Contemporary requirements for gypsurn-based composite materials (GBCM) for rendering or plastering include controlled setting time, good workability, sag resistance, high compressive and flexural strength, perfect bond to concrete or brick, water resistance, and improved heat and noise insulation. The application of a number of chemical admixtures and mineral additives was found to be necessary to provide the required performance for gypsum-based materials. Among the necessary chemical admixtures are the following: a retarding admixture, a water-soluble polymer (MC), an air-entraining admixture (AE), and a superplasticizer (SP). This paper describes the effect of the different admixtures on the consistency, setting time, and the compressive strength of GBCM. It also discusses the application of the stepwise optimization (SWO) method for the evaluation of the GBCM composition. (C) 2002 Published by Elsevier Science Ltd.