The selection of water-retaining and thickening material should be based on the performance, use conditions and construction requirements of dry-mixed mortar. In general, the water retention of mortar is not the higher the better. If the water retention of mortar is too good, it may lead to the prolonged setting time, crusting and decrease in the compressive strength of mortar. Therefore, each variety of dry-mixed mortar has its own appropriate range of water retention. For example, using the ordinary dry-mixed mortar with 1 thickness of 10-20mm, the water retention should be 88%-92%; using the thin layer dry-mixed mortar with a thickness of 3-5mm, the water retention should be over 95%.
For example, according to masonry block materials, masonry mortar can be divided into sintered common brick, small concrete hollow block, autoclaved lime sand brick, autoclaved fly ash brick and aerated concrete block. Each kind of block material is different in the surface condition, pore structure, the number of pores, and the shape of blocks. Some requires the mortar joint to be 8-12mm, others 3-5mm. For mortar of thick mortar joint, the water retention should not be too high, otherwise, will significantly reduce the compressive strength of mortar, prolong the setting time and affect the normal speed of construction. At this time, mortar thickening powder can be chosen as the water-retaining and thickening material. If the thin layer mortar with a thickness of 3-5mm is used, the requirement for water retention will be very high. At this time, the cellulose ether can be chosen as the water-retaining and thickening material.