Cellulose ether, taking hydroxypropyl methyl cellulose (HPMC) as an example, is the etherification of natural cellulose. Because it has good water retention and thickening effects on mortars and can significantly improve the workability of mortars, cellulose ethers are the most commonly used water-soluble polymers in mortars. While HPMC enhances the workability of the mortar, it also has an impact on the structure and performance of the mortar. For ordinary commercial mortar or dry powder mortar, HPMC can reduce the consistency (thickening) of the slurry, change the morphology of cement hydration products, and affect the pore structure of the slurry, making the hardened cement slurry loose and porous, resulting in reduced strength; For EPS insulation mortar, the effect mechanism of HPMC on the performance of the mortar is more complicated.
The MIKEM test shows that when the HPMC content is 0.2%, the consistency of the thermal insulation mortar slurry reaches the maximum, and the water retention rate is higher; continue to increase the HPMC content, the consistency begins to decrease, but the water retention rate is not improved significantly. It can be seen that to ensure the excellent workability of EPS insulation mortar, the optimal mixing amount of HPMC is 0.2% of the cement quality.
The MIKEM test showed that the bond strength of the mortar without HPMC was higher than that of the HPMC mortar. With the increase of HPMC content, the bond strength gradually increased. This rule is that the bubbles introduced by HPMC have a more significant impact on the tensile strength of the mortar. With the increase of the HPMC content, the free water in the mortar decreases, the encapsulation of the EPS particles by the slurry increases, and the bonding strength increases. Therefore, redispersible latex powder (RDP) is generally used in EPS insulation mortar to increase the bonding strength.
The MIKEM test shows that with the increase of HPMC, the water retention effect is enhanced, and the number of introduced pores increases. After the content exceeds 0.2%, the consistency and fluidity are significantly reduced. There are fewer pores in the mortar without HPMC, and the pore diameters are all above 500um. It can be analyzed that the pore diameter of HPMC introduced is 200-500um, and the pores of 500-~800um may be the pores left by the stirring of air and water evaporation.
Conclusion:
1) HPMC has good water retention and a thickening effect. With the increase of its content, the water retention rate of EPS insulation mortar gradually increases, and the consistency first increases and then decreases sharply. The optimal content is 0.2%.
2) EPS insulation mortar mixed with a small amount (0.05%) of HPMC because HPMC improves the encapsulation of the EPS particles by the slurry. It has less air entrainment and higher strength. With the increase of its content, the strength of the mortar first decreases and then increases, and the strength is the lowest when the consistency is the highest; The addition of HPMC will reduce the tensile bonding strength of EPS insulation mortar so to ensure the performance of the mortar, it should be used in conjunction with RDP.
3) HPMC has a strong air-entraining effect and affects the strength of the mortar. As its content increases, the average pore diameter of the mortar decreases, and the pore diameter of the introduced bubbles is 200-500um.
It is recommended to use our MelaCollTM cellulose products in EIFS applications to improve processability and enhance bond strength. Our MikrantTM RDP products are also widely used in EIFS to enhance adhesion and cohesion, increase flexibility and impact resistance, improve surface abrasion resistance, and avoid crack and lump formation.
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