Water retention additives play an important role in modern building products, particularly in dry-mix mortars [1]. Their function is to prevent uncontrolled water loss into porous substrates such as brick, lime stone, and aerated concrete. In industrial products, cellulose ethers dominate this market because of their favorable cost effectiveness and their good environmental compatibility [2]. The first reports on the preparation of methyl cellulose and its derivates originate from Lilienfeld [3], Leuchs [4] and Dreyfus [5]. Based on their pioneering work in cellulose ether synthesis, production started in Germany in the 1920s and in the United States in 1938. Major current applications of cellulose ethers include wall renders and plasters, joint compounds for gypsum board paneling, cementitious tile adhesives (CTAs), floor screeds, self-leveling underlayments (SLUs) and water-proofing membranes [6]. In dry mortars, cellulose ethers serve to provide water retention and viscosity. Some types retard Portland cement hydration severely [7], [8]. The effect depends on the specific composition (e.g. degree and type of substitution) of the cellulose ether. Application dosages may range between 0.1 and 1.5% by weight of binder, depending on the desired properties. Among the most frequently used cellulose ethers are methyl hydroxyethyl cellulose (MHEC, also referred to as HEMC) and methyl hydroxypropyl cellulose (MHPC) [9], [10], [11]. MHEC is predominantly applied in self-leveling flooring compounds and cementitious tile adhesives (CTAs) while MHPC, because of its air-entraining effect stemming from the hydrophobic hydroxypropyl groups, is the product of choice for wall renders and plasters.