Leaking hairline cracks at bottom of older inground pool

Feb 12, 2019
Nashville TN
Have lived with a 18x40' - 33k gal inground pool since moving into house in 1989. Pool was built in 1983. I had it replastered in 1996. In 2011, applied a DIY epoxy coating and then a 2nd coat 2015. BTW - I've heard lots of negatives regarding epoxy, but imo if prepped and applied meticulously, the Nelsonite coating will perform well. A recoat every 5 years is not required, but also not such a big deal. Costs maybe $500 in materials and renews beautifully. Epoxy so much less maintenance that plaster.

However about 2012, noticed deep (9') end developing a hairline crack running 4' along floor and then 3' up vertical wall. Summers begin with pool holding water just fine, but as summer progresses, our clay soils dry-shrink. Crack opens up and we may lose 1-2 inches per day by mid-August. Every year - same schedule. And late September - after heat of summer - it seems to close up again.

Back in 2015, I drained and used a grinder to enlarge crack to a depth of 1/4 inch. Then filled crack with PC-7 underwater epoxy, sanded and applied epoxy coating to that area. That held without leaks for 2 years, but last summer began to leak again. I hope to drain and attempt to fix in a more permanent fashion this coming May. Looking for a better solution? Would appreciate any ideas short of structural foundation work or a torque lock system that requires I drill/chisel out . ~thanks for any ideas