The fundamental solution is to solve the problem of damp wall. Don't paint the primer until the wall is dry. Both of them are fine.
Because the insulation of the corner of the house was not handled well when it was being built, and it was the top floor, the temperature of the corner was low. However, after heating in winter, the indoor hot water and steam will condense in the corner when it is cold (if the window is not opened in winter, the steam can't get out), and it will be moldy and hairy for a long time. The white we are using now belongs to inorganic substances, and it will become moldy when it gets wet. I have used exterior wall and mildew-proof and waterproof latex paint, but it can only be used for about 2 months. The effect is not obvious, and comprehensive treatment is needed. It is suggested to try a few things: 1. For those who have not brushed latex paint, it is suggested to scrape off the corners of the shed roof (as large as possible) and seal it with waterproof agent. R putty (or real waterproof putty) should be used instead of white. Waterproof primer should be used. 2. Moldy houses can be painted with mildew-proof and waterproof latex paint. If it's troublesome, the easiest thing is. Brush gently with bleach and the musty smell will disappear immediately. Then dry it with a clean rag. One winter only takes 2-3 times to pass, and it will happen again the next year. The best way is to keep warm with extruded board once and for all. Friends who are decorating can consider making a shape in the corner (with extruded board to isolate the wall inside), so that the external wall insulation will not happen.