Manhole covers are exposed throughout the year. Crushed by vehicles, battered by wind and rain, and corroded by acids and alkalis, their anti-corrosion coatings are prone to peeling, flaking, and rusting. This not only affects the appearance, but also accelerates the corrosion of the manhole covers themselves and shortens their service life. The key to coating repair lies in three points: thorough rust removal, matching paint, and standardized construction.

I. Prepare the Surface Before Repair

First, scrape off the lifted and loose coating on the manhole cover surface, and rinse off sand, mud, and oil stains with a high-pressure water gun. For a firmly adhered old coating, grind it off with an angle grinder fitted with a steel wire brush. Focus on rusted areas and keep grinding until the natural luster of the metal is exposed—don’t leave any rust at all, otherwise the new coating won’t stick firmly.

After rust removal, the surface should meet the near-white grade or thorough manual rust removal grade standard, and the surface should maintain a slight roughness for optimal coating adhesion. Wipe off dust with a clean cloth after treatment, and apply paint within 4 hours to prevent re-rusting. For local damage, mark 2-3 centimeters outward from the damaged area to ensure full repair coverage. If the coating fails over a large area, it’s recommended to re-spray the entire surface to avoid color differences and poor adhesion.

II. Choose the Right Paint and Mix It Properly

Manhole covers typically utilize a three-layer paint system consisting of a primer, an intermediate coat, and a topcoat. When repairing manhole covers, the new paint must be compatible with the existing coating. For ductile iron manhole covers, it is recommended to use an epoxy zinc-rich primer, followed by an epoxy micaceous iron oxide intermediate coat, and finishing with a polyurethane or fluorocarbon topcoat. These choices provide enhanced weather and wear resistance. For composite manhole covers, a primer is not required; you can apply a special paint directly. Before use, ensure to stir the paint thoroughly. If you are using a two-component paint, mix the components in the recommended proportions and allow the mixture to stand for 10 to 15 minutes to cure before application. Additionally, adjust the paint's viscosity based on the weather conditions by adding a small amount of thinner, ensuring smooth application without sagging.

III. Construct Standardly and Maintain Well

A brush or roller is sufficient for local repair. First, apply the primer and control its thickness properly. After the primer dries to the touch, apply the intermediate coat, and finally the topcoat. Brush each layer evenly without missing any spots or leaving small pinholes. For large-area re-spraying, use a spray gun—keep it 20-30cm away from the manhole cover surface, adjust the pressure appropriately, and apply thin coats 2-3 times. Spraying too thickly at one time may cause the paint film to crack.

Choose a day with a temperature of 5-35℃ and low humidity for construction. Never construct in rain, snow, strong wind, or direct sunlight. After application, cover the manhole cover in a well-ventilated place for more than 7 days—don’t let vehicles crush or people step on it during this period.

IV. Simple Inspection and Subsequent Maintenance

After a repair, check that the coating is smooth, blends seamlessly with the existing coating, and shows no noticeable color differences or defects. Use an instrument to measure the thickness; the total thickness of the three layers should reach between 180 and 250 µm to be considered acceptable. Conduct daily inspections and promptly repair any damaged coatings. For manhole covers located on heavy-duty roads, consider applying an additional layer of wear-resistant varnish. In coastal areas, perform a comprehensive inspection and maintenance every 2-3 years.