To reline a garden pond, empty it, remove the old liner, add underlay, fit the new liner with seams sealed, then refill and replant.
Why Relining Works And When To Do It
Dropping water levels, a brittle sheet, or repeated patch failures point to replacement. Patching one hole can leave hidden splits that spread. A fresh sheet resets the pond, improves edges, and lets you add cushions beneath to resist stones and roots. Choose a cool, dry spell so adhesives grip and wildlife pressure is lower.
Tools And Materials You’ll Need
Tape measure, marker paint, shovel, wheelbarrow, heavy shears, soft broom, underlay felt, new liner, seam tape and primer for EPDM, protective gloves, waders, buckets, a spare pump and airline for holding tanks, dechlorinator, and a straight plank for checking level. Gather everything before you drain so the site never sits exposed longer than needed.
Choose The Right Liner Type
Rubber sheets like EPDM and butyl bend well and suit irregular shapes. Reinforced polyethylene is light and strong with fewer folds on large spans. PVC is budget friendly but less elastic and can crack with age. Pick thickness for your pond size and wildlife load. Thicker sheets handle rock shelves and dog paws better.
Table: Liner Options At A Glance
| Material | Strengths | Watch-outs |
|---|---|---|
| EPDM Rubber | Flexible, fish safe, easy seams with tape | Heavier; needs primer for tape |
| Butyl Rubber | Similar feel; durable | Costly; less common in shops |
| Reinforced Polyethylene | Light, tough, fewer folds | Stiffer in tight corners |
| PVC | Low price, easy to source | Shorter life; prone to cracking |
Plan Timing, Wildlife Care, And Access
Work in early spring or autumn when heat is lower and plants can be lifted and set back with less stress. If fish live in the pond, arrange a shaded holding tub. Move them with pond water, run an air stone, and cover the tub to prevent jumps. Stop feeding two days before the move to cut waste. If the pond is wildlife only, scoop amphibians to a shallow tray with weeds and keep them cool and shaded.
Measure The Hole And Order Enough Sheet
Take length and width at the widest points. Add twice the maximum depth, then add extra overlap for coping stones and anchoring. Add at least 30–45 cm overhang on all sides. Order matching underlay felt. Extra felt helps on shelves and under stone edging. For a step guide to constructing ponds, see the RHS project page.
Relining A Garden Pond: Step-By-Step Method
Drain, Save Water, And Lift Plants
Pump into barrels or a clean pool for reuse. Keep a few buckets of the old water with filter sponges to seed bacteria later. Lift baskets and label them. Store marginal plants in damp trays. Net any remaining creatures as the level drops.
Remove The Old Liner Safely
Cut along the edge and peel back. Lift stones with care to avoid tearing the hole walls. If the old sheet is fused to roots, slice it free. Don’t stack sharp rubble close to the hole. Bag scraps so wind doesn’t blow fragments into beds.
Prepare The Base Like Fresh Ground
Rake out stones, glass, and roots. Shape shelves for baskets and create a shallow beach for wildlife access. Lay damp sand only if you need to smooth local hollows; a clean felt underlay gives better protection without shifting underfoot. Brush the base so nothing sharp remains.
Lay Underlay Felt
Start at the deepest point. Overlap pieces by a hand’s width. Run felt up the sides and over the rim. Stuff offcuts behind big rocks or under coping stones where extra cushion helps. Check for debris.
Position The New Sheet
Unfold near the center and drop the slack evenly. Push corners into place with flat palms. Avoid stretching. Let the sheet find the shape; folds should lie neatly like pleats. Add a little water to help the liner settle into shelves before you fix edges.
Join Seams The Right Way
If one sheet isn’t enough, clean, prime, and bond joints with the maker’s system. EPDM tape needs primer on both faces, firm rolling, and a check pass with an air nozzle to spot loose edges. Keep adhesives off dirty or wet surfaces. Follow cure times before loading with stones or full water. For EPDM taping and air-lance checks, follow the PondGard installation guide.
Set The Edge Detail
Pick an edge style that suits the garden: turf rolled over a trench, stone coping on mortar, or a gravel beach. Each needs a generous upstand of liner above water level for a splash margin. Hide the rim but keep a path for overflow so rain can exit without washing soil into the pool.
Refill Without Shocking Fish Or Plants
Use stored pond water first, then top up from the tap through a dechlorinator. Match temperature well. Add baskets as you fill so roots settle at the right depth. Let pumps run only after the water covers their intakes.
Return Fish And Wildlife Safely
Float bags or tubs to equalize temperature, then release. Hold feeding for a day, then resume lightly. Watch gill movement and behavior. Cloudiness is normal for a short time as fine silt settles.
Common Mistakes To Avoid
- Placing new sheet over the old one: trapped grit can puncture the new membrane and the build-up creates creases that chafe.
- Skipping underlay: felt is cheap insurance against stones and roots.
- Tight edges: leave slack so seasonal movement doesn’t pull seams.
- Rushing seams: unclean or unprimed joints fail.
- Harsh cleaners: bleach or solvent residues harm fish and plants.
Step-By-Step Relining Guide
- Set up shaded holding tubs with a pump and air.
- Pump down and save top water.
- Lift plants and wildlife and label baskets.
- Remove the failing sheet and edge stones.
- Rake and reshape shelves; remove debris.
- Lay felt underlay up the sides and over the rim.
- Drop in the new sheet; settle folds with a little water.
- Join any overlaps with the maker’s tape and primer.
- Set the edge detail and anchor the rim.
- Refill, add dechlorinator, and replant.
- Reintroduce fish once temperature matches.
How To Size Liner And Underlay
Convert all dimensions to meters. Use: length + 2×depth + overlap, width + 2×depth + overlap. Add 0.3–0.45 m for the overlap figure. For irregular pools, measure in two axes and pick the biggest values. Going one size up saves returns and gives spare strips for step pads or wildlife ramps.
Table: Quick Sizing And Ordering Checklist
| Item | What To Measure | Tip |
|---|---|---|
| Liner length | Longest span + 2×max depth + overlap | Round up to the next roll size |
| Liner width | Widest span + 2×max depth + overlap | Keep spare for edge repairs |
| Underlay | Match liner dimensions | Order 10% extra for corners |
Edge Finishes That Last
For turf edges, dig a small trench behind the rim, tuck in the sheet, and fold turf over. For stone, bed coping on a strip of mortar with a soft layer beneath to avoid punctures. A gravel beach needs a buried board or stone row to stop gravel creeping down the slope. Keep the water level below the hidden rim so waves don’t wick out.
Seams And Tape: Pro Tips
Clean with the recommended cleaner, not white spirit. Prime both faces and let it flash off until tacky. Apply tape, peel the film, and roll hard with a hand roller. Check edges with compressed air to spot any flutter. Any loose bits get re-rolled.
Refill Strategy And Water Quality
Use as much saved pond water as you can. When topping up from the mains, neutralize chlorine with a conditioner or trickle fill over several hours. Fit a spray bar or fountain to boost oxygen during the first day, then set normal flows. Test ammonia and nitrite before moving fish back if the pause was long.
Planting Back For Cover And Clarity
Set oxygenators deep, lilies on a shelf that suits their spread, and marginals near the beach. Aim for about a third plant cover at peak growth. Shade cuts algae, and roots trap silt. Use baskets with aquatic compost topped with gravel so media stays put.
Leak Checks And Early Maintenance
Mark the filled level and leave it overnight before fish return. Small drops can be splash or soak-in. If the level keeps falling, feel around edges for damp soil that points to a wick point. Trim stray liner only after a week, once everything has settled.
When To Call A Pro
Huge creases you can’t flatten, repeated seam failures, or unstable banks need specialist help. Contractors have lifting frames for big stonework and can weld large sheets for fewer joins on complex shapes.
Safety, Access, And Waste
Fence off the work area if children or pets are around. Keep walk boards over soft ground. Bag old sheet and offcuts for proper disposal. Return rocks slowly and watch your fingers: wet stone is slippery. Keep electrics well away from puddles.
Troubleshooting After The Refill
- Surface scum: skim and run more aeration for a day.
- Milky water: let the filter run and avoid heavy feeding.
- Slow leak: check around the rim for wicking behind stones.
Proof You’re Following Best Practice
Use a build guide for underlay, liner handling, and taped seams. Follow the maker’s method on cleaning, priming, rolling, and testing joints. For wildlife ponds, stick to advice that keeps shelves shallow, edges gentle, and water free of chlorine before plants and creatures return.