After getting the surface of your pond build as smooth as possible it's time to line it with pond liner underlay. Believe us - after all the effort of excavating a pond it is a false economy to go without underlay. The weight of the water when it enters the pond will soon show up any groundwork imperfections - don't take the risk! here we show how our pond liner underlay was installed.
No matter how smooth you can get the pond surface it is always worth installing a good pond liner underlay. The underlay has two jobs: First it protects pond liners from puncture from small stones and sharp edges, secondly it acts as a root barrier – preventing roots from growing and penetrating the pond liner from underneath.
For our pond we used PondXpert pond fleece pond liner underlay. At 200gsm this is a heavyweight fabric that resembles a thick fleece blanket. It is of needle-punch construction so provides plenty of cushioning. A bonus is that the felt naturally snags against the rough ground, hugging the surface and quickly matching the contours of the pond. This pond liner underlay is grey in colour with speckles of other coloured fabric – it is manufactured out of recycled fibres which means that it is environmentally friendly. We have worked with underlays in many colours from black to white – even red on one occasion. In these circumstances the colour really does not matter as it will be hidden under the pond liner anyway.
The pond liner underlay should be opened out to shape. Typically underlay will be supplied as pre-cut pieces. The industry standard is 2m (6’ 6”) and our pieces of fabric were 5m long (16’ 4”) and 8m long (26’ 3”). Simply roll out enough underlay to cover the pond base and side then cut along the length when happy
Push and pull the piece of underlay into shape – make sure it covers the area including any overlap where edging stones might be laid later. Then get your next piece of pond liner underlay (a new piece or the surplus from the original length). Lay this piece against the original pond liner underlay length so that it overlaps by a few inches. (If you don’t overlap it then a sharp edge could push through the gap).
Keep covering the pond basin with underlay until the entire construction is covered. This will provide a strong foundation for the next stage – installing the pond liner.