the same way, and our log notes every lap and detail on the day.

Timing matters on the wetter Trent valley sites. Bentonite that hydrates before it's confined is spoilt, so we hand over with the required cover depth and your contractor places the soil layer straight after.