Because of legislation and environmental concerns, washing powder manufacturers have phased out phosphate builders in favor of substitutes such as sodium carbonate. This has meant that the new formulations have a greater tendency toward unwanted agglomeration (caking), based on moisture uptake and migration. This study examines the feasibility of using a Freeman FT4 powder rheometer to examine the effect of moisture migration, using the basic flow energy value to compare formulations of sodium carbonate content 27-37% and sodium sulfate content 10-20% by mass after 7 d exposure to 80% relative humidity at 20 degrees C. The results showed that 31 and 33% sodium carbonate formulations were the most resistant to caking, with 27 and 37% being the most susceptible under the test conditions. Using the method of Brockbank et al. (2015), the FT4 was also used to detect the presence of a hard crust; under the test conditions, no hard crust was found. However, the presence of soft caking was detected in the force-height profile, showing a less abrupt transition.