Substances capable of removing dirt, grime or impurities from a surface.  Correct surface cleaning is necessary for optimum bonding and sealing.  Bond strength is determined to a greater extent by the adhesion between the joint surfaces and the adhesive.  It is important to understand that adhesive joints are stronger the more thoroughly the surfaces are cleaned.  The complete removal of oil, grease, dust and other residual dirt from the bond surface is required for the best adhesive joint.