What the meters show
Dry to the Touch Is Not Dry
A familiar story: the leak is repaired and the wall looks normal, yet the meter tells a different tale. Drywall paint dries on the surface first and seals moisture inside the gypsum core and the stud behind it. Close that up or hang a picture on it and you can end up with mold you will not see for weeks.
Drying techs set goals by reading the same material in a part of the house the water never touched. When the wet wall reads within range of that dry standard, it is dry; until then, the equipment keeps running.
Wood floors make the point just as clearly. With a slow leak under a dishwasher, the underside of the boards swells and the edges lift, which is called cupping. Sand it flat too early and it crowns once it dries. Drying mats and steady monitoring can often bring the boards back flat.
The physics in plain words: warm, dry air pulls moisture out of wet materials, and dehumidifiers pull it out of the air. Air movers keep the surface boundary layer moving so evaporation does not stall.
- Relative humidity tells you how saturated the air is at its current temperature
- Grains per pound (GPP) measures how much water is actually in the air, regardless of temperature
- Moisture moves from high vapor pressure in wet materials toward lower pressure in drier air
- Dew point is where the air would condense on a cold surface, which matters on slabs and exterior walls