Reinforced Bitumen Membrane applicators bond layers of felt to a roof to form a watertight covering that will keep the interior of the building dry. Usually several layers are needed although this is not always the case. Bitumen used to be the most popular method for bonding the layers but other methods are now available. It is a skilled job that requires specific training. Safety is also very important, as working at heights and dealing with the different materials involved can be hazardous if the correct procedures are not followed.