Abstract: A composition including exfoliated vermiculite and ash produces a soft clinker deposit. In a method to remove ash deposits from furnace structures, vermiculite is added to the gases and ash produced during a combustion process and combines with the ash forming deposits. The vermiculite-ash deposit is softer than a pure ash deposit and can be removed by the application of jets of steam to the furnace structures. An apparatus, used to preheat and inject vermiculite into furnace structures, includes a housing having walls defining a passage. The housing has a distal portion for projecting into containment vessel holding combustion gases and a proximal portion for receiving hot gas under pressure. The passage within the proximal portion includes a narrow section, a tapered section and a wide section.