In order to control the ash deposition, a surface treatment of the tubes, using a thermal spraying technique, was proposed in this study. First, adhesion forces between ash pellets and several alloy specimens were measured. using a tensile testing machine, to evaluate validity of this technique for a long period. The result shows that a Ni alloy as the thermal spraying material could reduce the adhesion force. Second, the reduction mechanisms of ash deposition were elucidated. observing the interfaces between the ash pellets and the alloy specimens by a scanning election microscope with energy dispersive spectroscopy. As a result, diffusion of Fe compounds in the tube could be depressed by the Ni alloy coated on the tube surface. Finally, field tests of this technique were also carried out in some practical multi-fuels fired boilers, so that this technique showed a good performance, especially for clinker. (C) 2011 Elsevier B.V. All rights reserved.