Collection: Pond Liner Accessories UK | Underlay, Sealer & Installation Supplies

A pond liner installation is only as good as the accessories used to support it. Our range of essential pond liner accessories includes everything required for a complete, professional installation — from 200gsm geotextile underlay that protects your liner from day one, to waterproof concrete pond sealer for existing concrete ponds. Get every product right the first time, and your pond will perform for decades without issue.

Pond Liner Underlay — Why It's Essential

Geotextile underlay is not an optional extra — it's a critical component of any pond liner installation:

• 200gsm geotextile — the UK industry standard for garden pond installations. Heavy enough to provide real protection, light enough to handle easily.
• Protects against sharp stones and roots — even apparently smooth ground hides hazards that can puncture a liner over time
• Guards against ground movement — seasonal freeze-thaw cycles can shift ground; underlay cushions your liner against this movement
• Extends liner life — abrasion from below is the most common cause of gradual liner failure; underlay eliminates this
• Use under all liner types — EPDM, butyl, HDPE, and PVC all benefit from proper underlay protection
• Double up on very rocky sites — install underlay both under and over the liner when ground conditions are particularly aggressive

Pond Concrete Sealer

If you have an existing concrete pond, or are building a new concrete pond, our waterproof concrete pond sealer is an essential product:

• Stops lime leaching — fresh or old concrete releases calcium hydroxide (lime), which is highly toxic to fish. Sealing is not optional — it's life-saving.
• Standalone waterproofer — can be used as the primary waterproofing for concrete ponds that don't require a liner overlay
• Underlayer for liners — seal concrete before laying a pond liner for belt-and-braces waterproofing
• Apply 2-3 coats — allow each coat to fully dry before applying the next. Full cure time is typically 24-48 hours per coat.
• Compatible with all liner types — safe to use beneath EPDM, butyl, HDPE, and PVC

How Much Underlay Do You Need?

Calculating your underlay requirement is straightforward:

• Same area as your liner — use the same length × width calculation as for your liner
• Add 10% for wastage — overlaps, cuts, and trimming consume material
• Overlap sheets by minimum 15cm — join strips with no gaps to ensure complete coverage
• Use our pond liner calculator — enter your pond dimensions to get exact material quantities for both liner and underlay

Accessories FAQ

Do I really need underlay under my pond liner?

Yes — underlay is essential for protecting your liner and extending its life. Even on apparently smooth or sandy ground, sharp stones, root tips, and ground movement will cause abrasion and eventual puncture without underlay protection.

What gsm underlay do I need?

200gsm is the industry standard for garden ponds and is suitable for most ground conditions. Use 300gsm or heavier on rocky ground, sites with aggressive root systems such as near trees, or commercial installations.

How do I use concrete pond sealer?

Clean and dry the concrete surface thoroughly. Apply 2-3 coats using a brush or roller, allowing each coat to dry fully before the next. The sealer forms an impermeable barrier that prevents lime leaching — critical for fish safety in concrete ponds.

Can I use any underlay with my pond liner?

No — use dedicated geotextile pond underlay only. Carpet underlay retains moisture and can rot or harbour bacteria. Sand shifts and settles. Non-woven fabrics vary enormously in quality. Only purpose-made geotextile underlay provides reliable, long-term protection.

How much sealer do I need for a concrete pond?

Coverage varies by product and surface porosity, but typically 5 litres covers 10-15m² per coat on a prepared concrete surface. Order sufficient for 2-3 coats. New or very porous concrete will absorb more sealer than weathered surfaces.