Can you complete painting the interior of your house during the three weeks/9 days if you started beforehand?
During the three weeks it is permitted, however during the nine days in general it should not be done even if it is only continuing the job. In special circumstances it can be permitted, speak to your local Rov.
M:B 551-12, Kovetz Halachos 5-18 ftnt. 22, KOl Hamisablim Aleho 9-4 ftnt. 23 in the name of R’ Elyashiv zt”l, The Three Weeks pg. 99.