How to Treat Mold on GRG Surfaces? How to Prevent Recurrence?

As one of the most widely used building materials in interior shaped decorative applications today, GRG has caused many project operators to struggle with mold growth on GRG surfaces—especially in environments such as the plum rain regions of southern China, underground commercial spaces, and high-humidity theaters and venues. Mold not only damages GRG's original clean, smooth curved appearance, but in severe cases can also erode the base structure and shorten the service life of components. As an engineering service provider with nearly 30 years of deep experience in GRG and other shaped building materials, we have combined hands-on experience from nearly 1,000 completed projects to compile a standardized treatment solution and long-term prevention logic for GRG mold, helping you avoid common treatment mistakes.

I. The Core Causes of GRG Mold: Don't Just Blame Product Quality

When many people discover mold on GRG, their first reaction is that they bought inferior materials. However, based on the hundreds of after-sales maintenance cases we have handled, more than 80% of GRG mold problems are directly related to later installation environments and operation and maintenance habits. First, GRG's base material is gypsum-based. Although basic hydrophobic treatment is applied at the factory, if the installation area has long-term air humidity above 70% and poor ventilation, water vapor will slowly penetrate into the interior of components, providing a breeding ground for mold. Second, many projects cut corners during the GRG topcoat construction stage, skipping the sealing primer process, or the topcoat's water resistance grade is insufficient, causing the surface waterproof barrier layer to fail. In addition, when GRG is installed in some underground spaces, the base keels are not treated for anti-corrosion and moisture resistance, and water vapor from keel condensation penetrates in reverse to the back of the GRG, slowly causing mold from the inside. In such cases, by the time mold spots become visible on the surface, large-scale substrate softening has already occurred on the back.

II. Standardized Treatment Steps for Mold on GRG Surfaces

Treatment methods differ clearly depending on the severity of GRG mold, and scrubbing randomly with bleach will only expand the damage: If the surface has only sporadic shallow surface mold spots, first cut off nearby water sources and temporarily use industrial fans to strengthen ventilation in the area. Once the component surface is completely dry, lightly sand away the mold spots with fine-grit sandpaper, clean off the dust, apply a coat of gypsum-based special sealing primer, then apply two touch-up coats matching the original topcoat's material and color number—after treatment, essentially no color difference marks will remain. If the mold has penetrated into the substrate, with surface bulging and powdering, treating the surface alone is not enough: first remove the entire GRG surface layer in the mold-affected area, check the humidity of the back substrate and the condition of the keels, and after confirming there is no continuous water vapor source, level the substrate with special GRG repair compound, then apply hydrophobic treatment, sealing primer, and topcoat restoration in sequence. In our past commercial building renovation projects, this treatment method has kept the recurrence rate within 5%. If mold appears on more than 30% of the area and the components have already become structurally loose, partial repair is not recommended—directly replacing the GRG components in the affected area is the most cost-effective option.

III. 3 Key Measures to Prevent GRG Mold Recurrence at the Root

To keep GRG from recurring mold after installation, don't rely solely on after-sales repairs—prevention must be implemented in advance across three project stages: design, production, and installation. First is customized adjustment on the production side: GRG for high-humidity areas should not use the conventional base formula; special anti-mold additives should be added during production, along with an additional double-layer hydrophobic coating process on the back. The custom GRG we produced for multiple underground commercial complexes in southern China has shown no mold problems for 8 consecutive years in an environment with 80% year-round humidity. Second is detail control during the installation stage: the base keels for GRG installation must be hot-dip galvanized for anti-corrosion; a 3-5mm air layer should be reserved between components and keels to avoid condensation caused by direct contact with thermal bridges; after installation, all concealed work must be completely dry before topcoat construction begins. Third is developing good daily operation and maintenance habits: during operation, do not regularly spray water directly onto GRG component surfaces for cleaning; regularly turn on ventilation and dehumidification equipment in high-humidity areas; reinspect the surface protective layer every 2-3 years and promptly reapply aged sealing topcoats.

FAQ:

1. Is wiping moldy GRG with bleach useful? Sporadic shallow surface mold spots can be temporarily wiped with diluted bleach, but this only removes surface mold and cannot solve the internal water vapor problem—recurrence within 1-2 months is highly likely, so it is not recommended as a long-term treatment solution.

2. Does all GRG need anti-mold treatment? Conventional dry indoor spaces do not need additional anti-mold processes, but for underground commercial spaces, theaters and venues, and indoor projects in southern China's plum rain regions, customized anti-mold adjustments are recommended in advance during the production stage to avoid excessive later operation and maintenance costs.

3. Does GRG mold affect structural safety? Short-term shallow surface mold does not affect structural strength, but if mold persists for more than half a year, the substrate becomes eroded by mold with powdering and softening, which reduces the component's impact resistance. In severe cases, there may be a risk of local detachment, requiring prompt treatment.