No, but a few factors could affect this decision. Elastaseal is an extremely versatile waterproofing material, which means that in the majority of cases there is no reason for the existing substrate on a leaking roof to be removed. Elastaseal forms an immensely strong bond and will create a waterproof membrane that is elastic (able to withstand movement) and also permeable to vapour, allowing the roof to breathe. Where existing roof materials are to be covered, it is important to ensure the substrate is sound, free from loose material, clean and dry. When carrying our your roof condition survey, your local Area Business Manager will advise on the best course of action and what primers are needed to achieve ideal adhesion levels.