How to Tell If My Subfloor Is Rotting Under Tile?

Start by walking across the tiled area with bare feet. Pay attention to any tiles that feel bouncy or flex when you step on them. A solid subfloor should feel firm and stable. If a tile moves even slightly, moisture may have softened the wood beneath.

Look closely at the grout lines. Cracks, gaps, or crumbling grout can let water seep down to the subfloor. Darkened grout often signals trapped moisture. Also check for tiles that are cracked or have popped up. These are clear clues that the subfloor may be rotting.

• Spongy or springy tiles underfoot
• Visible cracks in tiles or grout
• Grout that crumbles when touched
• Musty or earthy smell near the floor
• Discoloration or dark spots on grout
• Tiles that sound hollow when tapped

You can do a simple tap test. Gently tap a coin or a small tool on the tile. A hollow sound suggests a gap or air pocket, which often means the subfloor has pulled away. Compare the sound with a tile that feels solid.

Another check is to press firmly on the tile with your hand. If you feel any give, that is a warning sign. You can also place a level on the floor to see if it is uneven. A slight dip or slope can indicate the subfloor has sagged from rot.

Rotting subfloor can be tricky to spot, and the damage may be worse than it looks. A professional can use moisture meters and other tools to see how far the water has spread. They can also identify the source of the leak, which is key to preventing future damage.

Repairing a subfloor usually involves removing the tile, replacing the rotted wood, and then installing new flooring. This is not a simple DIY job. The pros have the right equipment and experience to handle it safely. They can also address any mold that may have developed.