Answer:
(i) It is caused by moisture stagnating or accumulating inside the walls due to partial defects on the exterior wall. After the sun shines, this moisture forms water vapor, which during the evaporation process exerts a tremendous amount of pressure (volume expansion 1140 times), enough to destroy the paint adhesion function in the room. This vicious cycle repeats from point to point, and of course, there will be a complete peeling and mold formation.
(ii) In response to this phenomenon, the most commonly used method by renovation and decoration workers is to apply AB glue (which is a type of mortar applied to the surface of the wall cancer to mask the appearance of the wall cancer by increasing the hardness of the AB glue). After this, the surface is repainted with cement; this method can take as little as three months or as long as a year to cause the paint to swell completely, which is equivalent to a poor job done.