Notes from the drying techs
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. 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.
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.
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 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 is how full the air is relative to what it can hold at that 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