Hydroxypropyl methylcellulose (HPMC) is a non-ionic cellulose ether made from natural polymer material cellulose through a series of chemical processes. Hydroxypropylmethylcellulose (HPMC) is an odorless, tasteless, non-toxic white powder that can be dissolved in cold water to form a transparent viscous solution. It has the properties of thickening, binding, dispersing, emulsifying, film-forming, suspending, adsorbing, gelling, surface active, maintaining moisture and protecting colloid. In mortar, an important function of hydroxypropyl methylcellulose is water retention, which is the ability of mortar to retain water.
1. The importance of water retention for mortar
Mortar with poor water retention is easy to bleed and segregate during transportation and storage, that is, water floats on the top, sand and cement sink below, and must be re-stirred before use. Mortar with poor water retention, in the process of smearing, as long as the ready-mixed mortar is in contact with the block or base, the ready-mixed mortar will be absorbed by water, and at the same time, the outer surface of the mortar will evaporate water into the atmosphere, resulting in the loss of water of the mortar. Insufficient water will affect the further hydration of cement and affect the normal development of mortar strength, resulting in lower strength, especially the interface strength between the hardened mortar and the base layer, resulting in cracking and falling off of the mortar.
2. The traditional method of improving the water retention of mortar
The traditional solution is to water the base, but it is impossible to ensure that the base is evenly moistened. The ideal hydration goal of cement mortar on the base is: the cement hydration product penetrates into the base along with the process of the base absorbing water, forming an effective “key connection” with the base, so as to achieve the required bond strength. Watering directly on the surface of the base will cause serious dispersion in the water absorption of the base due to differences in temperature, watering time, and watering uniformity. The base has less water absorption and will continue to absorb the water in the mortar. Before the cement hydration proceeds, the water is absorbed, which affects the penetration of cement hydration and hydration products into the matrix; the base has a large water absorption, and the water in the mortar flows to the base. The medium migration speed is slow, and even a water-rich layer is formed between the mortar and the matrix, which also affects the bond strength. Therefore, using the common base watering method will not only fail to effectively solve the problem of high water absorption of the wall base, but will affect the bonding strength between the mortar and the base, resulting in hollowing and cracking.
3. Efficient water retention
(1) The excellent water retention performance makes the mortar open for a longer time, and has the advantages of large-area construction, long service life in the barrel, and batch mixing and batch use.
(2) Good water retention performance makes the cement in the mortar fully hydrated, effectively improving the bonding performance of the mortar.
(3) Mortar has excellent water retention performance, which makes the mortar less prone to segregation and bleeding, which improves the workability and constructability of the mortar.
Post time: Mar-20-2023