Cellulose ethers, wherein at least a part of the hydroxyl groups of the cellulose backbone are substituted by methoxy groups and hydroxyalkoxy groups, and optionally alkoxy groups being different from methoxy groups, having an unconventional distribution of methoxy substituents at the 2-, 3- and 6-positions of the anhydroglucose units are described. Such cellulose ethers exhibit significantly higher thermoreversible gel strengths than any known hydroxyalkyl methyl celluloses of comparable viscosity and kind and level of substitution rendering them useful as additives for building compositions such as cement based tile adhesives. In particular, such cellulose ethers can be used to improve the attainable adhesion strength after heat storage conditioning and the temporal setting characteristics of a building composition.