There is a portion of drywall to the side of a window in my bedroom (4' W x 5' H) that was saturated with moisture (my pinless moisture meter calibrated for drywall would read 100%). Not sure when the moisture started as the wall does not look discolored, does not feel soft or moist to touch (I've only discovered because I bought a moisture meter). I've had a water mitigation company out, who recommended I get some dehumidifiers and fans and dry out the wall. Rented 19G/day dehumidifier, ran for 4 days, was able to drop all moisture to 0% except for a small 2" x 4" spot by the window to 15%.
Since then moisture in a 0.5'W x 1.5'H area by the window had been fluctuating: raising during the day, and falling during the night. I measured at 9 pm and 8 am. Went from 20% evening 15 % morning to 30% evening 18% morning, and now 70% evening 30% morning. Air humidity in the house is 65% (San Diego), all windows are always open and house is well ventilated.
I'll give water mitigation company a call for advice on next steps, but would like to understand this better myself and get a second pair of eyes.
What would cause the moisture to increase during the day and drop at night? Feels counterintuitive. It hasn't rained in a few weeks.
Is this something I can solve by just dehumidifying longer? Should I let it be? Should I cut out a piece of drywall and see if anything inside needs drying?
Exterior is stucco, there are some visible hairline cracks a few inches above where the moisture is. I have stucco contractors scheduled to patch that out in a few months. We haven't had heavy rains in ~5 months (San Diego).
There are no leaks in the house, had plumber out.
House is on the raised foundation. There was some clean standing water in crawlspace and mud, possibly from the rain or ground water rising up. I've had the water pumped and mud mixed with absorbent sand to be taken out. Neighbors say water table is pretty high and they all had similar issue, I'll grade the dirt in the crawlspace and put up a sump pump.
House is built in 1927, but well maintained overall, framing is redwood.