The finishing of a cob pizza oven has two three major roles. The first one is to provide a visually desirable aesthetic touch to the oven. To serve this purpose, the finishing coat is mainly added with iron oxide to provide the bright earth brown red color. The second function of the cob clay finishing is to provide a firm and protective outer covering. To effectively play this role, all the three coatings placed above the insulating material should be mixed with polypropylene fibers. These fibers create a firm coating that can withstand and resists the normally unintended external force.
Lastly, the cob oven finishing plays as a heat barrier. Even though the insulating material traps the majority of heat that would have been lost through the surface, the poor contracting finishing material has a slight role in heat protection.
Further information: Wood Fired Pizza Oven Building Plans and Types of wood fired pizza ovens