Numbers tell the tale
To measure the present moisture in walls and floors a reliable moisture meter is necessary. A moisture meter with two pins is pushed into wood or other soft materials so the electric resistance can be measured. The same can be done with an analogue or digital Ohm meter. On hard surfaces like bricks, tiles, joints, concrete, natural stone, ... this doesn't or barely works. The pins cannot be pushed into the material. There are other devices on the market for there materials.
To measure and find moisture in construction materials, the surface can be scanned high frequently to a depth of approximately 12cm.
This gives an indicative value with what cam be compared with if a certain construction material is wet, moist are dry and in what quantity. Increasing numbers can indicate a direction.
With such a high frequential field scanning device you can measure among others which brick holds water and which doesn't. With this, a certain diagnosis can be confirmed or denied.