Contractor Running Very Behind Schedule. What would you do?

[Bill Goodland]

So I purchased a new primary residence that will be either a future flip or rental. As my business grows, I am trying to hire out more work so I have a contractor that a lot of the local flippers I know use. I've seen his work before and he gave me a reasonable bid to do an entire house rehab of mostly paint, flooring and light fixtures. It's now 3 weeks into the contracted start date and as far as I know, only demo of the floors has been completed and this was scheduled to be a 4 week job. I haven't given him any money yet and I'm trying to be understanding and follow up with him multiple times per week and get a different excuse with the story of "I'm actually heading over there today and my guys will be getting XYZ done". I haven't gotten any updates and have explained that I need better communication to not much avail. Trying to balance between stern and not getting taken advantage of with being understanding and not trying to burn a bridge of a relationship with a contractor I planned to use for future rehabs because I have been impressed with his quality of work and price before. Does that mean I need to sacrifice timeline? I know this is an issue every rehabber faces so I'd appreciate any thoughts on how else to handle this such as specific penalities in the contract because he hasn't even reached the 30% completion threshold that we agreed upon previously in order to get any payment.