If you were installing a pond in an urban garden that is 20m x 7m how big would you make the pond, (I am currently thinking 3x5 x1-2 deep) and presuming the clay level is too low to seal naturally, what would you use to seal the pond. Looking forward to posting some pictures and some mock up designs of the garden also if anyone has a nice resource for urban pond making that would be much appreciated. Thanks Jack
EPDM as Pak says, if you can afford it. Some wicking bed, aquaponic people use LDPE (which can be a thicker form of builder's plastic) or builder's plastic doubled over on carpet. Depends on the pond's use too. If you want it to last, you pay for it. Some use pigs, gley, bentonite and other methods. Some work, some fail.
Never is a very long time Pak, are you sure about that? Environment: The product contains a substance which is toxic to aquatic organisms and which may cause long-term adverse effects in the aquatic environment. EPDM safety data sheet (PDF) https://pcs.federalmogul.com/MSDSSh...ubber3b3b2823-108a-4d3a-bf18-d71a6582c4fb.pdf