The Night Tripper wrote:

Hi All
We had our bathroom tiled a few years ago. Recently I have
noticed that some of the bottom row of wall tiles - the ones butting up to
the bath - have rung 'hollow' when tapped. Even more recently I noticed
that the grouting between these was failing. So since I have a few days
free (ha!), I have had a closer look. Ended up by pulling of two or three
off this bottom row. They came off pretty easily ;-(.

Underneath there seems to be a thick layer of pink-ish plaster (I don't
know my plaster types very well, sorry) slapped onto the (solid) wall
behind. This plaster is very friable, I easily scratched deep hatch marks
into it with a 50p piece. Images he

http://www.nicorp.co.uk/download/DSCF1856-1.JPG
http://www.nicorp.co.uk/download/DSCF1857-1.JPG

Now I don't know if the plaster is friable because water has got at it, or
it was friable for some reason anyway and that has allowed the tiles to
loosen. It looks like the pink plaster was put on in the first place to
level the wall up - though even with that, the tile adhesive was only
touching it in a few places on each tile, as I think you can see from the
pictures.

I have some spare replacement tiles, and obviously I'm now keen to make
this
all good. I'm presuming it would be best to chisel off this rubbish
plaster and replace it (with what?), put on to the right depth so that the
replacement tiles will adhere across their whole surface.

Any other ideas or suggestions?

Thanks a lot
Jon N

I know it's kind of my default answer, but soak the plaster in 1:2 diluted
SBR a couple of times. It will stabilise it to a few mm depth. The reattach
tiles with fresh adhesive.

I had some polished plaster which BAL instructed (for BAL Green anyway) to
both scrach (wire brush) prime with dilute SBR to stabilse and achieve a
better bond. I had a couple of walls done in one-coat which is softer than
regular gypsum so I primed that too. The result was quite significant - a
mauch harder finish afterwards.

--
Tim Watts