What happens over time if the underlayment surface has irregularities?

When the underlayment surface has irregularities, it can cause noticeable imperfections in the surface of the installed tile. This occurs because tile is typically rigid and does not conform well to variations in the underlayment. As a result, any bumps, dips, or uneven areas beneath the tile can translate into visible flaws, such as cracks, lippage (where edges of tiles do not align), or even incomplete adherence, which may lead to further issues like tile breakage or water intrusion. Ensuring a smooth, even underlayment is crucial for achieving a successful and aesthetically pleasing tile installation, emphasizing the significance of proper preparation before laying down tiles.