Notes from the drying techs
Dry to the Touch Is Not 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. 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.
The drying target comes from what techs call the dry standard: readings taken on unaffected drywall, framing or flooring elsewhere in the house. When the wet wall reads within range of that dry standard, it is dry; until then, the equipment keeps running.
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. Sand it flat too early and it crowns once it dries. 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 is how full the air is relative to what it can hold at that 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 is where the air would condense on a cold surface, which matters on slabs and exterior walls