We have an old, 12” x 12” linoleum tile floor in the kitchen. The floor has many missing/broken tiles, raised bumps and depressions here and there and a bare piece of plywood covering an old heat register. My Mother is insisting that we can simply tile right over WITHOUT new underlayment. We go through this every 6 months. Is there anyone that agrees with her? I need help bringing her to her senses. I refuse to do a crap job.

You can do it but it won't last,lol.Your best bet it to just redo it with floating floor,inexpensive easy to put down and no underlay plywood needed.You can get floatinf floor that looks like oak for about 99 cents a sq ft that is 8mm thick.Good luck with mom.

Well you are correct of course. Any imperfections in the under layment will telegraph through the tile, assuming vinyl tile. A new surface of 1/4" plywood is just the most efficient way of getting a good smooth surface to work width. Glue and nail or screw, lots of glue and don't lay the plywood too tight. Something tells me that your mother is buying the material and you are providing the labor.

What type of tile are you thinking of using?