I am going to be tiling the face of my fireplace with 16x16 travertine tiles. As the tiles are quite heavy , I am concerned with proper adhesion. The face is made of cinderblock bt has been painted with an unknown type of paint. I was told that a fortified thinset would be fine but also have heard that using a liquid nail or similar would be better for this application. is this true? I plan on supporting the tile until the thinset / adhesive has set but don't want future problems. The fireplace does not get much affect from heat as it has a gas insert.
One option is to put cement board over the existing surface and then put your tiles on that. Works great and there is no worry about the thinset paint interface failing.
I don't trust paint in these situations and have seen the thinset pull the badly applied paint off the cinder block surface. While it is not a big safety issue it is always a pain to have to go back and do the same job over.
My idea of a perfect day: No where to go and all day to get there.