Rambam - 1 Chapter a Day

There is an isolation period of three weeks, i.e., nineteen days, for blemishes on houses. For the seventh day counts for the first and the second week and the thirteenth day counts for the second and the third week. Thus if three weeks are necessary, an inspection is made on the seventh day, the thirteenth day, and the nineteenth day. The isolation of a house for three weeks is not explicitly mentioned in the Torah. Similarly, most of the laws applying to blemishes on houses were conveyed by the Oral Tradition.

The explicit laws pertaining to them that are stated in the Torah and the Received Tradition are as follows: When a priest comes to see a intense green or intense red blemish that is sunk beneath the surface on the wall of a dwelling, as we explained, he should isolate the house for seven days. Even if at the outset, it was entirely intense green or intense red, he should isolate it. On the seventh day, he should inspect it. If the blemish faded or, needless to say, if it disappeared, he should scrape away the place of the blemish and the house is deemed pure.

If its color remained, but it did not spread, it should be isolated for another week and inspected on the thirteenth day. If it faded or, needless to say, if it disappeared, he should scrape away the place of the blemish and purify the house with fowl.

If, at the end of the second week, he discovered that the blemish had spread or retained its color, he should remove the stones on which the blemish had been manifest, scrape off the mortar that had supported them and deposit it outside the city. He should plaster the entire house and isolate it for a third week.

On the nineteenth day, he should inspect it. If the blemish returned and comprised two grisim, this is considered to be spreading after plastering and the entire house should be destroyed. If the blemish did not return, he should purify the house with fowl. If, however, at any time before it is purified with fowl, the blemish returns, the house should be destroyed. If another blemish appears in the house after it was purified, it should be inspected as if for the first time.

Similarly, if the blemish spread at the end of the first week, he should remove the stones on which the blemish had been manifest, scrape off the mortar that had supported them and deposit it outside the city. He should plaster the entire house and isolate it for a second week. Afterwards, he should inspect it. If the blemish returned and comprised two grisim, this is considered to be spreading after plastering and the entire house should be destroyed. If the blemish did not return, he should purify the house with fowl. If, however, at any time before it is purified with fowl, the blemish returns, the house should be destroyed. If another blemish appears in the house after it was purified, it should be inspected as if for the first time.

When the priest removes the stones on which the blemish was found, he should not remove less than two stones. He may not take stones from one side of the house and bring them to the other, for Leviticus 14:42 states: "And they shall take other stones." Similarly, he may not take mortar from one side of the house and bring it to the other, for that verse states: "And he shall take other mortar and plaster the house."

He may not plaster the house with lime, only with mortar, for the verse states: "And he shall take other mortar." He should not bring one larger stone in place of two that he removed or two smaller stones in place of one that he removed. Instead, he should bring two in place of two. He may, however, bring two in place of three.

If there was a blemish on a wall between one person's house and another's, they both must remove the stones; they both must scrape away the mortar, and they both must bring other stones. The owner of the blemished house alone brings the new mortar, as implied by Leviticus 14:42 which states: "And he shall take other mortar and plaster the house." From the use of a singular form, we learn that his neighbor does not join with him in the plastering.

The following laws apply when there is a blemish on a stone in the corner of a house. When the owner removes the stone, he removes it entirely. If he must destroy the house, he must destroy only his own and leave his neighbor's. There is an unresolved question if the part of the stone that projects into his neighbor's house is considered as a handle to his stone and brings impurity to it.

When a blemish was discovered in a house and there was a loft built over it, the beams of the ceiling should be left for the loft. If it was discovered in the loft, the beams should be left for the house. If there was no loft on top of it, all of its stones, wood, and mortar are destroyed with it. The partitions on the roof and the lattice of the windows may be saved.

When a person takes stones from a house that had been isolated and builds them into a house that is pure, if the blemish returns to the house that had been isolated, he should remove those stones from the pure house. If the blemish appears on the stones that he added, the isolated house should be destroyed and the second house isolated, as is the law with regard to a house on which a blemish is first discovered.

How is a house on which there was a blemish purified after the stones were removed and it was plastered? One should bring "living water" in an earthenware container, two fowl, a cedar branch, a hyssop, a crimson strand, like the purification of a man in every respect. The difference is in the purification process of a man, one sprinkles the blood seven times on the back of the hand of the afflicted person. And in the purification process of a house, one sprinkles the blood seven times on the lintel of the house from the outside. The remainder of the practices are the same.