Grout Problem Diagnoser: What Is Wrong With My Grout?
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Most grout problems have two or three common causes, and a single detail (when it started, where it is, what type of grout) usually separates them. Pick what you see, answer one follow-up question, and the diagnoser points you to the most likely cause and the guide that fixes it.
What do you see?
Three checks before any repair
- Tap the tiles. Drag a coin or screwdriver handle across the tiles around the problem. A hollow sound means the tile has lost its bond, and regrouting alone will not last. See when regrouting won't work.
- Scratch the grout. Drag a key or nail firmly along the joint. Sound cement grout resists and leaves a faint line; grout that gouges or powders is weak through its depth.
- Time the drying. After a shower or mopping, note how long the grout stays dark. A few hours is normal absorption; a day or more points to water trapped below the tile.
Patterns that point to the cause
| Where it shows up | Most likely family of causes |
|---|---|
| Inside corners, along walls, at tubs | Movement: these joints should be sealant, not grout |
| A line across many tiles | Substrate crack or floor deflection telegraphing through |
| Random spots right after install | Mixing, water or finishing technique |
| Low areas of a shower floor | Standing water, drainage, failed pan |
| Traffic lanes | Soil and wear; dirty mop water |
| Exterior or below-grade | Moisture movement: efflorescence, freeze-thaw |
For a full reference of symptoms, causes and tests, see the grout failure diagnostic chart or browse all grout problems.
Frequently asked questions
Can one problem have several causes at once?
Yes. Over-watered grout in a shower with a slow drain can crumble, stay dark and grow mildew at the same time. Fix the cause that started the chain, usually water.
When should I call a professional?
Call one when tiles sound hollow or move, when grout stays wet for days, when there is a leak below, or when cracks run in long lines across a floor. Those are assembly problems, not grout problems.
Sources and standards
- TCNA Handbook for Ceramic, Glass, and Stone Tile Installation, including EJ171 movement joints.
- ANSI A108.10, Installation of Grout in Tilework.
- Manufacturer troubleshooting bulletins and technical data sheets.
Grout Atlas guidance is checked against ANSI A108/A118 and ISO 13007 requirements, the TCNA Handbook and manufacturer technical data sheets. Product formulations change, so confirm details on the current data sheet for the product you buy. Spotted an error? Report a correction.