The rain stopped at 9 a.m. By 10 the sun is out, the driveway is drying, and the customer is asking why the crew is still sitting in the truck. The painters are right to wait. The sky dries out long before the siding does.
Why siding lags the sky
Rain soaks into more than the surface.
- Wood absorbs water at the end grain, in cracks, and through failing paint. Beads on top can be gone in an hour while the board underneath is still wet.
- Lap siding holds water in the laps and at the bottom edges, where it drains slowly.
- Masonry and stucco soak up water and release it over hours or days.
- Shade stops the drying. In fall, with the sun low, north and west walls can stay wet into the afternoon while the south side is ready by mid-morning.
We’ve covered which trades go back first after rain. Painting is usually near the end of that list.
The moisture meter settles it
For wood, many paint manufacturers look for a moisture content around 15% or less, and some are stricter. A pin-type moisture meter costs less than one failed job and turns “looks dry” into a reading. Check the places that dry last:
- the bottom edges of lap boards,
- shaded walls,
- trim at joints and corners,
- anywhere near gutters and downspouts.
Painting over damp wood traps moisture behind the film. When the sun heats the wall, that moisture pushes outward, and the result is blistering and peeling.
The rain after matters too
The wait after rain is half the problem. The other half is what comes next. Fresh latex needs time before rain can’t hurt it, and cool fall conditions stretch that time. So a mid-afternoon shower in the forecast can rule out painting that morning, not because the siding is wet but because the new coat won’t be ready for it. Dew in the evening works the same way, and so does a cold night, which we covered in our fall painting cutoff post.
Back and forward at once
DecideWeather’s Painting operation looks both ways around the paint hour:
- Behind: 0.10 inches of rain in the past three hours is a Stop, and any rain at all closes the hour. After rain ends, the Stop holds for two consecutive dry hours before it releases, so the recommendation doesn’t reopen the moment the sky clears. A lighter 0.05 inches over the past eight hours is a Caution, because siding holds on to it.
- Ahead: any rain in the next two hours is a Stop for a fresh coat. So is 0.05 inches or more in hours two to four, or half an inch or more in hours four to six.
When rain is in the window, the recommendation says when it arrives, as a clock time, so the crew knows whether it’s a morning or an afternoon problem. The app reads the sky, though. The moisture meter still has to read the wall.