What Size Pond Liner Do You Need?
Before you start digging, you need to calculate the correct pond liner size. Use this simple formula: Length = pond length + (2 × max depth) + 0.6m overlap. The same applies to width.
For example, a pond that is 3m long × 2m wide × 1m deep requires a liner of approximately 5.6m × 4.6m. Our HDPE Pond Liner with free underlay is available in custom sizes to suit any garden pond.
Tools and Materials You'll Need
Before beginning your pond liner installation, gather the following:
- Heavy duty HDPE pond liner (minimum 0.5mm thickness for garden ponds)
- Pond liner underlay or protective geotextile fleece
- Spade, rake, and compactor
- Spirit level and long straight edge
- Scissors or Stanley knife
- Stones, coping slabs, or turf for edging
- Garden hose
Step 1: Mark Out and Dig Your Pond
Use a rope or garden hose to mark the pond outline on the ground. For a natural-looking pond, avoid perfectly geometric shapes. Dig out the pond with graduated shelves at 23cm (9 inches) and 45cm (18 inches) depth — these shelves support marginal plants and give wildlife an easy exit point.
Aim for a maximum depth of 60cm–90cm for most UK garden ponds. Remove any sharp stones, roots, or debris from the excavated area.
Step 2: Lay the Underlay
Never skip the underlay. Even in clay soil, sharp stones can migrate upward over time and puncture your liner. Lay a geotextile fleece or our included pond liner underlay across the entire excavation, overlapping sheets by at least 15cm. The underlay protects against stones, tree roots, and frost damage.
Step 3: Position the HDPE Pond Liner
On a warm, sunny day, unfold the HDPE liner and lay it loosely over the pond. Warm temperatures make HDPE more flexible and easier to work with. Allow the liner to drape naturally into the contours — do not stretch or pull it tight. Place rocks or pavers temporarily around the edge to hold the liner in position without creasing it.
Work from the centre outward, gently pressing the liner into the shelves and deepest point. Fold any excess at the corners into neat pleats rather than stretching the material.
Step 4: Fill With Water
Begin filling the pond with a garden hose. As the water level rises, the weight will press the liner into shape. At intervals, adjust the liner folds so that water pressure distributes evenly. Filling takes 1–3 hours depending on pond size.
Leave 15–30cm of liner overhanging the pond edge — this will be buried or weighted down in the next step.
Step 5: Trim and Secure the Edges
Once the pond is full, trim the liner leaving a 15–20cm overlap around the perimeter. Bury the overlap under turf, press it under coping stones, or weight it with decorative pebbles. For a professional finish, use pond liner anchor profiles or edging stones.
Do not trim too close to the water line — you need the overlap to prevent water from escaping behind the liner during rain or top-ups.
Step 6: Dechlorinate and Add Plants
Tap water contains chlorine which is harmful to pond fish and beneficial bacteria. Either leave the pond for 48–72 hours to off-gas naturally, or treat with a dechlorinator product. Allow the pond to mature for 4–6 weeks before adding fish.
Add oxygenating plants immediately — they help establish the pond's ecosystem and control algae from day one.
How Long Does an HDPE Pond Liner Last?
A high quality HDPE pond liner will last 30–50 years when correctly installed. Our heavy duty HDPE pond liner comes with a 40-year guarantee and UV stabilisation to prevent degradation from sunlight exposure.
Avoid using sharp tools near the liner, and keep tree roots trimmed back from the pond edge to maximise liner lifespan.
Buy HDPE Pond Liner UK – Free Underlay Included
Industrial Supplies Co stocks heavy duty HDPE pond liner in custom sizes, with free underlay included on every order. Browse our full pond liner range or order your pond liner today with free UK delivery on orders over £50.