I bought (2) 20lb. bags of ice and put them into a 5 gallon bucket of water with a mesh bag. That got the water pretty frigid.
As the Castable Refractory was packed into the mold, it remained fairly cool to the touch and quite workable, which allowed us to slow down, focus and pace ourselves during the packing process. The heat from curing didn’t start to several hours later. Using the ice water when mixing the Castable Refractory definitely slowed down the curing process.