we patch 1st after cleaning the cover w/membrane,,, then, because i hate sending guys to dig more, we overpatch ( cement, trowel, & another membrane ) ice barrier would have strength sufficient for your patch
Joe: That doughnut and Shania Twain have something in common. I won't mention it here, but it has to do w/ accessibility.
Itsreally: Yeah, the 12" was only under the assumptions given. That is a world of settling; glad Tim only has 1/16th", and long ago. 3/4" had me worried.