Hi, All.  first time posting here, after much of my home is finished..

12 years ago, I removed the bathtub from a bathroom, and replaced it with a large shower.  A friend had a bunch of Walker-Zanger limestone available, and did I want it?  Yes, with concerns…I laid all out, built the frame, poured the concrete base, covered it with Oatey showerpan liner, glued properly.  Tested for leaks, all was fine, and I continued with mortar bed, tile, backerboard and limestone for three walls, glass block for the 4th.  And put in a beautiful mosaic from a Lebanese factory before their war…

Everything was great until January, when my daughter and her boyfriend were in, and 4 showers were taken one after the other.  And then there was water coming thru the subfloor, dripping in the basement.  Since showers had happened like this previously, I was flummoxed, as was Oatey support.  So, I removed from around the drain to the membrane; all seemed fine.  Blocked the drain, filled the floor to about 1/2″ at the edges, and shortly thereafter, it leaked.  

I removed the remaining floor tile and mortarbed to the membrane.  The membrane had cuts in it, not associated with the removal done with an impact drill.  I cut out the membrane within maybe 2″ of the wall, and it was VERY stiff, verging on brittle, yet not everywhere.  Spoke with Oatey, who “had never heard of that before”.  Asked a tile setter, and he said, yes, he had seen it before. Imagine a corporation, saying no, when yes is the answer…Put in a new membrane as a test, gluing it underneath the existing one.  It held water where I replaced it.  Then put in more, up to the edge of the wall, and it leaked.  Got some roofing silicone, and buttered it on, up the membrane to where the backerboard started, maybe an inch or so up.  Held water.  Filled it up an inch or so higher, and it leaked…So, it is obviously a faulty membrane.  I removed the lowest section of limestone and backerboard all around the perimeter, exposing maybe 4 more inches of membrane,

So, I’m removing the concrete base tonight, pouring a new one tomorrow and sloping it appropriately.  Next week, I plan on putting the new membrane as high as I can get it underneath the existing one.  After it dries and I can fill it, I’ll do the mortarbed, and a week later go to finish the floor, which will probably come up the wall.

I have always used a good sealer on it, most recently “Premium Gold” travertine and sandstone sealer, by Superior Adhesives and chemicals,  Ut seem like I could put gallons on, and it would be absorbed.  The membrane comes up maybe 10″ on the walls.  The only concern I have is the outside curb, which is covered by the membrane to the outside of the curb, but not down towards the outside floor.  This is the only horizontal part of the shower that has limestone on it.  So, the question: is there any better way to truly waterproof this small section than stone sealer, that will look like it isn’t there?  No issues with freezing and thawing, obviously.

I want to specify here that, as an amateur and not a professional home improvement contractor, I followed Oatey’s directions to the letter, other than the outside membrane mentioned above.  I simply don’t know enough to take short cuts.