Symptoms
- Discoloration or dark staining on tile or grout near the tub
- Soft or spongy feeling on the floor when stepped on
- Musty smell near the bathroom fixture
- Cracked or missing caulk at the tub-to-floor joint
Likely causes
- CommonFailed caulk seal between the tub and floor tileCracked or missing caulk lets water from showers or baths seep underneath repeatedly.
- CommonGrout deterioration allowing water penetrationPorous or cracked grout near the wet zone lets water through to the subfloor.
- PossibleA slow leak from tub or shower plumbingLeaks inside the wall or under the tub can wet the subfloor from below without obvious surface signs at first.
- PossibleToilet wax ring failure nearbyIf a toilet is close to the affected area, a failed wax ring can also be the moisture source.
What to do
- Inspect the caulk line where the tub meets the floor tile for cracks, gaps, or mold.
- Press on the floor near the tub to check for soft or spongy spots, which suggest the subfloor has absorbed water.
- Remove old, cracked caulk with a utility knife and clean the joint thoroughly before it dries.
- Apply a fresh bead of mildew-resistant bathroom caulk, smoothing it into a clean, continuous line.
- If a nearby toilet could be the source, check its base for looseness or staining as a separate potential leak point.
- For any soft subfloor found, treat this as a bigger repair; tile and possibly subfloor sections will need to come up to dry and repair the area underneath.
- Once the source is fixed and the area is dry, replace affected tile and grout to fully seal the floor again.
Tools and parts
- Utility knife
- Caulk gun
Mildew-resistant bathroom caulkSearch: “mildew resistant silicone bathroom caulk”
When to call a pro
Call a plumber to rule out a hidden leak and a flooring contractor if the subfloor feels soft, since that points to water damage beneath the tile.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.