Backfill is an important component of many mining operations. Over time, operational changes can deviate from the original design intent of the backfill system. A general understanding of the chemical, physical, and rheological properties of the backfill material, obtained by laboratory testing, may prevent and/or minimize some of the common operational backfill system issues experienced by mining operations. Keeping the backfill system operational is often a shared responsibility between the mill, for the preparation of the material, the geotechnical (rock mechanics group), for determining the backfill strength requirements and the mining department, for planning the underground distribution and placement of the backfill. When changes are made in any of these areas, knowing the properties of the materials in the design may explain how changes to the tailings properties, the strength requirements and/or the underground distribution could affect the operability of the system. While the design of most backfill systems is fairly robust and can accept some variability, this presentation examines the information obtained by laboratory material testing and how it can be used to maintain efficiency in the operability of the backfill system.