I have used a product called Coprox that we get in South Africa. One type you mix with normal plaster (which I did) and then I painted with the Coprox masonry waterproofing agent. It has a type of a cement base that infiltrates the plaster. I used their darkest colour- charcoal, but it is too light for me, although everyone assures me that once the water is in, the colour will be better. I wanted to add a black stain, but was too scared that it might harm the fish.

This weekend I will plant ferns, etc under the water fall and fill the pond, just hoping it will not leak!

Albie