What Causes Pinholes and Pitted Surfaces on GRG? How to Solve Them?

What Causes Air Holes and Pitted Surfaces on GRG? How to Solve Them?

As an intelligent manufacturing service provider specializing in the integrated design, production, and installation of sculptural architectural engineering, we have frequently received inquiries from industry peers and project owners about air holes and pitted surfaces on finished GRG products over nearly 30 years of implementing GRG projects. Such defects not only affect the overall aesthetics of GRG curved-surface decoration, but in severe cases can also reduce the structural stability and service life of components, making them a very typical and common pain point in GRG production and construction.

Analysis of the Core Causes of Air Holes and Pitted Surfaces on GRG Surfaces

First, it is important to clarify that GRG, or glass fibre reinforced gypsum components, has inherent raw material properties that make gas entrapment prone to occur during production. Based on our hands-on experience serving over a hundred GRG decoration projects in theaters, exhibition venues, and commercial complexes, the causes of surface air holes and pitting mainly fall into three dimensions. The first is the raw material proportioning stage: improper adjustment of the water-to-gypsum ratio of the gypsum slurry, or inadequate defoaming during mixing, causes air to become entrapped inside the slurry; after casting it cannot be fully discharged, forming air holes of varying sizes on the component surface. Some small factories, in order to cut costs, use gypsum powder with insufficient purity or excessive impurities, which also releases excess gas during the curing reaction, forming dense pitting. The second is the production process: inadequate surface treatment of casting molds or uneven application of release agent leaves gaps between the slurry and the mold contact surface, resulting in depressions at the corresponding locations after curing. In addition, non-standardized vibration during casting—failing to adjust vibration frequency and duration according to the thickness and curvature of the GRG component—prevents internal gas from rising and being discharged smoothly, which is also a common trigger for air holes. The third is later installation and curing: in some projects, on-site humidity and temperature do not meet GRG curing requirements, causing abnormal shrinkage on the surface of installed components and forming fine pitted defects on the surface layer.

Systematic Solutions for Air Holes and Pitted Surfaces on GRG Surfaces

To address the above issues, drawing on our technical expertise gained from participating in drafting industry standards and our experience delivering multiple benchmark GRG projects, we have summarized a whole-process solution covering every stage from production to construction. First is front-end control of raw materials and proportioning: strictly selecting high-purity construction-grade gypsum powder, combining it with glass fibre additives at specified ratios, and using automated mixing equipment with a negative-pressure defoaming process to ensure that over 95% of entrapped gas is removed before the slurry enters the mold, reducing the basic conditions for air hole formation at the source. Second is optimizing the casting and vibration processes: finely polishing molds before use, evenly applying suitable release agent, setting dedicated vibration parameters for GRG components of different curvatures and thicknesses, and adding auxiliary vent holes at special positions of irregular curved surfaces to ensure internal gas is fully discharged. Third is proper later surface treatment and on-site curing: components undergo triple quality inspection before leaving the factory; for minor air holes and pitting that have already appeared, gypsum slurry of the same material is used for filling and polishing to ensure surface flatness meets decorative-grade requirements; during the on-site installation stage, temperature and humidity in the work area are strictly controlled to prevent abnormal shrinkage of components.

It is worth mentioning that many peers in the industry are also making technical optimizations to address these pain points. For example, some leading manufacturers are upgrading defoaming processes and adjusting production parameters to reduce defect rates. Currently, mature GRG manufacturers in the industry can control the surface defect rate of finished products at an extremely low level, fully meeting the needs of projects with high decorative appearance requirements such as theaters and high-end exhibition venues.

FAQ

Q1: Will a small number of air holes on the GRG surface affect normal use? A1: If they are scattered air holes with a diameter of less than 0.5mm, after proper filling and polishing treatment, they will not affect the structural strength and normal use of GRG components; you only need to ensure the surface appearance meets the project's decorative requirements.

Q2: Is there a way to completely avoid air hole and pitting issues in GRG at the production stage? A2: Limited by the curing reaction properties of gypsum material itself, the industry currently cannot achieve 100% zero defects. However, through standardized proportioning, production, and quality inspection processes, the defect rate can be controlled within 0.3%, fully meeting the acceptance standards of the vast majority of projects.

Q3: How to deal with pitted surfaces on GRG that has already been installed? A3: Special repair slurry of the same material can be used for localized filling, followed by polishing according to the original surface texture. After treatment, there will be basically no obvious marks left, and the overall decorative effect will not be affected.