I want to put some tiles on the wall behind the stove. The wall has plaster and is currently painted with a water-repelling paint. My idea is to sand off the paint and tile onto the plaster.
Now, I was checking the wall in preparation, and when I knock on the area that will hold the tiles, it sounds hollow in the top 15-20 cm or so, see here:
Pressing the wall I cannot notice any "give".
Is this a problem that needs to be fixed first, or can I tile on top of this?
Regardless, is it possible to fix it without redoing the plaster? I'm thinking, drill a few small holes and inject a low-viscous glue of sorts.
Any tips are appreciated.
PS: this is not a drywall. It is a brick wall covered with 2 layers of plaster. The house is old (110 years) but the top layer was done about 6 years ago.