In prescription-based specifications the engineer will typically set out in detail all requirements for the materials and shotcrete mixture proportioning as well as the type of equipment required for batching, mixing, supply, and application of shotcrete. In performance-based specifications the engineer will specify the required performance characteristics for the shotcrete and let the contractor select the materials, mixture proportions, type of equip­ment and application procedures to be used. In general, perfor­mance-based specifications are preferred to prescription-based specifications in that they encourage innovation and introduction of new technology and generally result in lowest cost to the owner. Let us examine in some detail the differences