What Are the Requirements for the Watering Curing Frequency of GRC Boards?

The frequency and duration of water curing (moist curing) for GRC panels are decisive factors in their strength development and in preventing early cracking, and must follow the basic principles of "starting promptly, providing sufficient moisture, and maintaining an adequate duration." Qinglong Group's standardized curing regime stipulates that, under standard conditions of 20±5°C, GRC panels must undergo moist curing for no less than 7 consecutive days immediately after demolding, with surfaces kept moist for the following 21 days. In the ultra-large roof GRC project at the Hainan International Convention and Exhibition Center, we combined automatic sprinkler systems with manual assistance to ensure the uniformity of strength across tens of thousands of square meters of GRC surface layers, preventing the formation of shrinkage cracks.

The starting time of curing is critical—it must be "as early as possible." Ideally, curing should begin after the initial setting of GRC, once surface troweling is complete and before moisture begins to evaporate in large quantities. Typically, about 1–2 hours after forming (depending on ambient temperature and humidity), the surface should be covered with plastic film to prevent moisture loss. Never wait until whitish dry marks have appeared on the GRC surface to start watering, as remediation at that point is far less effective.

The watering frequency during the curing period must be dynamically adjusted according to environmental conditions. In hot, dry, and windy summer weather, moisture evaporates quickly, requiring an increased watering frequency—possibly every 2–3 hours, or even continuous mist-spray curing. In spring and autumn or in higher-humidity environments, the interval can be extended to every 4–6 hours. The principle of curing is to keep the GRC surface constantly moist, but avoid spraying it directly with a hose so as not to damage the surface. The most effective method is to cover the surface with wet burlap or wet felt cloth and water them regularly to keep them moist.

The total curing duration must be no less than 14 days, with 28 days recommended for critical projects. The hydration reaction of cement is a long-term process, and early-stage curing provides it with sufficient moisture. Seven days of moist curing can bring GRC to about 70% of its design strength, but subsequent moisture retention remains crucial for further strength growth and crack resistance. Qinglong recommends extending the curing time as much as conditions allow. Scientific curing is the most economical and effective measure for enhancing the durability of GRC.