Preparing a surface for painting is an essential part of general ship maintenance. Here are the steps involved in preparing a surface for painting:
- Cleaning: Clean the surface using a water-soluble detergent and high-pressure fresh water. Remove salt, oil, grease, loose coating, dirt, and detergent before de-rusting.
- De-rusting: Turn smaller patches of rust into one larger area by removing the paint between the rust patches. Remove rust manually or mechanically using power tools. Mechanical removal is recommended for better results. Limit edges and feather them by grinding or sanding to ensure proper adhesion.
- Preparation and Priming: Sound preparation is crucial for successful painting. Remove dirt, moisture, rust, salt deposits, grease, and oil that hinder paint adhesion. Smooth, shiny surfaces should be roughened, and certain metals may require pretreatment. Common methods for cleaning steelwork include mechanical wire brushing, flame cleaning, and grit or wet sandblasting.
- Primers for Iron and Steel: Primers for iron and steel must help inhibit rust and usually contain rust-inhibitive pigments in a suitable vehicle. Examples of rust-inhibitive pigments include red and white lead, basic lead sulphate, chromates of lead and zinc, and metallic (dust) lead and zinc. Lead-based paints should not be used in refrigerated spaces, areas used for foodstuffs, or on galvanized metal.
- Aluminum, Copper, etc.: Adhesion of paint to surfaces such as aluminum, copper, brass, and lead is usually poor. These surfaces should be pretreated or abraded before priming with suitable primers like zinc chromate primer. Some flaking may still be expected.
- Steelwork: Before cleaning and priming, perform steelwork, which involves rounding sharp edges, grinding off welding beads and slag, repairing surface defects, and grinding rough manual welds or gas-cut edges.
- Pre-Treatment: Once steelwork is completed, pre-treatment can begin. Proper cleaning is crucial to remove contaminants and impurities like oil, grease, salt, dust, and dirt. Blast-cleaning, ultra-high-pressure water cleaning, or mechanical cleaning methods can be used depending on the substrate and project requirements.
- Blast-Cleaning: This method removes old paint, rust, and scales, providing a clean and rough surface. Dry blast-cleaning generates dust, while slurry and wet blast-cleaning use water to reduce dust but create flash rust. Use non-metallic abrasives for stainless steel, aluminum, and galvanized steel.
- Ultra High-Pressure Water Cleaning: This method removes contamination and old paint by applying water under extremely high pressure. It avoids dust but can cause flash rust. Clean water should be used to prevent contamination.
- Mechanical Cleaning: Use mechanical tools like steel brush grinding equipment or machining for surface cleaning. This method may not achieve the same degree of cleanliness and roughness as blast-cleaning, reducing adhesion between the substrate and paint system.
By following these steps, the surface will be properly prepared for painting, ensuring better paint adhesion and long-lasting protection.