HPMC in Wet Mortars
JINJI® Hydroxypropyl Methyl Cellulose (HPMC) is a non-ionic cellulose ether polymer based on cellulose, a natural polymer derived from refine cotton linter.
HPMC can improve the cohesion and water retention of the Spray mortar mixture.
Water retention rate is an important performance index of Spray Mortar. While some components of mortar and concrete are the same, they function differently. Generally, concrete is poured in concrete and wood form work that retains most of the water. The mortar is usually used on water-absorbing surfaces, and the moisture in the mortar is easily lost or evaporated into the atmosphere, so the water retention of the mortar becomes more important than that of the concrete.
The reason why HPMC enhances the consistency of spray mortar is water-retaining, can improve the cohesiveness of mortar, reduce the bleeding rate of mortar to a certain extent, but improve the fluidity of spray mortar within a specific dosage range; However, the high content of Hydroxpropyl Methyl Cellulose makes the wet-mix mortar too cohesive, which reduces the fluidity of the mortar and makes the mortar more challenging to construct.
HPMC can increase the tensile bonding strength of wet-mixed mortar.
For plastering mortar, bond strength is an important indicator. Generally speaking, plastering mortar requires good workability. In order to form a uniform mortar layer on the construction surface. The strong bonding strength of the mortar can make the mortar and the base layer firmly bonded, and the long-term use will not cause cracking and falling off.
The cellulose ether and the hydration particles form a thin layer of a polymer film with a sealing effect and preventing water loss, with good water retention, so that it has enough moisture to ensure the hydration and strength development of the cement and improve the bonding strength of the paste. On the other hand, Hydroxpropyl Methyl Cellulose enhances the cohesiveness of the spray mortar to ensure its good plasticity and flexibility, reduces the slip stress between the spray mortar and the substrate specimen interface, and further improves the interface bonding ability of the mortar.
It is recommended that during the preparation process, HPMC is mixed into the spray mortar in the form of a solution rather than directly integrated with the form of a powder.
The former has a better effect on improving water retention, cohesion, and mechanical properties of spray mortar. When the converted content of Hydroxpropyl Methyl Cellulose is in the range of 0.01%~0.04%, the water retention rate of HPMC in solution form is 1.4%~3.0% higher than that of powdered HPMC in spray mortar. Therefore, HPMC mixed in the form of a solution has a better effect on improving the water retention of spray mortar.