The purpose of this thesis is to explore the materials and function of traditional renders applied to earthen buildings, and methods for their conservation. Although this study deals with earthen buildings, their construction techniques and overall deterioration are outside the scope of this study. The mentioned plasters prepared from representative traditional recipes - appended at the end of the study, and found to be used since ancient times in many parts of the world - have been compared through laboratory testing for their most important physical and mechanical characteristics: adhesion to the surface, water vapor permeability, capillarity, and abrasive resistance both in dry and wet conditions. Since there are no recorded standard procedures to evaluate the effectiveness of surface treatments on earthen renders, the experimental tests have been designed based mainly on those of the ASTM (American Society for Testing Materials) and CRATerre (Centre International de la Construction en Terre). In addition, three consolidants, reported in recent conservation literature for the stabilization of porous materials - specially clays - were included in the testing program.