In article 83becdac-08b4-4309-a84e-
,
says...
Thanks guys....

The concrete was to be used to strength with the fibreglass over it.
However, with the second option, I could just put the fibreglass. Not
sure about the weight though.. I suspect I might still need something
under it for strength.

As for the waterfall absorbing the water, I have been thinking about
this. Another issue is, ultimately, I want a little stream to a second
pond (where the pump will actually be). This will obviously mean a lot
more water is needed before it starts recycling. Waterfall needs
filling, the stream needs filling etc. The bottom pond will be deep
(for volume) but have shallow / rocky sides so you won't see the water
level drop drastically.

To aggravate the situation, I don't intend running the pump all the
time. This means I cannot "get it started and top it up".

Maybe I am being to ambitious

You can get around the problem by designing it as a series of ponds in
which the water stays when not flowing but with drops between ponds
(which can be large small or stream shaped)
If it were me I would definately use butyl and construct with rock/s
Cement is fine, either seal/neutralize with ising glass (spell?) or fill
and drain a couple of times at the start.
Levels, water loss, and not hiding the edges are the main dangers, tying
it in to the rest of the garden can be tricky (it always looks better on
a natural slope.)
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea