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