I have Varnish - I'm sure I could get liquid nails (already have a caulking gun). I intend to varnish the cieling, and I may just have to put a thin coat of liquid nails on the back of all the side tiles - they just will not stick (I sanded, and then vacuumed the surfaces prior to adhering them.) I already planned to seal the seems with silicone, to keep moisture from getting under the tiles. Would silicone work to adhere them? I have tested out a few thing on the scraps, and puncturing the tiles deforms them, even if you use a drill. They warp and bend a little.