everyone has been a great help so far, just a final recap before actual work happens: our house is old but solid, joists then 2×12 subfloor with 3/8″ plywood. there is a bit of rot on one 2×12. it runs part way under a wall and is 90% still there so i feel it would be best if i could leave it and fill it with some kind of patch, then put new 3/8″ plywood on top. a neighbour suggested ‘Poly Underlay Plus’ floor leveler (cement based)? The floor feels solid. Code suggests 1-1/8″ min. thickness which we have. Is this good enough? I have dug out 2001 issue of FHB on ‘Installing a Leakproof Shower Pan’. He suggests that over the SOLID sub-floor goes: thinset to bond the mud to the subfloor, mud layer pitched at 1/4″ per ft., felt paper, membrane/liner, 2.5 to 3″ mud for base for tile. Does the thinset go on top of the mud to glue the tile to the mud? Is this system still look like the way to go? Kind thanks, mIchael hollihn, prana timber frames