As has been mentioned before on this forum Ben,the correct mixing of mortar is a skill, which the mix and consitency of the mortar will vary according to the job.Just making mortar "wetter"will not make a good mortar for building bricks/blocks or rendering.It needs a PLASTICISER added to the water."Febmix" springs to mind.This product not only cuts down on the amount of water needed,but more importantly,it adds "microscopic air bubbles"into the mortar,and makes it "buttery".The term "beat it up" means just that.If using a cement mixer to make a batch of mortar,(the best way to mix) the blades and the rotation of the drum,with plasticiser added to the water,will put air into the mix as it turns and throws the mortar around.If you are mixing by hand,then to get a good "airy buttery"mix,you have to work the shovel very hard,turning the mix over,cut the back of the shovel through the mix,lift it up,turn it over again and again,(you're trying to copy what the mixer is doing),as Noseall said, "beat it up."It takes a long time.I've never used a paddle mixer/drill at 500 rpm's to mix mortar,so I can't comment on the result,but you can overmix mortar. I think if you use a plasticiser in the water and a paddle mixer/drill at 500rpm's, that will overmix it and turn it into a whipped up froth,(overmixed,IMO) which would be of little use.For the best results,I would use a cement mixer, or mix well and work it hard by shovel, on a board or in a wheel-barrow.
Roughcaster.