1. It is customary not to do מלאכה ,work or business on Tishah B’Av, so as not to be diverted from mourning. This prohibition is in force from the evening of Tishah B’Av and the entire day of Tishah B’Av. 

2. If a financial loss will be suffered it is permissible to work.

3. Work can be done by a non-Jew, however not in public.

4. Even one who is permitted to work has to be careful not to divert his mind from mourning. One who totally engages oneself in work will not see a blessing from such work or business.

5. Similarly, it is customary that preparations for the meal following the fast should not be done until after חצות.