Thanks lycopus. A freshwater Nostoc seems to fit. I guess this is similar to some of the terrestrial slimes that I've occasionally seen, but this is the first one in sheet form that I've noticed under water.

I'm new here, joined just this past weekend, but my input would be to leave well enough alone. Hindsight being 20/20, perhaps you'd have done it differently. And in the future, you will. In this case, you didn't, and as DH often tells me, ''if-dog-rabbit.'' Saving $400 to not use the waterproofing at the outset and now to consider throwing an additional $2000 at the completed project, for a fix that would potentially be the most half-assed way to do it, seems questionable to me. On top of that, the original work was done by a man with a good reputation and messing with it at this point might cause him to withdraw his original workmanship guarantee. Honestly, you have the best of all worlds right now. You were lucky enough to have a good worker to begin with, saved the original $400, plus you have the opportunity to check in the situation behind the walls to catch any problems in their infancy. Enjoy the shower, save your $2000 and maybe use it to go on a trip.

The highest rated via Robinson test Crack isolation/uncoupler membrane is still Nobleseal TS and CIS if you have an issue with elevation and other membranes are to thick look at Noble. As CTEC stated Ditra is almost always my last choice for multiple reasons .

Yes, we used Kerdi board, the membrane, and the pre-molded forms and corner blocks. We hired a contractor who had taken Schluter training and was experienced in the application, so they provided the material. Do you have a nearby ProSource? They can get you everything you need to do it yourself if you want. Cement board and RedGuard like the previous poster mentioned is a viable alternative. This was our 2 time to gut that same bathroom to the studs with leakage issues from cement board and plastic liner installations, so we took no chances on doing it right this time.