Fibreglass Pond Lining

Glass reinforced plastic (GRP) can be used to line ponds and, when in the right hands, can be as easy as applying wall paper! GRP is hard-wearing; resistant to weathering and temperature variations, perfect for that pond lining.

When you are looking to line with GRP, ensure the base you are covering is suitable. Is it hard wearing itself? The lining will add to the strength and rigidity but the foundations need to have a good quality level of this also. If the base is brick, make sure the cement render has time to dry fully. As a guideline, half inch cement rendering needs to be kept damp for 3 days and dried for a further 10 days after this before applying a primer coat.

GRP Toxicity and Wildlife

Early note to make, check the glass fibre being used has had the laminate and topcoat system cured properly to avoid toxic effects on the pond wildlife. Many ready made pond bases use GRP, the right method and materials can allow GRP to be non-toxic. Most polyester resins contain 35% styrene monomer which can be toxic to fish if not cured correctly. General purpose resins also mostly contain amine (0.1 – 0.2%) but is required to cure the resin even though it is classed as toxic to fish. Use a general purpose resin or Gelcoat/Resin B to help on vertical surfaces.

Pigmenting the GRP

GRP can be coloured in a wide range of colours with most ponds being black or racing green to maximise visibility of the fish. Use no more than 10% of pigment by weight when adding colour, additionally darker colours may not even need this level due to the opacity. Although, known to contain lead of which some is soluble, many Koi stockists opt for British Racing Green as the pigment is locked in to the topcoat.


Ordering Your Materials

Work out the surface area of your base that requires coating and send this to us so we can work out the amount needed. As a rough guide, using you will need 450gm per sq/m with 2.5 times the weight of the glass fibre for the resin. Allow for wastage if you are completing the project yourself and not yet a dab hand at it all! We would also suggest a very minimum of two layers of the 450gm per sq/m to ensure it is all water tight as varying factors such as the base and resin drying can weaken the lining.

For more details on how to line your pond with GRP, what to look out for and the drying processes, have a look at our full fixing guide for more information.