Placing Protective Fleece Under EPDM Pond Liner

Installation & Maintenance

In brief

Always place protective fleece directly under EPDM pond liner to prevent damage from roots and stones. Lay the fabric with a minimum of 20 cm overlap and carefully follow the contours of the pond for optimal protection and longevity.

The Function and Choice of Protective Fleece

The protective fleece forms an essential buffer layer between the subsoil and the pond liner. Due to its fiber structure, the fabric distributes the pressure from sharp objects over a larger surface. This prevents stones, debris, or growing tree roots from piercing the liner.

For a standard sandy soil, choose a fleece of 200 g/m². This offers sufficient protection against normal loads. For an uncertain subsoil with a lot of debris or stones, a heavier variant of 500 g/m² is necessary. Never use organic materials such as old newspapers or carpet. These rot away under the ground, causing the protective function to disappear and the soil to subside.

Calculating Dimensions for Underlay

Measure the maximum length and width of the excavated pond pit. Take into account the deepest points, because the fabric must follow the entire bottom contour. Use the same dimensions as for the pond liner.

Use the following calculation rules:

  • Length = pond length + (2 x depth) + 70 cm margin
  • Width = pond width + (2 x depth) + 70 cm margin

The margin covers cutting loss and edge finishing. When using multiple strips, always calculate extra material for overlapping the seams.

Step-by-Step Placement of the Underlay

  1. Thoroughly check the excavated pond pit. Remove all sharp protrusions such as stones, glass, and roots. Firmly tap the walls to prevent later subsidence.
  2. If necessary, apply a layer of 5 to 10 cm of white sand (building sand) to the bottom and terraces. This provides an extra flat base and better distribution of pressure.
  3. Lay the protective fleece in the pit. Start at the deepest point and work towards the edges. Make sure the fabric fits well everywhere on the subsoil and is not taut in the corners.
  4. Overlap adjacent strips by at least 20 cm. This prevents gaps from forming if the ground shifts or settles slightly later.
  5. Temporarily place heavy stones or tiles on the edges and plateaus to hold the fabric in place.
  6. Roughly cut off excess material with scissors, but leave enough edge until after placing the liner and filling the pond.

Common Mistakes

  • Leaving sharp objects in the pit. Even small stones can eventually press through the liner due to the enormous water pressure.
  • Using the wrong material. Old carpet, blankets, or newspapers decompose over time. Synthetic protective fleece is rot-free and durable.
  • Too little overlap at the seams. If the ground settles, the strips slide apart and the liner lies directly on the unprotected subsoil.
  • Stretching the fabric too tightly. This creates hollow spaces in corners or at depth differences. The water pressure later forces the liner and the fabric into these spaces, which causes tension and tears.
Installation