Speaking from personal experience of similar bathroom problems in my
last house, I would personally go thew whole hog. If you already have a
double layer of tiles there, take them all off, get a friendly local
plasterer to come and skim thew wall for you then retile properly.
You'll be surprised how cheap skimming is, I was when I got it done ,
and the nice flat new wall will be a lot better to tile onto.
Tiling above the double layer of tiles and using a shower is going to
cause problems when the water runs in behind the top layer, which it
will, which is startling when they all fall off when you are in the
shower (yep, it happened!).
Go on dad, an afternoon with a bolster and hammer will get those tiles
off and another day putting new tiles on that nicely skimmed wall is
what you're there for ;)
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