G4 Pond Seal is a moisture cured, , one component polyurethane which forms a non-porous, tough, durable but flexible seal . Seals porous substrates such as concrete, brick and porous stone. G4 will not seal concrete block or lightweight block, these need to be cement rendered before application of G4. It generally is advised that all down to 0°C and in areas of relatively high humidity. G4 cannot be used on bitumen but it will not damage butyl rubber liners. G4 is easy and quick to use, simply brush on the recommended 3 coats in a day.