Lining the pond hole

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When you have dug the pond profile the next step is lining the pond hole with a watertight membrane.

Underlining for the pond hole:

  • Before Underlining - Remove any sharp stones.
  • Line the hole with an underlining geotextile. This will uphold the guarantee for the liner you use.
  • Underlining is sold in 4 or 2 metres width and you order as many linear metres as you need.
  • Cover all shelf areas and up stands.
  • This does not need to be laid in one continuous piece so patch some corner areas from overlap pieces cut from another corner.
  • Cut out overlapping layers rather than leave thick, bulky folds.
  • Geotextile only needs to be one layer thick.

1. Geotextile underlining     2. Polyethylene liner material    3. Butyl rubber lining

Lining the pond hole with flexible liner material:

  • There are many choices of flexible liner materials:
  • Butyl rubber - can be heavy to work with but stretches nicely around curves and is a dull grey/black colour and is available with a 30 year guarantee.
  • Woven polyethylene - carries a 30 year guarantee but is a cheaper initial purchase.
  • This is lighter to work with but has no stretch so requires careful folding into curves and corners.
  • Reservoir liner for larger field ponds or bad terrain is made from polyester reinforced PVC and is rot proof and root penetration proof but is more expensive.

To calculate the size of lining material needed:

  • Measure the overall length, width and depth of the hole including the height of your vertical upstand above the top shelf
  • You need to buy:

length to order = the length + twice the maximum depth + 60cms spare
width to order = the width + twice the maximum depth + 60cms spare

To fit the lining:

  • Loose lay the flexible liner in the pond hole.
  • Walk into the pond in socks to put the liner flat onto the whole base of the pond.
  • Work the spare liner down onto each shelf in turn from the spare at the top without stretching taut at this stage.
  • Allow equal amounts of spare liner on all sides
  • Start to fill with water.
  • If possible use collected rain water.
  • If this is not possible then use tap water with the addition of Chlorine Guard. This eco-friendly treatment removes the chlorine, chloridamines and heavy metals in tap water which are not ideal for plants or wildlife.
  • As the water fills its weight will pull the liner into position.
  • Stop filling at every shelf level and rearrange the liner. Make sure there is sufficient for that shelf width without stretching the liner.
  • Start to pull out the creases on a curve or arrange the folds.
  • Do each shelf level in turn.
  • Stop adding water before you reach the top garden shelf level.
  • On the top edging shelf the liner will finish vertically (upright) and the surplus will lay out on the garden level.
  • Finish the folds.
  • Make sure that the 'behind' side of any fold is always higher than the finished water height.
  • One low side of a fold (even on the unseen side!) will always dictate the maximum height of water your pond will hold.

Trap the liner in place in the next step. See our page: Edge an informal wildlife pond.