This video is really good to watch if you are studying about American Revolution.
"When a person is tarred, the tar is like hot oil. The tar burns a man's cloth on to his skin. When you peel the tar off, you peel the skin away. There is also a risk of infection when the skin is peeled."
Tarring and Feathering was a punishment. Patriots used it against British officials and loyalists in the American colonies. Tar could easily be found in the shipyards and everyone had feathers in their pillows. Though the tarring was not usually fatal, it was extremely unpleasant. Applying the burning hot tar to bare skin usually caused painful blistering and efforts to remove it often made the condition worse.
Click this link for The American Revolution Timeline: http://www.timetoast.com/timelines/the-american-revolution-timeline--24