Mishnà su Levitico 14:49

Houses become unclean for three weeks and by one of the following three signs: by a greenish color or by a reddish color or by a spreading. "By a greenish color or by a reddish color," in the beginning, at the end of the first week, at the end of the second week, at the end of the third week, or after they have been pronounced clean. "Or by a spreading," at the end of the first week, at the end of the second week, at the end of the third week, or after they have been pronounced clean. They become unclean for three weeks which are nineteen days. None of the leprosy signs is for less than a week or for more than three weeks.

There are ten [laws concerning the negaim in] houses:(1 + If during the first week a nega became faint or disappeared, it must be scraped and is then clean. (3 + If during the second week it became faint or disappeared, it must be scraped and the owner must bring the birds. If it spread during the first week, the stones must be taken out and the wall scraped and plastered, and another week must be allowed. If it then returned the entire house must be pulled down; If it did not return, the birds must be brought. If it remained unchanged during the first week but spread during the second week, the stones must be taken out and the wall scraped and plastered, and another week must be allowed. If it then returned, the house must be pulled down; If it did not return the birds must be brought. If it remained unchanged in both weeks, the stones must be taken out, and the wall scraped and plastered, and a week must be allowed. If it then returned the house must be pulled down; If it did not return, the birds must be brought. If before cleanness was attained through the birds a new nega appeared, the house must be pulled down; But if it appeared after cleanness through the birds had been attained, it must be inspected as if it had appeared for the first time.