Brush coating construction method

Brush coating is mainly used for pre coating and touch up coating. Before large-scale spraying, in order to ensure the quality of the project, all corners and other areas that are not easy to spray should be pre coated to ensure sufficient film thickness.

When brushing, soak the paint brush into about 1/2 of the material bucket and lift it up. Gently tap the edge of the bucket a few times to remove excess paint, and then brush. When brushing, follow the steps of coating, wiping cloth, and correction. When painting vertical surfaces, the last coat should be applied in the direction of light, and the film thickness should be uniform to prevent sagging, wrinkling, and missed coating.

Before applying anti-corrosion coating, it should be thoroughly stirred evenly. If it is too thick for construction, it can be diluted with a diluent (not more than 5%) appropriately.

Generally, anti-corrosion coatings should be applied in layers, with an interval of more than 24 hours between each coat. Special coatings should be applied according to the instructions.

The anti-corrosion topcoat is applied uniformly and of consistent color after the anti-corrosion primer coating has dried.

Air spraying method

High pressure airless spraying is used for the final anti-corrosion coating of large-area components during the prefabrication process.

Equipment: Air compressor 6m3/min; Drive high-pressure pumps, high-pressure spray guns, etc.

Spray pressure: Compressed air 0.4-0.6MPa; High pressure pump at around 15MPa.

The various parameters during spraying are as follows: the distance between the nozzle and the object surface is kept at an appropriate minimum distance, and the amplitude of the jet is: spraying large-area objects is about 40-50 cm; spraying large-area objects is about 30-40 cm; spraying small-sized objects is about 20-30 cm.

Coating: After passing the trial spraying, large-scale spraying should be carried out.

Attention: When spraying, the air pressure should be stable, and the nozzle should be perpendicular to the sprayed surface. The speed of the spray gun should be balanced, the coating thickness should be uniform and meet the design requirements, and there should be no defects such as sagging, missed spraying, dry spraying, cracking, etc.

Coating requirements: The coating used meets the design requirements and has a product qualification certificate. Filter with a sieve if necessary. When configuring, pay attention to the curing period and mixing period of the paint, achieve on-site preparation and use, and avoid wasting paint.

After coating, immediately clean the equipment with solvent and discharge the remaining paint from the spray gun. Inhale the solvent for thorough cleaning, remove the high-pressure pipe, and blow off the solvent inside the pipe with compressed air.

To prevent the treated metal surface from rusting again, the first layer of anti-corrosion primer should be applied in a timely manner, and the brushing should be completed within 6 hours at the latest (if exceeded, secondary sandblasting should be carried out), so that the coating has good adhesion and density.

The welding seam of the bridge deck within the range of 50-100mm shall not be coated with primer temporarily. Before each layer of paint is applied in the future, an additional 50mm shall be left at the edge of the welding seam to form a stepped protective layer.

During the construction process, measure with a wet film card to achieve the required thickness, without any defects such as sagging or leakage of the paint film. If it is not qualified, mark the defective area and apply touch up paint.

After the coating surface is dry and checked for any brush coating defects, the intermediate coating can be applied. The operating points are the same as above.

The painting construction conditions should be carried out within the corresponding temperature range according to the product manual. When the temperature exceeds or falls below the specified temperature range of the product or the humidity and dew point temperature do not meet the requirements, the operation should be stopped.

The next coat of paint can only be applied after the previous coat has dried. If there is a 7-day interval between the two topcoats, they need to be sanded with fine sandpaper to create a fine surface.

Secondary coating, surface treatment, and repair

The surface of the secondary coating should meet the requirements of the next coating.  

Before on-site painting, the surface of the painted parts should be thoroughly cleaned of oil, mud, dust, and other contaminants. Generally, methods such as water flushing, cloth wiping, or solvent cleaning can be used.

After surface cleaning, use tools such as wire brushes to roughen the original paint film and protect the component numbers.  

Clean the surface with oil-free and waterless compressed air.

Before the secondary coating, the defective parts of the previous coatings should be repaired.

When repairing the coating, if defects are found during installation inspection, they should be repaired according to the original coating design. After installation, the following parts should be repaired: A) exposed parts of the joint and fasteners, etc; B) Welding and burnt parts during installation; C) Component number and areas of omission; D) The damaged area during installation.