Agglomeration due to the sulfation process itself occurs in CFBC boilers firing high-sulfur fuels such as petroleum coke. This study examines the effect of CaSO4, the effect of limestone reactivity, and the potential effect of reactivation on strength development in such deposits. A very unreactive crystalline limestone showed a lower sulfation level over longer times (days to weeks), but the extent of sulfation did not correlate to strength development. This work also shows that CaSO4 by itself cannot produce significant strength development in the ash samples. Finally, reactivation by hydration did not contribute to strength development under the conditions of this study.