I've been compelled to rip out my shower in my master bath after a tile fell inwards.
I've got the tiles and old backer board off, studs exposed.
Examining the shower pan, I think I have a problem. My understanding of how a shower pan is constructed, is there are effectively 3 layers above your foundation concrete. There's a dry pack / deck mud that establishes your drain slope, which extends from your drain collar to the walls of your shower. When installing the dry pack base, you want to already have your wall material for your tile in place (concrete board or similar). Then there's an impermeable membrane, like a sheet of PVC tarp material. This extends up the wall a few inches. Then on top of that there's another concrete layer consisting of mortar over the PVC material, also sloped to the drain. Finally, you install your flooring tile over that and then tile the walls.
I have the following problems to resolve.
#1: The currently installed impermeable membrane has gaps at the entry curb where the door goes. This appears to be the primary moisture invasion route and it rotted out the two stud supports that support the shower door and its wall. It appears the previous builder did not extend the membrane to the curb at all, definitely didn't use dam corners for trickier sections or anything like that.
#2: The membrane was installed behind the backer board rather than in front of it. Here I'm a bit baffled. It appears this shower pan was constructed by building the pan first with no tile backer board installed initially. Concrete board was then applied for the lowest 2 feet of the shower, sandwiching the membrane between the studs and the concrete board, then a fibrous backer board used for everything above the concrete board. I suspect the weakness of this design is that moisture was able to get behind the concrete board due to the membrane being behind the concrete board, and also that the concrete board wasn't in place when the dry pack/membrane/mortar pan was built. Every Youtube video I've watched of building a new concrete shower pan shows the order of operations to be one of two ways: wallboard, drypack, membrane, mortar... or drypack, membrane, wallboard, mortar. This one appears to have been built drypack, membrane, mortar, wallboard. The only seal around your wall/floor junction is then grout, which is rather prone to failure. If you have your wallboard in place before putting your floor mortar down, it seems to me you have a better seal against water intrusion.
#3: My drain that extends above the top of the top mortar layer has stripped holes for the drain cover screws. The existing drain that was in the floor was circular, and all the replacement shower hardware we have chosen is square shaped and we want to change the drain to be a square shaped drain. This requires us to chisel up the existing drain anyways, since the drain cover screws are stripped.
I'm struggling with a plan to go forward and could use some advice. I've been trying to use an air hammer to pull up the layer of mortar above the PVC membrane, but that appears to be insufficient to the task. I got a concrete disc for my 4.5" angle grinder and that does seem to cut faster, but I created such a cloud of concrete in the bathroom that I had to leave the room for the last hour after only making a series of cuts in the concrete around the drain fixture. Haven't been back in yet to see if I've hit the depth of the membrane or not. It's going to take a lot of cutting to segment up the floor so it can come out with the PVC membrane if I continue with that tactic.
What's the best way to disassemble a concrete shower pan while preserving whatever work is worth preserving? I imagine I don't want to cut into or remove the dry pack layer that is there (if it's indeed there in this installation). I assume it will have bonded thoroughly to the foundation below it and will be more or less impossible to separate from the concrete below it.
I suspect taking a sledgehammer to the floor would be damaging to the dry pack under the mortar I want to remove. That and it's kind of a tight area anyways, slinging a sledge isn't a good option.
