This is an effective sealer for concrete ponds. G4 is a moisture cured, one component polyurethane product which forms a non-porous, tough, durable but flexible seal on concrete. This prevents lime leaching into your pond from the concrete and stops water leaking out. You just paint it straight onto the concrete, no primer needed. G4 can also be used to coat porous flagstones, waterfalls, statues and other concrete products to make them safe for the pond. For a black finish you need two coats of clear and two coats of black. Thats 440g per square metre of clear and 400g per square metre of colour.