Gordon Low Custom Box Welded EPDM Pond Liner

Custom box welded EPDM pond liners

A liner shaped for your pond, without the bulky folded corners

A carefully built rectangular pond deserves a neat finish inside as well as out. A box welded pond liner, also called a box weld liner, is made into the shape of your pond before it arrives, with a flat floor and four fitted walls. Rather than folding a large flat sheet into each corner, you position the shaped liner inside the prepared structure.

We supply these made to measure liners from Gordon Low, the manufacturer behind our existing EPDM liner range. Choose 0.75mm or 1mm EPDM and enter your finished internal length, width and depth in millimetres. A 100mm top flap around the perimeter is included as standard.

What makes a box welded liner different?

Gordon Low fabricates its tailored liners in the UK, using fully overlapping factory seams that are hot bonded and vulcanised. The shape is created at the factory rather than assembled from separate sheets on your pond build. The finished membrane still has seams; it is not a moulded plastic shell or a seamless rigid tank.

On a correctly measured, properly prepared pond, this gives straight walls and tidy corners without the excess corner pleats of a flat sheet. It is a particularly useful option for formal garden ponds, raised koi ponds and builds where the inside of the pond will be clearly visible. A good fit depends on accurate measurements and a suitable supporting structure.

Fewer bulky folds also mean fewer awkward pockets where settled dirt and organic debris can collect. The tailored walls and corners are easier to see and reach when cleaning, giving a neater, cleaner-looking pond. This is a practical maintenance benefit, not a replacement for good circulation, filtration and routine pond cleaning; the liner does not prevent fish-health problems.

EPDM versus butyl: why we choose EPDM

Butyl is a familiar name in pond building, but it is not the only quality rubber liner option. We choose pond grade EPDM for these made to measure liners because it combines flexibility with excellent resistance to UV light, ozone and outdoor weather conditions.

• Flexible material: EPDM is pliable during fitting and remains a flexible membrane in service. That is useful when positioning a shaped liner inside a prepared pond.
• Made for outdoor conditions: SealEco identifies resistance to sunlight, ozone and temperature extremes as key properties of its pond liner material.
• Suitable for pond life: the specified pond grade EPDM is suitable for fish and aquatic plants. This is purpose made pond lining material, not an unspecified roofing membrane.
• A tidy tailored finish: Gordon Low forms the liner to the agreed dimensions with factory bonded seams, avoiding the bulky corner folds of a flat sheet.

What should I compare when choosing EPDM or butyl?

Both EPDM and butyl can make good pond liners. Butyl is also a flexible rubber material. For a useful comparison, look at the actual membrane specification, thickness, seam construction, warranty terms and what is included in the quotation, rather than choosing on the material name alone.

For this range, our choice is Gordon Low EPDM in 0.75mm or 1mm, made to your measurements with a 100mm top flap. It brings together the material properties we want for an outdoor pond and a neat factory formed shape. The fitted shape comes from the fabrication, not from EPDM alone.

Flexibility is not a substitute for accurate sizing or protective underlay. Never stretch the liner across gaps or suspend it from the coping. Support and protect the base and walls throughout.

0.75mm or 1mm: which should I choose?

Both options provide a flexible EPDM lining. The 1mm option has a thicker membrane; the 0.75mm option is the lighter choice. Neither thickness replaces protective underlay, a sound pond structure or careful installation. If you are unsure which suits the build, tell us about the pond size, construction and intended use before ordering.

Measuring your rectangular pond

Use our box liner measuring diagram to identify the length, width, depth and included top lip. The calculator gives an instant price for the liner you configure, including VAT. Check all three measurements carefully before adding it to your basket.

1. Measure the finished inside, not the outside of the blockwork. Allow for the final surface preparation and lining arrangement. If the pond is not yet built, treat the calculator as a planning price and measure again when the structure is ready.
2. Record the internal length and width in millimetres. For example, enter 3000 for a 3 metre length. Check at several points. If dimensions vary or the corners are not square, send us the measurements for review.
3. Measure the full lining depth. Measure from the finished base to the top of the wall where the flap will turn outwards. This is not simply the intended water depth.
4. Do not add the standard flap to these measurements. The 100mm outward flap is included separately. Do not add an allowance for welding or subtract a fitting tolerance yourself.
5. Check the details before manufacture. Include the position of any window, drain, pipe penetration or other feature when discussing the final specification. Keep a copy of your agreed measurements.

My pond has shelves or an unusual shape. What should I send?

We can arrange a bespoke liner quotation for ponds of any shape or size. Get in touch through our contact form with a clear, fully dimensioned plan. Include a plan view and side sections with every length, width and depth written down in millimetres. Show each shelf width and its height from the base, steps, slopes, recesses and the required top flap. Mark the location and dimensions of any window, drain or pipework. Photos help explain the build, but they do not replace measurements.

We will review your plan and confirm the design and price with you. Please do not price a stepped pond as one large rectangular box, as it will not describe the liner you need.

The included 100mm top flap

The flap turns outward over the top edge of the pond. It provides an overlap for finishing beneath the coping stones, helping retain the top edge as part of the completed coping detail. It does not support the weight of the water or replace the structural walls.

Check that 100mm is suitable for your wall, window and coping arrangement. If you need a wider overlap or a different edge finish, ask for a bespoke quotation before ordering. Settle and fit the liner in accordance with the installation instructions before permanently fixing the top edge.

Planning a pond viewing window?

A box welded liner can be used as part of a pond build with a viewing window, provided the window assembly is designed for a liner installation. The glass support, frame or rebate, liner connection and sealing detail all need to work together. The standard liner price does not include a window opening, factory fitted flange, glass or window sealing components.

Tell us about the window before the liner is made. Do not cut an opening until the fitting method has been agreed. Browse our made to measure pond viewing glass, or send us the window and pond plans together so we can help you plan the components.

Prepare the pond before the liner arrives

This is a flexible lining, not a freestanding tank. The pond needs a stable structure with continuous support to the floor and walls. Remove sharp debris and projections, finish the surfaces appropriately and use suitable protective pond underlay. Check the underlay specification with the installation requirements for your build.

Have enough people available to handle the liner without dragging it over rough edges. Follow the supplied fitting instructions, align the formed corners and let the liner settle without pulling it tight. Drains, pipe flanges and windows require their own compatible sealing details. They are not automatically included just because they appear on a pond plan.

Made to measure lead time

Please allow approximately 2 to 3 weeks for manufacture, depending on how busy the factory is and when the measurements and specification are confirmed. This is a guide, not a guaranteed delivery date. More involved designs may need additional time. If you are working towards a particular installation date, speak to us before booking trades or draining an existing pond.

Questions before you order

Will it remove every small ripple?

The tailored shape avoids the large folded corners needed with a flat sheet. EPDM remains a flexible material, so small ripples can depend on the fit, supporting surface and installation. It should not be tensioned like a rigid shell to chase a perfectly flat appearance.

Can I include protective underlay?

Yes. Select black heavy duty underlay in the calculator and we will recommend suitable Gordon Low black 250gsm underlay packs using your pond measurements. We allow for the floor, all four walls and the top edge, with 100mm overlaps in our cutting allowance. The calculator shows the pack size, quantity, underlay price and combined total before you add anything to your basket.

Underlay comes as flat material in standard 2 metre wide packs, not as a shaped box. Cut and overlap it to fit during installation. The recommendation covers one protective layer beneath the liner, not a second layer above it. Selected packs are added as a separate basket item using their current website price. If you already have suitable underlay, choose liner only. Coping, glass, fittings and installation are not included.

Can I use this calculator for a pond with a sloping floor?

No. It assumes one flat rectangular floor and a constant depth. Send the slope, high and low points and all wall measurements for a quotation that describes your actual pond.

What if I need to change the measurements?

Contact us straight away. Because the liner is made for your pond, a change may not be possible once fabrication has begun. Please check the final dimensions carefully before approving manufacture. Ask us about the applicable made to measure terms and manufacturer warranty before ordering.

Box-weld or flat sheet: compare the fit and price

For a 5m long × 4m wide × 1.5m deep rectangular pond, allowing 500mm beyond each edge gives a flat-sheet planning size of 9m × 8m. The nearest suitable available sheet may be larger: a 10m × 8m sheet covers that estimate. Some extra material forms the folds and edging, and some is trimmed; it is not all discarded waste.

The box-weld version is made to your pond’s finished internal dimensions, with our standard 100mm top flap. It avoids the bulky corner pleats needed to shape a large flat sheet. Accurate measuring, continuous support and careful fitting are still essential; flexible rubber can retain small ripples.

Example: 5m × 4m × 1.5m rectangular pond — liner-only prices including VAT

EPDM thickness	Available flat sheet covering a 9m × 8m estimate	Made-to-measure box-weld	Box-weld price difference
0.75mm	10m × 8m — £899.99	£1,447.89	£547.90 more
1mm	No suitable listed sheet. Price a custom 1mm flat sheet.	£1,679.18	No like-for-like listed sheet price available

The flat sheet estimate allows 500mm beyond each edge; the shaped liner includes a 100mm top flap. These are different edging details. Prices above come from the current listed options when this page loads; check the selected product for final price and availability. Underlay, fittings and any delivery charges are not included in this comparison.

For your own measurements, calculate your box-weld price above and open its flat-sheet comparison. You can follow the link to a suitable listed option and decide whether the price difference suits the finish you want.

A flat sheet can be the more practical choice for a pond with curves and shelves. Browse our 0.75mm EPDM sheets, 1mm EPDM sheets, or use our pond liner size calculator. Compare the same thickness and check your actual edging detail before ordering.

The measuring diagram and liner illustration are guides, not photographs of the exact liner supplied. The diagram is not to scale. A box welded liner needs supporting pond walls and a base; it is not a freestanding tank.