Re: Tile over plaster walls in bath
I take it you installed a tub against an existing plaster wall; I did the same in my old (19th century) house. The plumbing wall was new framing, but the other two walls were three-coat plaster on wood lath. Very sound. The tub I used was an Americast with a 1" tall, but very thin flange at the top edge. I shimmed out the wet wall so the flange was buried (would not cause a bulge/flare at the bottom) when I attached 1/2" durock on that wall, to within 1/4" of the tub rim. On the two plaster walls, not wanting to add undue thickness, I applied 1/4" hardi-backer set in thinset. The whole tub surround was then waterproofed with Schluter Kerdi membrane, with the seams lapped 2". If I had it to do over again, I would totally seal the hardi with Plasterweld or Link bonding agent (a PVA_based liquid), so that the thinset stayed workable; hardi really sucks the water from mortar, making the task of bonding the Kerdi really too difficult for a slow DIY- tiler. The tile went on the kerdi just fine, and I know that it is totally waterproof.
Remove not the ancient landmark, which your fathers have set.