Water retention principle of cellulose in putty and mortar

We all know that the main function of cellulose is water retention and thickening, and the water retention rate is especially important in the application.

The most important main material for putty and mortar is cement, which is a water-hard material and must have enough water to make it harden completely. So sometimes putty on the wall will appear after the situation of powder removal, as well as mortar after hardening will crack, not strong enough, these problems are caused by the cement is not completely hardened. And cellulose water retention in which plays an important role.

So how exactly does cellulose play a water retention effect?

Cellulose dissolved in cement slurry after its unique porous network structure and film-forming properties will form a similar film-like mesh structure, effectively wrapped with the water in the slurry, to prevent the slurry in the water evaporation. From another molecular structure point of view, cellulose ether still maintains the basic skeleton structure of cellulose, both dehydrated glucose ring structure, and calcium ions in the cement to form sugar-calcium molecular compounds, play a role in slowing down the role of cement, thus delaying the hydration of cement. (For example, gypsum-based products will be added to sodium gluconate to slow down the setting) In this two-layer effect, determines the cellulose in the hydration of cement plays an important role.

The water retention rate of cellulose ether also depends on the water absorption of the base, the composition of the mortar, and the thickness of the mortar layer. Some customers’ mortar formulations use low-quality cement and sand with a high ash content, which absorb a lot of water, thus resulting in cement hydration not being supported by sufficient water. Substrates that are not cleaned and not adequately sprayed with water to the substrate prior to construction can also lead to a large amount of water loss in the slurry. Insufficient addition of cellulose is also an important reason for substandard water retention, but the addition of cellulose can not exceed 6 kg per ton, because cellulose and air-entraining function, which will reduce the flexural and compressive strength of cement. Cellulose viscosity is also an important reference index, but the viscosity reaches 100,000, water retention is no longer due to the increase in viscosity and increase. So the selection of cellulose must pay attention to this point, because the viscosity is too large, will cause the effect of sticky knife, affecting the smoothness of construction.

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