I have been building an urbanite raised bed, which is going to be a wicking bed eventually. Looking at the pointy concrete chunks, I think that an EPDM liner would end up in trouble. What if I put mesh against the walls and bottom and troweled cement over them? This would also be cheaper then a plastic or rubber liner, and less likely to be toxic.
It should work, with a good rich mortar mix. You might not even need the mesh for most of it. Your urbanite has plenty to bite onto.
Worst case, you have made a smooth liner for the EPDM.
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