Pond liner, sealer, or something else?

goz83

I have a small pond in my front garden approx 6' x 5' x 4' deep. I used a liner and it has been good for 2 years, but I am planning to build a larger pond out my back yard maybe next year and I would like a bit more freedom with what holds the water in the pond. I expect that it will be holding at least twice the volume of water in the existing pond, which has a shelf all around the edge about 1 foot down. I keep goldfish, a couple of koi (nothing expensive) and 2 terrapins recently introduced/rescued. I think liners are a bit too restrictive. If i want to install a window in the pond, for example, the liner is pretty much out, or will complicate things and likely show more bends and folds.

I was thinking about using fibreglass. I see it advertised on donedeal for roofs and i know it can be used for tanking and boat repairs, but what about a pond? Any thoughts? The pond will be above and below ground, most of it below, maybe 2 feet above ground and 3-4 feet at the deepest level. I plan to have the filtration external, with the pipes being fed under ground to a diy 3part filter system, of gravel, bio and then UV. The pump itself will also be external and the waste will be sucked from the deep part of the pond, with an isolation valve to drain from a higher level in the winter time. The pond will most likely be concrete and i plan for it to be a 2-tier pond, maybe with the upper level housing plants and will be used as a waterfall to help oxygenate the main body of water. I would guesstimate the dimensions to be 4'x10'x2, descending to 6' in the main pond area. The upper tier will be maybe 4x2x1 and will be supported by concrete pillars maybe 4' above ground level, with the filtration system partly buried and hidden beneath the raised tier.

I just don't know what I should use to seal the pond at this point. Any tips there, or in other areas are welcome.

goz83

Bump.