The Talmud says, “Where it is the custom to do work on the ninth of Av, one may work; where it is the custom not to do work, one may not do work.” However, whoever does work on the Ninth of Av will not see a sign of blessing from that work.
When the month of Av arrives, rejoicing should be minimized. A Jew must therefore avoid undertaking construction projects from which pleasure will be derived. Also, transactions should be minimized and one must refrain from consuming meat and wine.