What the meters show
Why Dry to the Touch Does Not Mean Dry
Here is a call the dispatch desk gets every week: a leak was fixed, the wall looks fine, but a tech puts a meter on it and it reads high. Painted drywall dries at the face while the gypsum core and the stud behind it stay wet. Seal it up or push furniture against it, and mold can grow out of sight for weeks.
The drying target comes from what techs call the dry standard: readings taken on unaffected drywall, framing or flooring elsewhere in the house. 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. After a slow leak under a sink or dishwasher, the bottom of the boards takes on water and swells, so the edges rise and the floor cups. Sanding it flat too soon leaves the floor crowned once it finishes drying. Drying mats and patient monitoring often let the boards settle back down.
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
- Moisture moves from high vapor pressure in wet materials toward lower pressure in drier air
- Dew point tells the tech where condensation could form on cold slabs and outside walls