Hello and welcome to JustAnswer!
I'm sorry to hear about your situation and hope I can help.
My goal is to provide you with excellent service today.
The contractor breached the covenant of good faith and fair dealing as well as his other obligations under the contract
by messing up, failing to show up, and not having prepared employees, causing you to go over the allotted amount of time.
Since he has already breached the contract, you would be released from your obligation to provide him with the full 50% that he is due. However, since he (or his employees) did continue to work for you after the mess up, believing that they would receive compensation for what they were doing, you would be required to pay the contractor the fair value for the services that were provided. (This is from the doctrine of promissory estoppal).
To avoid litigation
, I would suggest that you try to reach an arrangement with the contractor to compensate him for the value of the services provided, since he failed to fulfill his contractual obligations to you under the contract itself, but his employees still assisted you and your laborers in finishing the job.
I would say that a fair amount would be the original amount less the value of your and the labor's time spent in fixing the mess and helping get the job done. (If that's 50% or less of the value of the contract, you would have no further obligations under the agreement).
I hope the above information is helpful.
Please let me know if you have any follow up or clarifying questions as I want to ensure that you are completely satisfied with my service.
If not, please remember to rate my answer positively so I get paid for my work.
Thanks and best of luck!