How to Moisture-Proof GRG Components? Can They Be Used in Humid Environments?

As the mainstream material for interior free-form decorative scenarios in theaters, exhibition centers, and commercial complexes, the moisture-proof performance of GRG components has always been a core consideration for designers and contractors. Many projects have experienced problems such as dampness and mold on interior components during the plum rain season, finish peeling, and reduced structural strength due to overlooked moisture-proofing details. As a result, many clients directly ask: How should GRG components be treated for moisture resistance? Can they be used in humid environments? As a service provider with nearly 30 years of deep experience in the free-form building materials field, we have drawn on hands-on experience from nearly 1,000 completed projects to provide a professional reference plan that can be put into practice directly.

I. Core Principles and Common Misconceptions of GRG Component Moisture-Proofing

First, it is important to clarify the base material properties of GRG itself: GRG stands for Glassfiber Reinforced Gypsum. The gypsum base material has a relatively high porosity, so in environments where the relative humidity of the air remains above 85% for long periods, problems can indeed occur, such as free water penetrating the pores, causing slight expansion of the gypsum components and blistering or peeling of the attached finishes. However, this does not mean that GRG cannot be used in humid environments. In the vast majority of cases where moisture-proofing fails, the root cause is omissions in the early-stage treatment rather than defects in the material itself. There are currently three main common misconceptions in the industry: The first is the belief that simply applying waterproof paint to the component surface achieves full-cycle moisture protection, while ignoring the sealing of component joints and the connections with the base layer—which are precisely the core channels for moisture intrusion. The second is excessively pursuing moisture-proof performance by adding large amounts of waterproof additives to the base material, which instead destroys GRG's inherent slightly breathable texture, causing internal moisture to be unable to escape and leading to harder-to-treat internal mold. The third is focusing only on the moisture-proofing of the components themselves while ignoring the supporting moisture-proofing measures for the indoor ventilation system and the base keels, ultimately resulting in keel corrosion that causes component deformation.

II. Full-Process Solution for Standardized GRG Component Moisture-Proofing

Based on the logic of the Technical Standard for Building Application of Glass Fiber Reinforced Cement, which we participated in compiling, and implementation experience from multiple projects in high-humidity southern regions, a qualified GRG moisture-proofing treatment needs to cover three core stages: The first is pre-treatment during base material production: During the GRG slurry preparation stage, add a dedicated gypsum waterproofing modifier at a ratio of 0.8%-1.2%, while ensuring uniform dispersion of the glass fibers to avoid uneven local base material density. Components treated at this stage can achieve a strength retention rate of over 85% after 72 hours of immersion, far higher than the baseline of around 40% for ordinary GRG. Note that the additive ratio in this step must be strictly controlled to avoid excess affecting the component's molding precision—especially for curved components, where an excessive additive ratio can easily cause deformation after demolding. The second is sealing treatment during component installation: After the components are joined, first fill all joint gaps with a dedicated gypsum sealant. Once the sealant has fully cured, grind the joint areas smooth. Then uniformly apply two coats of flexible waterproof coating to the entire back of the components (the side in contact with the keels and the base layer). Make sure the coating fully covers all areas of the component backs, including the contact points with the keels, to avoid any omissions. The third is sealing treatment during the finishing stage: Before finishing the front face of the components, first apply a coat of sealing primer uniformly. The sealing primer must fully penetrate the pores on the GRG surface. After the primer is completely dry, proceed with subsequent finishing work such as latex paint or art paint. For special long-term high-humidity scenarios such as underground commercial spaces and areas near bathrooms, an additional transparent hydrophobic coating can be applied after the finishing work, which does not affect GRG's appearance and texture while further reducing the surface's ability to absorb moisture.

III. Additional Considerations for GRG Applications in Humid Environments

For long-term humid scenarios such as southern plum rain regions, underground spaces, and waterfront environments, two additional optimizations are needed beyond the standard treatment process above: First, prioritize galvanized light steel keels for the base keel system and avoid ordinary steel keels. At the same time, install rubber shock-absorbing gaskets at the contact points between the keels and GRG components, which both isolates the condensation risk caused by cold bridges and prevents scratching damage to the waterproof coating during component installation. Second, reserve concealed ventilation channels at the design stage to ensure air circulation in the cavity area between the GRG components and the base layer, preventing moisture from accumulating long-term in enclosed spaces. Based on actual implementation data, GRG components treated according to the above process have shown no problems of dampness, mold, or reduced structural strength after more than 10 years of continuous use in environments where the relative humidity remains at 70%-90%. This has been verified in multiple underground commercial projects in South China and exhibition venue projects in coastal cities.

IV. FAQ on GRG Moisture-Proofing

1. How should localized dampness be handled in GRG components that have already been installed? Answer: First, check whether the base layer corresponding to the damp area has water pipe leakage or condensation problems. After addressing the source of the leak, grind the finish and surface layer of the damp area down to the dry base material, reapply a waterproof sealing layer, and then restore the finish.

2. Can GRG be used directly in bathrooms, swimming pools, and other scenarios with long-term exposure to open water? Answer: Direct use is not recommended. For scenarios with long-term direct contact with open water, materials such as GRP and waterproof GRC should be preferred. If GRG shaping must be used, multiple layers of rigid waterproof encapsulation need to be added on top of the standard moisture-proofing process, at a cost far higher than other alternative materials.

3. Are the moisture-proofing treatment standards for GRG components from different manufacturers universal? Answer: The core treatment logic is universal, but base material formulations differ between manufacturers, so the corresponding waterproof additive ratio needs to be adapted based on the manufacturer's base material parameters. Directly applying third-party treatment parameters is not recommended.