Dry mixed mortar is pre-configured by professional manufacturers in accordance with the national standard "Ready-mixed mortar" GB/T 25181~2010 standard definition, has certain specific use functions, and can be used directly on the construction site of building mortar. It is a construction engineering material composed of ordinary Portland cement, sand, mineral admixture and water-retaining thickening material. The high-quality mortar must meet the national requirements in addition to the indicators, but also should have good construction performance, both must be prepared at the same time.

First, the water-retaining thickening material has a crucial impact on the performance of dry mixed mortar, and the water-retaining thickening material can play a role in the mortar to improve the water retention rate, improve workability, prevent bleeding and stratification.
Second, the mortar should have a certain plasticity, also known as the fullness of the mortar, which can improve the elastic modulus of the mortar, anti-flow hanging and mortar fluidity, thereby reducing the probability of cracking hollow drum.
Third: In order to improve the construction performance, the mortar should have a certain lubricity, which can improve the construction efficiency.
Fourth: The construction can make the mortar in the specified time can be pressed, and the construction time of the mortar must be shortened. It can be seen that high-quality mortar must have the above performance indicators, which has positive application significance for dry mixed mortar.

1. Physical properties of water-retaining thickener
After adding water, the dry mixed mortar is divided into bound water, lubricating water and free water. The part of the cement that reacts fast will undergo hydration reaction after adding water, consume part of the water first and cannot escape the mix, and this part of the water is defined as bound water. When water encounters dry water, fine aggregates and mineral materials, etc., the surface of cement, fine aggregates and mineral materials will adsorb part of the water, so that the dry material is wet and cannot escape the mix, but it can be replaced by water in nearby parts, which is defined as wet water. The excess water of the mortar is free water, which plays a lubricating role in the mortar, and the fluidity and lubrication effect of the mortar largely depend on the amount of free water. Therefore, the water retention rate of mortar must meet the needs of the wall base surface adsorption, mortar maintenance and water loss due to weather and other factors. Therefore, the water retention rate of mortar is very key, that is, the free water is retained in the mortar to ensure the needs of the mortar hardening and maintenance, and the use of a certain amount of fly ash and ultrafine mineral powder to increase the specific surface area of the material can also play a role in water retention, while increasing the adsorption of water, to minimize the free water.

2. Plasticizing lubrication performance of mortar
The polymer has a strong binding force on the water molecules, and the water is firmly adsorbed, thus reducing the freedom of water. At the same time, small bubbles are generated in the mortar, which on the one hand can play a good lubrication effect and improve the fluidity and anti-flow of the mortar. On the other hand, it can also suspend the aggregate and reduce the subsidence of the aggregate, so that the mortar has a good plasticizing effect, also known as the mortar fullness, which is also an important indicator to improve the construction performance of the mortar.

3, shorten the construction time
Water retention in mortar is important, but it will prolong the construction time of mortar, thereby affecting the construction efficiency, and will cause the shrinkage rate to increase, so reduce the amount of water added, and correspondingly reduce the amount of free water, so as to improve the quality of mortar and shorten the construction time to increase the construction efficiency of workers.

4, the influence of the water retention rate on the mortar
The water retention rate of mortar is a very important index, and the water retention rate will directly affect the shrinkage, bond strength and construction performance of mortar.

① It will cause plastic cracking: the water retention rate of the mortar is poor, and the water will be easy to disperse, especially for the air block wall with fast water absorption, the water is sucked away by the substrate, and the mortar is not condensed, and it is not able to resist the tensile stress caused by the volume contraction, and the mortar has irregular cracks.

2 will cause hollow drum: mortar bleeding will cause uneven mortar components, resulting in a decline in the overall performance of mortar, for masonry, plastering mortar bleeding, water loss is fast, easy to be taken away by the substrate, cement hydration is insufficient, reducing the mortar and substrate bonding force. Under the change of temperature and humidity, the mortar produces volume deformation, forming stress, resulting in the separation of the mortar and the substrate. This phenomenon is the main cause of the hollow drum of mortar.

(3) will reduce the constructability: the mortar water retention rate is poor, there will be mortar bleeding, mortar after water mixing transport process or placement will occur stratification and upper, middle and bottom consistency is different, resulting in poor cohesion, plastering easy to fall ash, mortar poor operability and other consequences.

To sum up, while controlling the quality of raw materials, mortar additives with good quality and full functions should also be selected to make up for the deficiencies in the function of mortar, so as to enhance the workability and adhesion of mortar, improve the crack resistance of mortar, reduce permeability, make mortar not easy to separate by water, meet the national performance indicators and construction performance indicators of mortar, and ensure the quality of mortar.