Construction Process of Fluorocarbon Paint Coating for Curtain Wall Metal Structures

With the rapid development of urban construction, various curtain wall materials are widely used in architectural decoration due to their diverse shapes and strong modern feel. Most curtain wall shape designs use aluminum profiles, metal profiles, etc., as supporting frameworks. Since metal materials are prone to rust in air or humid environments, it can greatly affect the safety of components. Additionally, many curtain wall designs require the framework to be exposed, which imposes strict aesthetic requirements. Therefore, choosing suitable anti-corrosion and decorative coatings is very important. In recent years, fluorocarbon paint has been widely used in curtain wall construction as a protective and decorative material for metal structures due to its excellent weather resistance, durability, corrosion resistance, heat resistance, and low-temperature resistance.

I. Construction Process

Process flow: Metal structure substrate treatment → Apply two coats of epoxy zinc-rich primer → Apply two coats of special putty → Apply two coats of sealing primer → Apply two coats of fluorocarbon topcoat.

(1) Metal Structure Substrate Treatment

The surface of metal components may have attachments such as oxide skin, rust layers, oil stains, welding scars, splashes, and burrs. If not thoroughly removed, it can cause the paint layer to blister and peel, directly affecting the adhesion and corrosion resistance of the coating, reducing the service life and decorative effect of the paint film. Before spraying the primer, the surface must be clean, smooth, and free of obvious pits and damage, revealing the metallic luster.

Use sandblasting for rust removal, achieving a rust removal grade of Sa2.5, with a surface roughness maintained at 40~70μm. Before coating, smooth and round the weld seams, and ensure the substrate is dry and clean.

(2) Apply Epoxy Zinc-Rich Primer

In the anti-corrosion coating system for steel structures, the role of the anti-rust primer is crucial. It must have good adhesion to steel and provide excellent rust prevention. This project uses the Bermuda brand epoxy zinc-rich primer, which is a two-component coating made of epoxy resin, zinc powder, and polyamide resin, with good construction performance and excellent corrosion resistance and wear resistance.

Before spraying, ensure that the substrate is free of oil stains, dust, water, acids, and alkalis. Properly protect the surrounding area of the work surface to be sprayed.

The primer is a two-component system, mixed in a ratio of A:B=9:1, and must be stirred evenly according to regulations before use. Surface dry time is 0.5 hours, and full dry time is 48 hours.

Use an airless spraying method for construction, applying two coats with a 24-hour interval, and the dry film thickness should not be less than 75μm. This spraying method reduces paint mist and allows for variable film thickness, ensuring even spraying and high production efficiency.

(3) Apply Special Putty

Use fluorocarbon paint for surface decoration, which has strict requirements for the flatness of the substrate. To meet these requirements, apply two coats of Lao Shan Yang brand atomized gray putty.

Mix the putty in a ratio of 100:2 for the main agent and curing agent, ensuring a uniform color. The mixed putty must be used within 7-10 minutes (the usable time is affected by temperature and humidity).

Use a scraper to apply the putty in layers. After each layer is applied, wait for it to fully harden before sanding the surface with 240-grit sandpaper to remove the edges created by the scraper. After the final layer of putty is applied, sand with 360-grit sandpaper to avoid surface patterns.

The thickness of the putty should not exceed 0.5 mm, or it may shrink and crack. If filling uneven areas, multiple applications may be necessary, allowing each layer to dry thoroughly before applying the next.

The surface layer should be finely sanded, smooth, shiny, and free of capillary pores, with no obvious bumps or depressions under light.

(4) Apply Two Coats of Sealing Primer

The sealing primer selected is Bermuda brand epoxy iron oxide intermediate paint, mixed in a two-component ratio of A:B=100:15, stirred evenly before use, with a surface dry time of 0.5 hours and full dry time of 24 hours. This product has good permeability resistance, weather resistance, and good interlayer adhesion.

Use air spraying to apply two coats of sealing primer. After properly protecting the surrounding area of the work surface, spray evenly with a spray gun. The interval time between coats is 24 hours, and the dry film thickness is 60μm. The air compressor pressure is 2-4 kg/cm², and the distance from the nozzle to the object being coated is 20-40 cm. The skill level of the operator determines the quality of the spray paint.

(5) Apply Fluorocarbon Topcoat

The topcoat uses the YUGONG brand fluorocarbon metal paint, which has excellent weather resistance, outstanding physical and mechanical properties, excellent resistance to wet and dry alternation, and superior alkali resistance and rust prevention compared to general acrylic polyurethane topcoats. This product has good construction performance and can adapt to various application methods, such as brushing, rolling, and air spraying.

After the iron oxide intermediate paint dries, spray the first coat of fluorocarbon topcoat, touch up any defects, spray the second coat of fluorocarbon topcoat, check and touch up, and then spray the fluorocarbon topcoat. Use air spraying for the topcoat, with a 24-hour interval between coats and a dry film thickness of 50μm.

When spraying, use a dedicated spray gun to continuously and evenly spray the mixed topcoat until the color is uniform and the film is full. Stir the fluorocarbon paint regularly to ensure an even coating. On-site mixing should be done as needed to avoid waste. The interval time for fluorocarbon topcoat can be shortened with increased temperature, enhanced ventilation, and the addition of curing agents. During construction and drying, the relative humidity should not exceed 80%, or it may cause severe bubbling in the paint film.

II. Quality Control Measures for Common Issues

(1) Dripping, cracking, uneven treatment of weld seams, and joint issues.

The main reason is due to excessive coating thickness, overlapping coatings, and uneven depth of the topcoat; the large spacing makes continuous construction impossible. The following measures can be taken: do not make each layer too thick, and ensure that the edges of the object, rivets, welds, bolts, etc., which lack adhesion or are difficult to form an effective coating, are adequately coated after scraping the putty.

When spraying, the working surface should be divided into sections, and multiple people should work together to prevent leaving spray joint marks. If a joint must be left, it should be at the corners or on the dividing lines. It is best to complete the construction in one go without repairs to avoid joint issues.

(2) Color difference phenomenon

The main reason is the lack of bulk purchasing of raw materials; mixing different coatings; and not stirring according to construction requirements. The following measures should be taken: procure engineering materials in bulk, strengthen incoming testing to ensure color consistency. Strictly control the construction process, prohibit mixing different colored coatings for spraying; before construction, evenly stir the raw materials, and assign a dedicated person to deliver the uniformly mixed materials to the spraying workers in a timely manner.

(3) Fluorocarbon paint blooming phenomenon

The main reason is unstable control of the spray gun's paint output, which varies; uneven spraying; significant differences in the skill levels of construction personnel; and the influence of weather, temperature, and humidity during construction.

During spraying, two people need to cooperate, with one responsible for spraying and the assistant responsible for masking and supplying materials. The spray gun operator should maintain a distance of about 25 centimeters from the working surface and keep it perpendicular. When spraying, avoid diagonal spraying and repeated spraying, and keep an eye on the already sprayed areas, adjusting the speed of the spray gun, the size of the nozzle, and the air pump pressure as needed to ensure adequate atomization of the coating.

The construction temperature during spraying should be between 5℃ and 40℃, with relative humidity ≤ 80%. Construction is not allowed in rainy, foggy, frosty, snowy, or windy weather.

3. Quality standards

The surface should have consistent color, be smooth and flat, with uniform thickness, and be free from issues such as missed spraying, joints, transparency, sagging, and blooming.