Last week I think I got a better idea about what is meant by "working a mizzou slurry into the blanket." In any case, so far it looks like I've found a way to handle it that is reasonably simple and effective. Here is what I have so far:
This is the fourth of these letterbox pieces that I've made and the first I've gotten off the form without breaking it. It's still damp and unfired, but okay for gentle handling off of this form:
The polyethylene sheet is taped onto the bottom of the form, so anything on the sheet can be rolled up and wrapped around between layers. I used a strip of duct tape to mark an appropriate position for the blanket and applied the mizzou. The procedure for that was straightforward:
1) Scoop up a cup or two of mizzou from the bag and pour it into a large mixing bowl.
2) Add water, mixing by hand, until soupy. Don't bother with gloves if your skin isn't delicate. It's just mud, more or less.
3) Scoop up a handful and smear it on the blanket. The blanket soaks up excess liquid, carrying fine particles and whatever is soluble. Further smearing turns into rubbing, which dislodges the larger solid bits, which can be brushed off to the side. Second scoops from the same mix have a higher proportion of finer particles, so this can be used fill divots and low spots. After the second scoop, it's time to add more mizzou and water as necessary. Keep at it until the coverage is as thick and uniform as seems reasonable.
Then I rolled the coated blanket up snugly. I think this stuff is 3 mil, and it was adequate for the load, but thicker would be better. The mizzou doesn't adhere to it.
After 22 hrs, it had set up enough to unwrap. I used a cast saw to trim some excess on one side and square up the edges a bit. I expect it to become stiffer and less fragile as it air dries. Tomorrow I will bake it.