MRROOFER.......It is unfortunate that this has happen to you, It is like raising your children! (no matter how you raise them, it is a crapshoot on how they will turn out!). Same goes with trying to hire the right crew, what looks to be great...is not always what it seems.
I have a motto in roofing and it goes like this***..."When my only solutions are negative...I pick the best of the worse!"***
1. You could fire all the employees...and start anew
2. Continue business as usual, hire a QC manger (if you company is big enough and revenues allows for it)
3. Change all pay to piece rate (Crews may get fed up and hold you hostage...IE...threaten to quit forcing you to hire new crews)
With all of these issues facing you...there is a compromise and can work to your advantage...to a point
A. Pay your guys hourly for the tear-off phase only: This is the best solution because every tear-off (steep/extra layers/woodwork/change orders) is different.
*** (When you have change orders during the tear-off process.....don't pay piece or add additional hours to their pay...pay them as part of the tear-off.)***
B. After the tear-off phase is complete, then switch them to piece work and pay them the rate for your market.
**How does this benefit you??? **
-Guys want to make as much money for as little time as possible...but if you are paying them hourly for the whole day...they will bring their milk and cookies to work with them
-Yes...you will get some milking of the clock (but that is a part of a negetive that has been reduced)
-The install (once every thing is prepped) will take only a couple of hours to complete...they go home early with good pay and and you completed job.
I have conducted monetary evaluations and comparisons of piece vs hourly work on many projects.....the one thing that sticks out...is that the system described above saves you small amount of labor dollars on eash job....over 100 projects...that small amount accumulates to save you alot.