Thought the old timer was messing with me about watering the subgrade, he wasn't
Last Tuesday we were pouring a 40x60 slab out in Mesa and this older finisher kept telling me to hose down the gravel before we laid the vapor barrier. I figured he was just bored and wanted to slow us down, since dry dirt and wet dirt both look the same to me under plastic. He grabbed the hose himself, soaked it down, and told me if I skipped it the mix would pull water out of the ground and set up crusty on me. Sure enough the truck showed up an hour later and the pour flowed way smoother than the last one we did on dry base, zero honeycomb on the edges. Anybody else's old guys swear by this or is it just a desert thing?
Kept a jug of water and a garden sprayer on the truck for years because of this exact thing. On a hot day that gravel sucks the water right out of the bottom of your mix and you get a crust before you even get the bull float out. I spray till it's damp but not standing in puddles, then roll the barrier out right after. One thing to watch is you don't want it soupy, or you'll be fighting ruts when the chute guy walks the base. Old timers earn their keep one pour at a time, sounds like yours saved you a bad day.