A method using retardant to inhibit solidification of slurried fly ash particles that were collected on a collection surface. The slurried particles are transported in a pipeline to a collection or disposal site during or after the addition of the retardant to the slurry. The retardant can be a dispersant, a deflocculant, a scale inhibitor or a sequestering agent such as a phosphate, organic phosphate, polymer, and mixtures thereof.