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Originally Posted by kerry edwards
I'm thick. Can you explain the role of the membrane/coating? What difference does it make whether the thinset is on the membrane or the concrete? Won't water get thru the grout anyway if it is porous? What stops the tile from popping off the membrane/coating the same way it has popped off the concrete? I was under the impression the membranes were used to waterproof the floor itself. In this instance, it's a solid concrete floor that's been a shower for 75 years.
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The membrane collects the water that permeates through the grout lines and the thin set mortar...this water is collected by the membrane...the membrane is sloped towards the center of the shower stall to a special drain that has small "weep" holes along its outer edge to allow the water/moisture to drain...if this moisture does NOT drain, it will just sit there...and slowly work its way through the cracks/weakness points in your mortar until it breaks down...unlike the membrane which is some sort of plastic, or in the old days lead, concrete itself is porous...it will hold water...so the moisture that soaks through the grout lines and through the thin set mortar just soaks into the concrete and holds the moisture...
The key is the weep holes along the drain that allows the moisture to run off, and the membrane that acts as a big basin to collect the water and direct it towards the weep holes...with the concrete, it just acts as a big sponge and holds the moisture...which will sooner or later cause the thin set mortar to weaken and your tiles start to pop off...YOU NEED TO REMOVE THE MOISTURE THAT SOAKS THROUGH THE GROUT LINES AND UNDERNEATH THE TILES!!!