Pay your contractor on an incentive/penalty basis?

[Ryan Dossey]

We have a particular contractor we have used for 2 jobs now. They do GREAT work. They are creative and stick to budget. But they are slow. I think I want to give them one more shot. Here are my thoughts.  

Offer something like an extra grand for deadlines being met. When I set up the scope of work I'm going to ask them to date when each phase of the project should be completed. I'm thinking for any deadline that's missed they forfeit a certain $ amount. 

What do you guys think?