Cob is a great technology to work with, unhurried. You can’t raise more than about a foot and a half of wall on any given day, because beyond that the self-weight of the mud will make it slump. And then you need at least a day, even under a fierce sun, to dry out the built wall sufficiently for the next build. If you have lot of volunteers however, there are two ways you can go.

TIP!
To speed up work have more than one project going at a time, especially if they are small. When you have raised a wall on one, you can leave it to dry and move to the second location to continue working.

A number of cob block bricks can be moulded in forms [this is actually the adobe route] and sun dried. These can be passed on by a line of volunteers and a greater height can be built in one day.It is useful to have a number of cob blacks handy anyway. There are many places they come in handy, like when fairing a detail, working at a height, making ledges or tiny lintels.

The second option is the one I followed when a group of over ten enthusiastic volunteers showed up one day. I had begun work on both the bath-space and the kitchen. So there was more length of wall to work on in two separate locations.