A mixture composition of a cellulose ether made from raw cotton linters and at least one additive is used in a dry cement based plaster (or render) composition wherein the amount of the cellulose ether in the render composition is significantly reduced. When this render composition is mixed with water and applied to a substrate, the water retention and thickening and/or sag resistance of the wet plaster are comparable or improved as compared to when using conventional similar cellulose ethers.