Anyone who has ever built a concrete rendered pond, will probably have heard of G4. Due to its cold-curing resin formula, G4 is a tough, watertight sealer for concrete, brick or porous stone ponds and is also safe for fish. 5kg of G4 is enough for three coats on an area of approximately 10m². Normal recommendations are two coats of clear G4 (which is cheaper), followed by two coats of black G4.

Bondaseal is a UV stable, non-yellowing, tough coating for sealing stonework above the waterline.

Bondaflex should not be confused with ordinary silicone sealer. Based on a cold curing polyurethane rubber, it bonds to many materials (unlike silicon which would peel off) including brick, stone, metal, most plastics, PVC and rubber pond liners. It is also non-toxic to fish when cured.