Fly ash adhesion is a universal occurrence in a wide range of combustion plants and causes severe problems that disturb the stable and long-term operation of the facilities, such as decreased heat-transfer efficiency and blocked gas flows. Consequently, controlling fly ash adhesion is a challenge for combustion plants worldwide. Herein, we demonstrate that not only a chemical effect, i.e., changing the composition of fly ash to prevent the formation of eutectic systems with relatively low melting points, but also a porosity effect can be a key enabler for controlling fly ash adhesion at high temperatures. In particular, the addition of fine particles to fly ash powder beds is an effective method for increasing the porosity, which leads to the suppression of tensile strength. (C) 2020 Elsevier B.V. All rights reserved.