When is the right time to hire another contractor to finish the job?

This is it, I’ve had it! This initially-predicted 2-3 month long renovation is now going on 9 months. It took about 4 months to finish 75% of the work, but these last 5 months have been dragging on and on. He only comes when he has time between his other jobs, sometimes he says he will come but he won’t show up and ignores our phone calls and texts. When he DOES come he often needs to re-do a lot of his work because his work is done incorrectly. Now that ‘renovation season’ is upon us I can tell he is getting busier and coming less often. Now that there is about 10% of the work remaining, can we give him a deadline and tell him that if he doesn’t finish the work in a certain time, we will consider hiring someone else to finish the work? We need to communicate to him effectively that we simply cannot wait any more. Any advice you have would be sincerely appreciated. Thanks in advance!!