We have a pretty poorly designed mash tun/stripping still so we can only do step down mashing. We heat the water to the max temp we are using, add a high temp enzyme to the water and then add the milled grains at the temps we are mashing them in. It generally works OK for us. We do get some clumping on the surface of the mash due to the design of our equipment and we used to use a paddle to deal with that. A couple years back we added an electric grout/mortar mixer which works well to break up the clumps on the surface. Our mashing vessel stirs the mash and we hold the mortar mixer through the manhole and let it rip, it chews up the clumps on the surface and they get mixed in. Its not perfect, we'll run the mortar mixer for a few minutes, close the manhole and let is continue to mix for awhile, repeat as necessary until everything is smooth. The mortar mixer is a lot easier than the paddle was.