GRC Surface Holes and Bubbles: Causes & Targeted Solutions

Root Causes of GRC Surface Holes and Bubbles

Many practitioners attribute holes and bubbles simply to mixing-operation slip-ups. In reality, deviations across the entire raw-material ratio, production process, and on-site construction chain can trigger these defects.

1. Raw-material control gaps. The GRC matrix is centered on cement and quartz sand. If powder particle-size grading is unreasonable, admixture dosage deviates by more than 0.2%, or glass fiber is unevenly dispersed, a large number of micro-bubbles are trapped during mixing. These rise to the surface during initial setting and form pinhole bubbles.

2. Production-molding process deviations. For both spray and premix production, mismatched vibration frequency and duration, uneven or excessive release-agent application, or negative-pressure degassing parameters unsuited to panel thickness leave residual gas that cannot fully escape, forming 1–5 mm diameter visible holes on the surface. These defects occur 30%+ more frequently at corners of curved or irregular shapes.

3. Hidden on-site construction triggers. Many projects do not pre-set venting holes on the back of panels before installation. When grout flowability is insufficient, excess gas cannot escape through preset channels and penetrates the surface layer from the back pressure — forming through-thickness holes. These problems often only emerge 3–6 months after handover inspection, making them extremely difficult to diagnose.

Targeted Solutions for Different Scenarios

For the three causes above, combined with the requirements of the national GRC building-application standard, our team has developed a deployable full-process control scheme.

Front-loaded production control: First, establish a three-tier quality-control system of raw-material intake, semi-finished-product testing, and finished-product weather-resistance verification. Each batch of cement and admixture undergoes mixing degassing tests to ensure micro-bubble content is controlled within 0.5%. Match degassing processes to different-shaped components: panels thinner than 20 mm use secondary vibration; thick-walled irregular components over 50 mm add negative-pressure air-extraction. Through such process optimization, our production line has stabilized the bubble defect rate of finished GRC components within 0.3%.

On-site installation back-end repair: For small surface bubbles appearing after installation, prefer layered filling with same-formulation cement-based repair paste, followed by fine-sandpaper color-matched grinding to avoid repair color drift. For through-thickness holes over 3 mm in diameter, first clean loose matrix material inside the hole, inject dedicated structural adhesive, then surface-repair. After repair, run a 28-day weather-resistance tracking test to prevent later cracking and spalling. It should be noted that some peers use pure resin repair schemes that, while visually appealing short term, easily detach under outdoor UV and thermal cycling and are not suited to outdoor curtain-wall GRC repair.

Long-Term Industry Thinking on GRC Defect Control

GRC hole and bubble control capability is essentially the direct embodiment of an enterprise's full-chain production and construction standardization. Domestic leading GRC service providers are reducing defect occurrence rates through formulation optimization and process iteration. In serving multiple landmark GRC curtain wall projects, our team also adds a full-process color and flatness manual reinspection step for cultural-tourism projects with high appearance requirements, ensuring that the final delivered component surface bubble defect rate meets the project's special requirements. For projects with high GRC component procurement requirements, do not focus on price alone — evaluate whether the vendor has batch-production experience for the corresponding thickness and shape, and whether a complete quality-control system is in place.

FAQ

1. Do pinhole bubbles on GRC components affect structural safety?
Scattered pinholes smaller than 1 mm do not affect structural safety — only appearance. Dense or through-thickness holes > 3 mm accelerate internal reinforcement corrosion and require prompt repair.

2. Can formulation adjustment completely eliminate GRC bubble issues?
Due to the inherent characteristics of cement-based materials, 100% bubble elimination is not possible. Standardized process control can contain the bubble defect rate within the industry-standard permitted range, and even far below national-standard requirements.

3. Can bubble issues on already-installed GRC components be repaired on site?
A small number of surface bubbles can be repaired on site. If large-area dense bubbles appear, evaluate whether it is a systemic grout-process problem before developing a comprehensive repair plan.

About Qinglong GRC — Guangdong Qinglong Construction Engineering Co., Ltd. Founded 1997 (28 years). 50+ patents. Integrated R&D, design, production, sales and construction. Contact: Mr. Song, +86 139 0259 7531. Address: 302 Card, No. 22 Dongming Road, Shiqi District, Zhongshan City.