Prescriptive specifications have exact details and instructions, while performance specifications have desired results. Performance specifications offer the supplier or contractor flexibility, while prescriptive specifications do not.

Prescriptive specifications restrict the composition of cement or its constituents by giving chemical or physical requirements or limiting the raw materials used. Performance specifications give performance requirements only. Both ASTM C 150 (for portland cement) and ASTM C 595 (for blended hydraulic cement) have prescriptive elements.

Whilst prescriptive specifications are characterised by detailed descriptions of material and workmanship requirements, performance specifications lay down the desired end results and verification methods. It is often said that the latter allows flexibility and encourages innovations in the use of materials, systems and methods.