Good work, but both can be improved by one builder:
Mayhem 1 can be done with 23 builders (+ 1 floater). I've included a screenshot to show where all the builders are placed, as well as a replay.
I've also improved Mayhem 8 to 3 builders (+ 1 digger), by taking advantage of some walker physics. In the attached screenshot, there's no terrain at the digger's position, so if you turn it into a blocker, it becomes a walker. Then, thanks to the quirky walker physics, it advances forwards instead of falling through the hole. Getting to this position in the first place isn't trivial, but hopefully the screenshot gives you enough of a clue.