A novel approach for improving the water resistance of gypsum plaster by internal mixing hypromellose and external coating waterproofing agent

The utilization of gypsum plaster in humid environments is strictly limited by the poor waterproof performance and strong water absorption. To solve this problem, the self-prepared organic waterproofing agent in combination with hypromellose were used to improve the water resistance of gypsum plaster. The results showed the addition of organic waterproofing agent or hypromellose could improve the softening coefficient, decrease the water-absorption rate, and prolong the setting time of gypsum plaster. Compared with single waterproofing agent or hypromellose, the internal mixing hypromellose and external coating waterproofing agent is a more effective method to improve the water resistance, the softening coefficient of gypsum plaster increased from 0.57 to 0.81, and the water-absorption rate decreased from 20.4% to 10.54%. The waterproofing agent could form a hydrophobic film on the surface of hardened paste, which could effectively hinder the water molecules penetrating into the hardened paste. Besides, the internal mixing hypromellose and external coating could reduce the porosity, capillary water absorption and hygroscopic capacity. Hence the waterproof performance of gypsum plaster was enhanced. This research provided an effective approach for improving the water resistance of gypsum plaster by internal mixing hypromellose and external coating the waterproofing agent.