hi,i'm going to put up a new fence up soon and have ordered kpost(like postcrete) to fix the concrete posts in.i,m going fairly deep and will need at least 2 bags per post.Ive read you put the water in first and then mix but have also read if you add too much water it can weaken the mix.i'm just wondering how much water do you know is enough to set the post but not too much as to weaken the strength of the mix