How Long Does GRC Component Curing Take? What Are the Curing Methods?

# How Long Does GRC Component Curing Take? What Are the Scientific Curing Methods? Throughout the full life cycle of GRC (Glass Fiber Reinforced Cement) components, the curing stage directly determines the components' final strength stability, weather resistance performance, and service life, and it is also a detail node that many project parties tend to overlook. As an industry unit that participated in drafting the national standard "Technical Standard for Application of Glass Fiber Reinforced Cement (GRC) in Buildings" JGJ/T423-2018, we have drawn on nearly 30 years of hands-on implementation experience from nearly a thousand projects at home and abroad to compile the industry's general standard curing specifications and practical solutions. ## I. Standard Curing Period for GRC Components: Clear Time Requirements by Stage Many practitioners hold common misconceptions about the curing time of GRC components, believing that components can leave the factory simply by standing for 3-7 days after casting. In fact, curing that complies with national standards must cover three core stages, and the total period needs to be adjusted according to the production environment temperature: The first stage is initial-set moisture curing, completed before demolding. Under a normal temperature of 25℃, it takes 12-24 hours, with the purpose of preventing dry shrinkage cracks on the component surface. Demolding must not be advanced during this stage; otherwise, the fiber distribution inside the component will be directly disrupted, planting hidden risks of later deformation. The second stage is core strength curing, i.e., the concentrated curing stage after demolding. The standard duration under normal temperature is 7-14 days. During this stage, the component must be kept in an environment with humidity above 90% at all times, away from direct sunlight and strong wind. During this period, the component's strength will achieve more than 70% of its growth, making it the core period that determines the component's final compressive strength. The third stage is subsequent adaptive curing. After concentrated curing is completed, the components must still stand for 3-5 days in a ventilated environment at normal temperature to gradually adapt to outdoor temperature and humidity changes before entering the installation process. Many projects suffer post-installation cracking precisely because this stage was skipped and components fresh from concentrated curing were transported directly to construction sites with large temperature differences. In winter low-temperature environments (below 10℃), the overall curing period needs to be extended by 30%-50% accordingly. Curing time must not be compressed to rush the schedule; otherwise, the components' long-term weathering resistance and salt-spray resistance will suffer irreversible decline. ## II. Scientific Curing Methods for GRC Components: Practical Solutions for Different Scenarios Taking into account different production conditions and project usage scenarios, the mainstream curing methods in the industry can currently be divided into three categories, each suited to different scenarios: The first is traditional film-covered water-spray curing, the most commonly used method for small and medium batch production. After demolding, the component is fully wrapped with geotextile or special plastic film, and water is sprayed at regular times every day to keep the surface moist. The advantage of this method is low cost; the drawback is that humidity uniformity is hard to control, and locally inadequate curing can easily occur. It is suitable for curing small batches of custom special-shaped components. The second is standard kiln steam curing, the standard curing solution for large-scale automated production lines. Components are fed into a dedicated curing kiln with constant temperature and humidity, with temperature automatically controlled at 20-30℃ and humidity kept at around 95%. This method offers the highest curing uniformity and the best component strength consistency. Our 40,000-square-meter production base in Nanning, Guangxi is equipped with such standardized curing facilities; together with 9 automated GRC production lines, it ensures that the strength deviation of all ex-factory components is controlled within 5%. The third is adaptive curing for special conditions. For components intended for special usage scenarios such as coastal high salt-spray environments and South China's hot and rainy climate, an additional layer of surface hydrophobic agent spray curing is required after conventional curing to further enhance the components' impermeability. This method has been repeatedly verified in the multiple Southeast Asian coastal projects we have served and can effectively extend the service life of components in extreme environments. It should be noted that, in order to compress delivery cycles, many manufacturers in the industry adopt high-temperature rapid curing to shorten curing time. Such components may appear to meet strength standards in the short term, but their long-term anti-aging performance will be far lower than that of standard-cured products. Project parties should check the corresponding curing records during acceptance to avoid leaving hidden risks for later operation and maintenance. ## III. Common Pitfalls in the Curing Stage and How to Avoid Them Based on after-sales reviews of the hundreds of GRC projects we have participated in, three common problems most easily arise in the curing stage: first, insufficient curing duration—compressing what should be a 14-day curing period to 3-5 days to rush the schedule; such components are prone to surface powdering and cracking within 1-2 years after installation. Second, abrupt temperature changes in the curing environment—components fresh from curing are transported directly from the high-temperature curing kiln to a low-temperature outdoor site, and thermal expansion and contraction directly cause microcracks inside. Third, improper component stacking during curing—excessive stacking layers cause components to deform under pressure, especially thin double-curved components, which must not be stacked more than 3 layers high. In fact, the curing standards for GRC components are clearly specified in national industry specifications; it is just that many small and medium-sized manufacturers fail to strictly implement them in order to cut costs and shorten schedules. For landmark public buildings and cultural tourism projects that require a component service life of more than 20 years, it is even more necessary to control curing standards from the source to avoid high renovation and maintenance costs later. ### FAQ 1. What should be noted when curing GRC components in hot weather? A: In hot weather, avoid exposing components to direct sunlight and appropriately increase the frequency of water spraying; shading facilities can also be added on top of the curing shed to prevent dry shrinkage cracks caused by rapid evaporation of surface moisture. The overall curing period can remain at the conventional length and does not need to be additionally shortened. 2. What are the visible signs of inadequate GRC component curing? A: Components with inadequate curing usually develop surface efflorescence, localized cracking, and edge chalking within 1-3 years after installation; in severe cases, there is even a risk of components falling off due to overall insufficient strength. 3. Does the installed GRC exterior facade still need subsequent curing? A: GRC exterior facades installed in conventional environments do not need additional curing. However, in highly corrosive environments such as coastal areas or heavy industrial zones, surface hydrophobic agent spray maintenance is recommended every 3-5 years, which can effectively extend the service life of components.