One. All he or she has to do is pick up the phone and call the plastering company!
Okay, that may be an overstatement of how hard it can be to work with a subcontractor when they plaster, but it at least makes my point. Plastering is an art. It is physically exhausting, and long winded. Without the right skills and a large enough crew, you will be setting yourself up for failure and frustration.
At a bare minimum, you will need one person to run the mortar mixer all day, one person to transport mud, four people to place mud on the wall and two skilled finishers. Without at least this many people, you will not be able to do the job because the mud will dry faster than you can make it and apply it. To give you an example, when my plaster crew shows up for a job on homes around 2500 square feet, they bring 14 people! Each of these team members has a skill or labor that is required for the company to do the job right.
There are many examples of people plastering their own straw bale home. Some of those homes turn out beautiful while others are obviously plastered by non professionals. The key here is that the first thing people see when they visit your home is the plaster job and the quality of that job will impact the overall beauty of your home. If you believe you have the skills to take on the plastering, then by all means do. the plastering of a bale home is one of if not the biggest expense in the entire project. Your labor will greatly reduce the cost of the home. Be sure to know what your skills are though so that you don’t save money only to end up with an ugly plaster job! As always, I suggest you start small. Check out my DVD on plastering, read books, take a course and then build a small bale structure in your backyard and plaster it. You will know by the end of the project whether plastering is for you.