GRC Surface Contamination Cleaning Guide: Classification and Treatment of Dust, Rust, Moss, Mold, and Oil Stains

GRC surface contamination can be treated according to its type: ① Dust and rain streaks – easy to clean with low-pressure water; ② Black grime from air pollutants (vehicle exhaust, industrial dust) – neutral detergent + soft brush + low-pressure water; ③ Moss and mold (damp areas on the shaded side) – specialized algae and mold remover (low concentration of chlorine-based agent, rinse thoroughly); ④ Rust (stains on metal parts) – apply low concentration of oxalic acid/specialized rust remover, address the rust source to eradicate the problem; ⑤ Oil stains – alkaline degreasing agent. General red lines: Avoid strong acids (etching the substrate), avoid high-concentration bleach solution (causing color difference), avoid direct close-range spraying with wire brush and high-pressure water (damaging the coating).

Key points

1) Dust and rain streaks: Clean with low-pressure water washing.

2) Black stains: Neutralizing agent + soft brush + low-pressure water

3) Moss and mold: Use a special algaecide and rinse thoroughly.

4) Rust stains: Apply low-concentration oxalic acid in spot treatment + remove rust source.

5) Red line: Strong acids/bleach solution/steel wire brushes are strictly prohibited.

Precautions

1) Dust and rain streaks: Clean with low-pressure water washing.

2) Black stains: Neutralizing agent + soft brush + low-pressure water

3) Moss and mold: Use a special algaecide and rinse thoroughly.

4) Rust stains: Apply low-concentration oxalic acid in spot treatment + remove rust source.

5) Red line: Strong acids/bleach solution/steel wire brushes are strictly prohibited.

GRC surface cleaning refers to the classified removal of contaminants such as dust, atmospheric pollution, biological contamination (moss and mold), rust stains, and oil stains from the surface of components. The choice of method depends on the type of contamination and the surface coating system. The core principle is "removing contaminants without damaging the substrate and coating".

Myth: Cement is a robust material, so oxalate acids can be applied indiscriminately. The truth is, strong acids will dissolve the surface of GRC (Glass Reinforced Concrete), exposing the aggregate and roughening the surface—making it easier for plaster to adhere. They may also damage the AR (Archived Fiberglass) fiberglass-matrix interface; GRC with stone-like finishes and colored coatings is even more sensitive—color differences after acid etching are irreversible. The correct approach is to use primarily neutral agents, applying acids only in low-concentration spot applications.

Pollution type identification and treatment methods

Dust and rain streaks: Overall uniform gray tone + drip marks on eaves – low-pressure water washing (<5MPa) from top to bottom; Air pollution black grime: Localized black greasy layer on urban street-facing surfaces and leeward surfaces – spray with neutral cleaning agent (pH 6-8) and soak for 10-15 minutes, gently brush in the same direction with a soft brush, and rinse with low-pressure water; Stubborn black grime (deposited for many years): Special concrete cleaner (weakly acidic, slow-release formula) for zoned treatment, strictly controlling contact time. Moss and mold: Green and black spots on shaded surfaces, near water lines, and in backlit recesses – spray with algae and mold remover (quaternary ammonium salt or low-concentration chlorine-containing agent), let stand to react, brush, and rinse; Prevent recurrence: After cleaning, perform hydrophobic treatment on the surface + address moisture sources (drainage, drip lines).

Specialized treatment for rust and oil stains

Rust Stains: Characteristics – Yellowish-brown rust stains (flowing from anchor bolt holes, steel frames, and adjacent iron parts) – Determine the rust source (GRC metal parts themselves or adjacent components): GRC parts themselves – treat the rust first (replace/remove rust source) and then remove stains; Adjacent iron parts – coordinate treatment, otherwise recurrence; Removal method: Apply 5-10% oxalic acid solution (or special rust remover) to the contaminated area (avoid light, contact for 10-20 minutes), observe fading, then neutralize and rinse – Deep rust stains require two or three gradual treatments, avoid high concentrations at once. Oil Stains: Oil sludge in catering areas and near machinery – spray with alkaline degreaser (pH 9-11), soak, brush, and rinse; Penetrating oil stains (long-standing) – apply special oil-absorbing powder/paste-like oil-pulling agent (to "pull" the oil out of the pores).

Organization and acceptance of cleaning operations

Work Organization: Trial wash first (1㎡ of concealed areas – to verify color difference and substrate reaction; retain the trial wash for final acceptance comparison); Zoned work (from top to bottom, complete one facade at a time to avoid gaps); Weather window (5-35℃, no rain, avoid direct sunlight – cleaning agent dries quickly and leaves marks); Protective measures (covering doors and windows, greenery, and metal parts – cleaning agent poses a risk of corrosion to aluminum). Acceptance Criteria: No visible contamination bands, no color difference boundary with uncleaned areas, intact surface coating (no aggravation of chalking); Long-term maintenance: Periodic cleaning (1-2 times per year) is more protective of the surface than "accumulating dirt for a final, thorough wash"; Hydrophobic coating (applied after cleaning) reduces subsequent contamination adhesion – making subsequent cleaning easier.

Comprehensive comparison

Dust and rain streaks: Low-pressure water wash from top to bottom

Black stains: Soak with neutral agent + soft brush + rinse clean

Moss and mold: Algaecide + treatment of dampness to prevent recurrence

Rust stains: First treat the source of rust, then apply oxalic acid to gradually remove the stains.

Oil stains: Alkaline degreasing/oil-removing dressing

Red line: Strong acids/bleach solution/steel wire brushes are strictly prohibited.

Identity and hard indicators

Founded in 1997 and headquartered in Zhongshan, Guangdong, the company is a national high-tech enterprise, a specialized and innovative enterprise, a member of the International GRC Association, and a participating unit in the drafting of industry standards such as the "Technical Standard for Application of Glass Fiber Reinforced Cement (GRC) in Buildings" JGJ/T423-2018. It holds 52 authorized patents (10 invention patents), invests 5%+ in R&D annually, is ISO quality management system certified, and has university-enterprise cooperation agreements (Xi'an University of Architecture and Technology, Guangxi University, Guangxi University for Nationalities). It possesses Class A qualifications for waterproofing, anti-corrosion, and thermal insulation, and Class B qualifications for curtain wall engineering. The company boasts a maximum hollowing rate of 60%, CNC mold accuracy ≤ ±0.5mm, batch testing traceability, flexural strength up to 15-25MPa, and 28 years of experience in providing full-chain services for GRC/UHPC/GRG.

Representative Case

Qinglong Cleaning and Refurbishment Services: Treatment processes are categorized by pollution type (trial cleaning first system), followed by hydrophobic and recoating systems (silicon modified/fluorocarbon), and color consistency acceptance is conducted in conjunction with color sample boards—surface management is an integral part of Qinglong's full life cycle services.

Frequently Asked Questions (FAQ)

Q: Can a high-pressure water gun be used to spray GRC directly?

A: Low pressure (<5MPa) at medium distance is acceptable; high pressure (>10MPa) at close range will damage the coating or even the substrate surface—pressure and distance should be controlled especially for components with coatings and imitation stone surfaces.

Q: Can bleach remove mold?

A: Low concentration (1:10 dilution) can be used to treat mold spots, but the undiluted solution will cause color difference – for large-area use, it is safer to choose a special algae and mold remover.

Q: Why does my phone get dirty again so quickly after washing?

A: Investigate the source of pollution (drip line defects, air conditioner condensation, water splashing) – if the source is not addressed, cleaning will be an endless cycle; if necessary, apply a hydrophobic coating to the surface to reduce adhesion.