Adhesives do not adhere sufficiently to many surfaces. Prerequisite for the adhesive to bond is the complete wetting of the surface by the adhesive. In the case of unprepared surfaces, wetting is almost always disturbed by surface layers formed during storage or pre-treatment. For this reason, cleaning of the surface of separating substances is always required for any type of material, even if there is no visible contamination. Plasma cleaning can remove ultra-fine contaminations even in narrow cracks, undercuts and cavities.