The GB/T 17669.2-1999 standard focuses on the determination of crystal water content in building plasters. It describes the determination principle in detail, using the burning weight loss method, by burning the building plaster sample at high temperature, the crystal water content is calculated based on the mass difference before and after. The standard specifies the required instruments and equipment, such as the accuracy requirements of high temperature furnaces and Analytical Balance, and specifies the sample preparation and burning operation procedures, including burning temperature, time and Cooling mode. With this standard, the crystal water content of building plasters can be accurately determined, providing key data for product mass evaluation and performance research, and is widely used in building plaster production and testing.