Concrete based ponds need a final render sealing to stop the water getting in and lime leaking out. G4 has been long established as the market leader for this task.when using the black paint, 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 black can now be added, making a total of 410g per square metre clear and 400g sqm black.the amount of g4 you will need depends on the internal dimensions of your pond. For example let's say the pond is 3m x 2m and 1m deep. Br 1 work out the area of the bottom by multiplying the width and depth in metres in our example 3 x 2m 6sqm. Br 2 find the area of one of the sides depth multiplied by width or length then multiply by 2 to cover both sides in example sides 1 2 x 1 2sqm x 2 4sqm. Br 3 find the area of the other pair of sides in example sides 2 3 x 1 3sqm x 2 6sqm. Br 4 add up sides and floor 6sqm 4sqm 6sqm 16sqm. Br 5 multiply total by 550gsm 16 x 0.55kg 8.8kg.