Is there such a thing like a fuse but for moisture? Some material or dye that can be used to know if a wall or floor is starting to accumulate moisture long before mold appears?

We had a moldy, moist wall, which we had to strip of insulation and dry. There were some issues on the roof (broken roof tile, old chimney) that could have been the cause. The wall is on the first floor, and the mold was growing near the ceiling.

The issues have been fixed. It is not clear where the moisture came from other then 'above' so there is no definitive proof that we have fixed our problems.

But we would like to insulate and plaster the wall again, and start using the room again. It would be nice to know sooner rather then later next time there is some problem on the roof.

This is a related question: monitor-in-wall-moisture, but it seems to attract answers involving active, automatic monitoring.

  • 1
    Perhaps this, but perhaps not. en.wikipedia.org/wiki/Humidity_indicator_card
    – Ecnerwal
    Jul 14, 2023 at 13:45
  • Wall is...concrete?
    – Huesmann
    Jul 14, 2023 at 14:00
  • @Huesmann it's some kind of large porous dark grey bricks covered with some kind of plaster. It was build in the fifties.
    – Ivana
    Jul 17, 2023 at 13:43
  • @Ecnerwal Something like that yes, but suitable to measure humidity inside a living space, so non toxic and reacting to humidity over 50% or 60%.
    – Ivana
    Jul 17, 2023 at 13:44
  • @Ivana sounds like concrete block. Is this a basement wall, or is there no soil on the outside?
    – Huesmann
    Jul 18, 2023 at 12:05

1 Answer 1


There are certainly air humidity sensors, which might serve as a proxy for wall moisture.

There are water sensors which detect leaks onto a surface such as floor, though I don't think any of them are sensitive enough to measure moisture content of concrete until the surface is actually wet.

Both of those are available in home-automation versions for remote monitoring and triggering actions.

There are also moisture sensors used for construction and woodworking which do probe into a surface. But they're relatively expensive, and I don't know of one intended to be read remotely. And they're local; if just one area is starting to leak, a probe elsewhere won't tell you that.

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