We tried the polymer first and that was not successful. I do not blame the product - more likely user incompetence or mis-guided / imprudent preparation / application. My best guess is that the polymer is ideally suited to sealing leaks; less so for initiating the sealing of a pond basin that is sure to leak, because of the soil strata / conditions.
The bentonite supplier had visited the site, some years earlier and was not sanguine about the chances of success. (The project was started in 2007!) More recently - after the failed polymer test effort - I did a small test, using two bags of bentonite and decided - based on the results - that a whole-of-pond effort was worth trying.
Those two bags were applied as a light slurry. The more recent 9.5 tonnes were simply barrowed in and spread with a rake.
There are some awkward-sloping, so difficult-to-seal-with-bentonite areas around the edge of the pond, at the present water level, which may be leaking. We have half a tonne of bentonite left, so we may may try some of the remaining polymer on those places, if we exhaust the bentonite supply.
