I have a 25 year old shower. 4x4 tile set on 'drywall' board (whether the board is green or not is unclear). Ceramic tile extends from ceiling to the shower pan. The pan feels like nylon, not acrylic or plastic. The caulkline at the pan failed. The board curled at the lowest course of tile. I want to repair the board and reinstall the original tile. I know this will never look perfect. I am simply trying to put something in place that will last a few years - long enough to do a full room tear out (this shower is adjacent to a whirlpool, all of which has the same 4x4 tile).
I have removed all of the tiles on the lowest course accept three or four which are holding like they are welded in place (these are at the corners). I cracked two of the tiles and plan to glue them together with ceramic epoxy (I know, not perfect, but should hold if I get the field right). I removed what i believe was mastic from the tiles using my wire brush wheel and have scrubbed the resulting steel marks from the tile backs.
The underlying wall is missing or damaged but remains strong and the tiles are well-adhered on the second course. The tiles that remain in place are all at the corners. As such there is nothing to which I can attach a new board or lathing. This segment of wall that is missing or damaged is extremely narrow: 1/4" on one wall and about 3/4" on the other two.
From my other reading of this site the likely recommendation would be to remove more of the wall (2 feet?) and peel back an additional course beyond that, laying in greenboard or Densguard, joining with tape, and covering with thinset. That seems like a lot of work for 3/4" gap. Plus I remain concerned I will damage tiles in the process given they are so strongly adhered. The current tile pattern has been discontinued so additional tile is not available for purchase.
I was wondering if I could lay in some steel lathing and fill the space with a setting compound of some sort. My problem is I don't know how I would attach the lathing at the ends.
The other option would be to lay in some greenboard. I'd still have the problem of 'floating' ends and would also have a joint to seal with no room to lay in mesh. One solution would be to back-fill behind the 'floating corners' with something that would set up (spray foam?) and simply caulk the seams. Might that hold for a couple years?
I'm attaching some pictures with closeups of the areas in question and a wider shot of the wall/pan. Sorry they are a little blurry - photos while squatting are not my strength.