If you have decided to make your pond from concrete then you will need to seal the top layer of render to stop the water getting in & the lime which is harmful to fish getting out. The best way to do this is with G4 Sealer. You don't need a primer; just paint it straight onto the concrete. You can also use G4 to coat flagstones waterfalls statues & other concrete products to make them safe for your pond. Clear or Black colour sealant available For a clear finish you need three coats
- a total of 550g per square metre