I have a 600 gallon above ground fish pond in my backyard that I have always wanted to do a mosaic on. The outside layer of the structure is OSB but the top half of that has the pond liner hanging down over it. The finished mosaic would be 9 feet long and just over 3 feet high.

I'm thinking cement backerboard would be a good foundation but am not sure what to use as an adhesive and grout. We get pretty snowy winters so it would have to be able to stand up to cold and wet.

Any advice for me would be appreciated!