How to Handle Rust Stain Seepage on Exterior Wall GRC? Rust Treatment and Qinglong Group's Repair Technology System

Rust seepage on exterior GRC walls indicates that internal rebar or metal connectors have corroded, requiring a systematic four-step treatment approach of "detection and location, root-cause treatment, surface repair, and enhanced protection." Based on 28 years of maintenance experience, Qinglong Group has developed a standard workflow through projects such as Chimelong Ocean Kingdom in Zhuhai and the Shenzhen Yirui Biotechnology Building: first, locate corrosion points with infrared thermal imaging cameras and rebar scanners; chisel away the cover layer down to the rebar surface; sandblast to remove rust to Sa2.5 grade; apply epoxy zinc-rich primer (dry film thickness ≥60μm); restore the cross-section with polymer repair mortar (compressive strength ≥40MPa); and finally apply a fluorocarbon protective coating. During maintenance of the Nanning Wuxiang China Resources MixC project, we treated 137 rust spots with this solution, and 5-year follow-up after repair showed zero recurrence.

Corrosion Mechanism and Precise Detection

Rust seepage is usually caused by chloride ion attack or carbonation reaching the rebar surface. Qinglong Group uses the half-cell potential method (potential difference ≥-350mV indicates active corrosion) and chloride content testing (critical value 0.1% by mass) for precise location. In coastal projects, we have found that rust marks mostly occur at weak points such as panel joints and installation holes, which require focused inspection.

Eradication Repair and Material Selection

Thoroughly remove corrosion products down to bare metal; the repair mortar should be a low-shrinkage (≤0.02%) product with high bond strength (≥1.5MPa). Qinglong's patented migrating corrosion inhibitor (amine-based) can penetrate to the rebar surface to form a protective film. For large-area corrosion, a cathodic protection system is recommended, with a service life of up to 20 years.

Protection Enhancement and Preventive Measures

After repair, treat the surface with a silane impregnation agent (penetration depth ≥5mm) or fluorocarbon coating (salt spray resistance ≥3000h). Qinglong Group recommends establishing a regular inspection regime with a comprehensive inspection every 2 years to prevent problems before they arise. Scientific treatment can extend the service life of GRC exterior walls to over 50 years.