Wood absorbs water and swells. Where the moisture sits in the board decides the shape the floor takes, and the shape tells us where the water is.
Never sand a cupped floor until readings show it's dry; sanding too early is what turns cupping into permanent crowning.
| Condition | What it looks like | What it means |
|---|---|---|
| Cupping | Board edges higher than the center | More moisture under the board than on top; water came from below or soaked in |
| Crowning | Center higher than the edges | Often happens when a cupped floor is sanded before it dried |
| Buckling | Boards lifting off the subfloor | Severe swelling; often needs replacement |
| Gapping | Spaces opening between boards | Shrinking as boards dry out, sometimes too fast |
| Dark staining | Black or gray marks at seams | Long exposure or a reaction with the finish or wood |


