Most, well all of my pipes had some type of pre carb coating inside the bowl. Now, a cake has begun to build up in some of them and I'm wondering, are you supposed to build it or is that the purpose of the pre carb coating? I generally take a paper towel and twist it in the bowl after each smoke which keeps the cake to a minimum. The reason I noticed was I smoked a cheap aro and the next day I did the paper towel thing and it just started gumming up and peeling right off. Never seen that before.