We've done that method too Frank. It works great if you aren't going to be "doing" anything with the post for a few days and that's how we always do mailboxes etc. But for fence posts and deck posts we usually need/want to do something with it within 24hrs that's when we do the "Assembly Line" method mentioned above and add water. I just HATE mixing it in a bucket/barrel/wheel barrow and then trying to maneuver it into a hole. We just dump, pour, agitate and go to the next.
Allen
