reason: the reason for moisture regain is not water leakage, so you can't solve the problem by adding waterproof layer. The real reason is that there is no insulation layer on the wall, which is the case in old houses. In winter, the inner side of the outer wall is high in indoor humidity, and the indoor water vapor naturally condenses on the wall when it reaches the dew point, so it will regain moisture every year, penetrate the cold and sometimes hang frost.

solution: because it is an old house, we have to do a layer of insulation indoors, because it is best to do it on the outer wall, but your house won't work. Insulation such as EPS or insulation mortar can be used in the interior wall, so I won't write down the specific methods, which will solve most problems and can't be solved 1%, because this is a common problem of old buildings.