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. Seal it up or push furniture against it, and mold can grow out of sight for weeks.
Drying techs set goals by reading the same material in a part of the house the water never touched. Only when the wet material matches that baseline is it considered dry, and not a day before.
Hardwood floors show the same problem in a different way. With a slow leak under a dishwasher, the underside of the boards swells and the edges lift, which is called cupping. Sanding it flat too soon leaves the floor crowned once it finishes drying. Drying mats and steady monitoring can often bring the boards back flat.
The short version: dry, warm air draws water out of materials, dehumidifiers remove it from the air, and air movers sweep the surface so evaporation keeps going.
- Relative humidity tells you how saturated the air is at its current temperature
- GPP is the actual weight of water vapor in the air, which is the number techs track day to day
- Vapor pressure moves moisture from wetter materials toward drier air
- Dew point tells the tech where condensation could form on cold slabs and outside walls