Yuck, muck.
Oh boy! Bonsai enthusiasts love muck recipes, so here are a couple more, shared with permission from Florida’s Lakeland Bonsai Society.
If you’re not familiar, muck is used in slab and stone plantings where stronger support is needed, such as vertical swells or edging. It’s a self-adhering clay, like mud, that solidifies some after drying. A good muck is permeable enough for water and roots to penetrate, but solid enough for firm support.
Virginia Boka’s recipe, from Tropical Greensheets:
Combine 1 box of cornstarch and 3 quarts of cold water. Cook this mixture over medium heat, stirring constantly until thick like glue. It can burn the bottom of the pan so be careful. Let it cool to room temperature. Mix together equal parts of soil, peat and chopped sphagnum moss and add this to the cooked starch a little at a time until it is very thick and sticky. Be sure to wear rubber gloves. After experimenting with this recipe, we have found that worm castings work well instead of soil and it seems to help the moss take root faster.
From the Bonsai Society of Brevard:
Mix one part Bentonite with 5 parts Black Kow [a popular brand of composted manure], and one part sphagnum moss cut into one inch lengths (be sure to add the moss before any water is added to the mixture). Add water. The resulting mixture is still sufficiently sticky, easy to handle, stays in place, is very easy to rewet if it dries out, and can be reshaped on the slab as long as it is moist. Wear gloves.
Happy mucking!
Mohawk Hudson Bonsai Society 
WTF!!! What style is this plant being trained into? Why is this guy using wire curtets to remove the extra trunk material? Concave branch curtets, buddy! If I am not mistaken, he just repotted that plant. He should let that plant root in a season or two before trying to fine tune the shape. Trying to achieve the finished image in bonsai in one growing season is like trying to paint a house on a lunch break; poor quality and no long term enjoyment.