The "old trowel saved the job" line is doing a lot of work here. A trowel is a trowel. If the finishers know what they're doing and you got the mud down before it set, the tool is not the story. 400 yards in 104 degree heat is rough, sure, but that's just summer in half the country. Guys pour in that every year. Not saying it wasn't a long day, but one worn out trowel didn't change the outcome. The crew and the timing did.