Here is some info on tri-coat.......
https://books.google.com/books?id=d6LvAwAAQBAJ&pg=PA938&lpg=PA938&dq=tri+coat,+or+three+stage,&source=bl&ots=IXu8gc3EB8&sig=VF_Zzmpty0TlAD9poPDFl7GXOL8&hl=en&sa=X&ei=VBECVa6bHcaeyAS7iIHwDA&ved=0CEsQ6AEwDA#v=onepage&q=tri%20coat%2C%20or%20three%20stage%2C&f=false