Tried adding a splash of water to my mortar mix on a hot day in Tucson and it set up like peanut brittle
I was laying block in 104 degree heat last June and figured a little extra water would keep things workable, but the mortar flashed so fast I had to chip three blocks back out. Cost me about 40 minutes and a half bag of mix, so now I just keep the board shaded and mix smaller batches instead. Anyone else fight with summer mortar or is it just me?
Last July in Phoenix I started dipping my trowel in a bucket of ice water between blocks instead of dumping water in the mix. Keeps the mortar from cooking on the board without messing with the ratio. Also started mixing half batches, like you said, and setting the wheelbarrow in the shade with a wet towel over it. That got me through the whole west wall without losing a single block.