Tile adhesive powder and cellulose ether: How do they jointly affect the viscosity and setting time of mortar?

Tile adhesive powder and cellulose ether: How do they jointly affect the viscosity and setting time of mortar?

Tile adhesive is a mixture of cement as the main cementing material, supplemented by graded aggregates, water retaining agents, early strength agents, latex powder and other organic or inorganic admixtures. Usually, it only needs to be mixed with water when used. Compared with ordinary cement mortar, it can greatly improve the bonding strength between the finishing material and the substrate. It has good anti-slip properties and excellent water resistance, heat resistance and freeze-thaw cycle resistance. It is mainly used to paste decorative materials such as internal and external wall tiles and floor tiles in buildings. It is widely used in decorative decoration places such as internal and external walls, floors, bathrooms, kitchens, etc.

Tile adhesive performance should not only pay attention to its operating performance and anti-slip ability. It will also pay attention to its mechanical strength and open time.

Cellulose ether in tile adhesive not only affects the rheological properties of ceramic adhesive, such as smooth operation performance, knife sticking, etc. It also has a strong influence on the mechanical properties of tile adhesive and the open time of tile adhesive.
When adhesive powder and cellulose ether coexist in wet mortar. Some data show that glue powder has stronger kinetic energy to adhere to cement hydration products. Cellulose ether is more present in the interstitial liquid. It affects the viscosity and setting time of mortar more. The surface tension of cellulose ether is greater than that of glue powder. More cellulose ether enriched on the mortar interface will be beneficial to the formation of hydrogen bonds between the base surface and cellulose ether.
Glue powder changes the consistency and smoothness of the system in the wet mixing state, and the addition of latex powder improves the cohesion. After drying, it provides the adhesion of a smooth and dense surface layer. Improve the interface effect of sandstone and pores. When the amount of addition is guaranteed, it is enriched into a film at the interface. Make tile adhesive flexible. Reduce the elastic modulus. Absorb thermal deformation stress to a large extent. It is also waterproof when it encounters water in the later stage, and the buffer temperature and material deformation are inconsistent.

The flexibility and rigidity of glue powder can generally be determined according to the glass transition temperature.

The glass transition temperature is below 0 degrees, which is more flexible. Which glue powder is needed in the mortar is generally determined according to the performance characteristics of the product.
Tile adhesives need to use glue powder with better adhesion. In wet mortar, the water in the mortar evaporates, and cellulose ether is enriched on the surface. A film will be formed on the mortar surface within 5 minutes, which will reduce the subsequent evaporation rate. As more water migrates from the thicker part of the mortar to the thinner part of the mortar layer, the film formed initially will be partially dissolved. The migration of water will bring more cellulose ether to the mortar surface.

Cellulose provides good water retention and workability for fresh mortar.

It plays a key role in the wetted area. In order to ensure the smooth progress of the hydration reaction, it can prevent the substrate from excessive water absorption and the evaporation of surface water. Due to its air entraining property, the bulk density of tile adhesive is reduced. It saves materials and reduces the elastic modulus of hardened mortar.

The film formation of cellulose ether on the mortar surface has a great influence on the performance of mortar.

If the film formed is too thin, it will be dissolved again, unable to limit the evaporation of water, and reduce the strength. If the film formed is too thick, the concentration of cellulose ether in the mortar interstitial liquid is high and the viscosity is high. It is not easy to break the surface film when the tiles are pasted.

It can be seen that the film-forming property of cellulose ether has a great influence on the open time.

The type of cellulose ether (HPMC, HEMC, MC, etc.) and the degree of etherification (substitution degree) directly affect the film-forming properties of cellulose ether. As well as the hardness and toughness of the film.
In addition to giving the mortar the above-mentioned beneficial properties, cellulose ether also delays the hydration kinetics of cement. This retarding effect is mainly due to the adsorption of cellulose ether molecules on various mineral phases in the hydrating cement system.
But in general, the consensus is that cellulose ether molecules are mainly adsorbed on hydration products such as C-S-H and calcium hydroxide. They are rarely adsorbed on the original mineral phase of clinker. In addition, due to the increase in the viscosity of the pore solution. Cellulose ether reduces the activity of ions (Ca2+, SO42-, …) in the pore solution, thereby further delaying the hydration process.
HPMC for tile adhesive