Preparation Surface preparation is the most critical step in a thermal spraying operation. Coating adhesion quality is directly related to the cleanliness and roughness of the substrate surface. The coating material and the substrate type are the major factors in determining what surface preparation is necessary to achieve consistent bonding. Sprayed deposits do not add to the strength of the substrate. The purposes of surface roughening are as follows: provide compressive surface stresses provide interlocking laminations (layers) increase the bond area decontamination of the surface Parallel stresses on smooth substrate Internal stresses from shrinkage develop in coatings and these stresses increase with increased coating thickness. The stresses are more severe in hard metals or ceramics. Roughening is a method of reducing these stresses by dividing the internal stresses into smaller components which will cancel each other out. As the layers are folded up and down, the coating strength is improved. Stresses over roughened surface tend to cancel