1.How to prepare the surface before repair?
Clean the damaged area: Use a wire brush or sandpaper to thoroughly remove loose zinc, rust products (red rust) and dirt until the metal base is exposed.
If there is oil, clean with a solvent (such as acetone) and dry.
Edge preparation: Use sandpaper or a small grinding wheel to grind the damaged edge into a slope (30°-45°) to form a smooth transition area (avoid steep drops in coating).
Rust removal level: The steel surface of the substrate must reach ISO 8501-1 St3 level (no visible grease, scale, rust, and the metal substrate shows metallic luster).
Clean and dry: Blow away dust with compressed air to ensure that the surface is dry and free of moisture.
2.How to repair small scratches and cuts?
Preferred solution: cold galvanizing paint
Advantages: good electrochemical compatibility, providing sacrificial anode protection, matching the potential of the galvanized layer.
Key points for construction:
Product selection: Epoxy zinc-rich paint or inorganic ethyl silicate zinc-rich paint with zinc powder content ≥92%.
Coating method: Small area: Use a brush or fine brush to apply, avoiding contamination of the surrounding galvanized layer.
Strip damage: spray or brush, the width covers the extension of the damaged area ≥20mm.
Film thickness control: single wet film thickness ≈120μm, dry film ≈80μm (2-3 coats are required to achieve a total dry film thickness ≥ the original galvanized layer thickness).
The interval between each coat is based on the product instructions (usually it can be recoated after the surface is dry).
Curing: 7 days of room temperature curing to achieve the best performance (if urgently needed, low temperature baking can be accelerated to cure).
3.How to repair extensive damage?
Thermal spraying zinc/aluminum
Advantages: The repair layer has similar performance to hot-dip galvanizing and has a long service life (more than 20 years)
Key points for construction: The surface needs to be sandblasted to Sa2.5 level (ISO 8501-1), with a roughness of Ra=60-100μm. Spray zinc wire or aluminum-zinc alloy wire (such as ZnAl15), with a thickness ≥1.2 times the original galvanized layer (usually 150-200μm).
Sealing treatment is recommended after spraying: Apply epoxy micaceous iron or polyurethane coating to enhance sealing.
4.How to repair irregular surfaces, bolt heads, corners and other difficult-to-spray areas?
Zinc-based repair paste/stick
Squeeze the paste to the damaged area and use a scraper to compact and fill it.
The zinc rod needs to be melted with a special soldering iron (low temperature) before applying.
After curing, polish it flat, and the dry film thickness is ≥150μm.
5.How to repair extremely small pinholes?
Galvanizing repair agent
Method: Apply a repair solution containing zinc ions (such as zinc depositing agent) to deposit the zinc layer through a chemical replacement reaction.
Limitations: The film is thin (≈10μm) and needs to be strengthened with cold galvanizing paint.