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.