G4 Pond Paint and Sealer Clear 5kgG4 is a moisture cured polyurethane which forms a non porous seal on concrete, brick and porous stone. G4 uses the moisture in the air and substrate to cure and harden. G4 Colours. When using coloured G4 the first two coats must be G4 clear. This is because the G4 clear provides the maximum non porous seal and adhesion. A further two coats of G4 coloured can now be added. G4 Coloured system Application 1st & 2nd coats= clear 410gram metre sq.(for 2