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. 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. 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. 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 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
- 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 is where the air would condense on a cold surface, which matters on slabs and exterior walls