Geotextile Protective Underlay

What is a Protective Pond Underlay?

Geotextile protective underlay is a tough, non-woven fabric placed beneath (and sometimes above) the pond liner to protect it from punctures and abrasion caused by stones, roots and ground movement.

Geotextile 250gm underlay is a mechanically bonded polypropylene needle punched material. This is a high performing, tough underlay relative to some brands available on the market.

Do I need a pond underlay?

We always recommend installing a heavy-duty geotextile underlay beneath the pond liner. Underlay protects against sharp stones, roots and ground movement, helping maximise the life of your pond liner and reducing the risk of punctures.

A protective underlay also acts as an escape route for any gasses that may build up under a pond liner.

If you intend on covering your pond liner with soil, gravel, rocks or concrete, it is advisable to add Geotextile protective underlay both above and below the liner to prevent costly and time consuming repairs.

What Does a Pond Underlay Protect Against?

A protective underlay liner is recommended for all pond liner installations. It will protect your pond liner from:

• Sharp stones
• Flint
• Rubble
• Tree roots
• Ground movement
• Uneven soil
• Animal burrowing
• Installation damage

Liners Online guarantee all our pond liners when used with this protective liner.

Geotextile is supplied in rolls of 2 metre widths. 

Benefits of Geotextile Pond Underlay

• Helps prevent punctures
• Protects against sharp stones
• Reduces damage from roots
• Extends pond liner lifespan
• Suitable for all pond liner materials
• Rot resistant
• Easy to install
• Lightweight yet extremely strong

How Do I Calculate How Much Underlay I Need?

If you know what length and width of underlay liner to order, then add them to the relevant boxes above by using the drop downs, or if you are not sure how much to order, then go to our pond liner size calculator and add in the exact measurements of your pond and the calculator will work out how much you need to order to avoid waste or disappointment.

Customers should follow this calculation to order the correct dimension for your pond. The 0.15m overlap or overlay is the minimal amount and a guide depending on the type of edging you have planned:

• Maximum pond length + (2 x depth) +2 x 0.15m overlap = Total Length of Liner

• Maximum pond width + (2 x depth) + 2 x 0.15m overlap = Total Width of Liner

Multiplying the depth by 2 accounts for the depth on both sides of the pond. And, the same applies to the overlay. If you intend adding planting shelves to your pond design, they don’t need to be accounted for in the calculations because they won’t significantly affect the pond measurements.

Building a garden pond and installing a bottom drain or fountain pump? Save on postage by adding waterproof sealant to your pond liner and pond underlay order.

How to install an underlay liner

Installing a protective underlay and pond liner is straightforward with a little preparation. Start by excavating your pond to the required shape and depth, ensuring the top edge is level all the way around. Carefully remove any sharp stones, flint, roots or other objects that could damage the liner over time.

Before laying the liner, we strongly recommend installing a heavy-duty geotextile underlay. The underlay provides additional protection against punctures caused by stones, roots and ground movement, helping to extend the life of your pond liner.

Once the underlay is in place, carefully unfold the Butyl pond liner and drape it evenly over the excavation, allowing an equal overlap around all sides of the pond. Gently ease the liner into the contours of the pond, smoothing out smaller wrinkles and neatly folding any larger pleats without stretching the material.

Begin filling the pond with water slowly. As the water level rises, continue adjusting the liner so it settles naturally into the shape of the pond. When the pond is completely full, leave it for at least 48 hours before trimming any excess liner or completing the edging. This allows you to confirm that the liner has not been damaged during installation and has settled fully into position.

Once you are satisfied everything is watertight, finish the pond edges using your chosen materials. If using paving slabs or coping stones, ensure they overlap the pond liner by at least 51 mm (2 inches) to conceal and protect the liner from sunlight and accidental damage.

Expert Tip: Never install a pond liner directly onto bare ground. Even soil that appears free of stones may contain hidden flint, roots or debris that can puncture the pond liner over time. A quality geotextile underlay is inexpensive compared with the cost and disruption of repairing or replacing a damaged pond liner.

Common Mistakes When Installing Pond Underlay

• Not removing sharp stones.
• Using old carpet instead of geotextile underlay.
• Not protecting the pond liner beneath heavy rocks.
• Stretching the underlay too tightly.
• Leaving gaps between sheets on underlay.
• Not covering pond shelves properly.