Is Secondary Spraying Feasible on The Surface of Old Color Aluminum Plates?

Abstract

Color aluminum plates are widely applied in architectural decoration, industrial equipment, and outdoor engineering due to their excellent corrosion resistance, lightweight properties, and decorative effects. After long-term service, the surface of color aluminum plates often suffers from fading, chalking, minor peeling, and oxidation, which compromises aesthetics and protective performance. Secondary spraying serves as an efficient and cost-effective renovation method for old color aluminum plates. This paper systematically demonstrates the feasibility of secondary spraying on old color aluminum plate surfaces, analyzes key influencing factors including substrate condition, surface pretreatment, coating compatibility, and construction technology, and summarizes standardized construction processes, common technical problems and solutions. The research verifies that qualified secondary spraying can restore the surface performance and decorative effect of old color aluminum plates, providing reliable technical support for the renovation and reuse of color aluminum plate facilities.

1. Introduction

Pre-coated color aluminum plates are factory-finished metal materials with integrated coating and molding. Under long-term exposure to natural environments such as ultraviolet radiation, rain erosion, temperature alternation, and dust pollution, the original surface coating will gradually age, resulting in color fading, surface chalking, local cracking, and slight peeling. For most old color aluminum plate structures and equipment, overall replacement is costly and wasteful of resources. In contrast, secondary surface spraying renovation features low cost, short construction period, and good renovation effect, making it a mainstream technical solution for the renewal of old color aluminum facilities.

However, different from primary factory spraying, secondary spraying on old color aluminum plates faces uncertain risks such as residual aging coatings, surface oxidation layers, and poor adhesion between old and new coatings. Many on-site renovation projects encounter problems like new coating peeling, blistering, and short service life due to non-standard processes. Therefore, clarifying the feasibility boundary and standardized technical process of secondary spraying is crucial to ensure the long-term stability of the renovated coating.

2. Overall Feasibility Analysis of Secondary Spraying

After systematic experimental verification and engineering practice summary, secondary spraying on old color aluminum plate surfaces is technically feasible and economically viable under standardized operation conditions. Its feasibility is mainly reflected in three dimensions: material adaptability, structural stability, and performance restoration.

First, aluminum alloy substrates have stable physical and chemical properties. Long-term service only causes surface coating aging rather than substrate deformation or performance failure. After removing the aging invalid coating and oxide layer, the aluminum substrate can form a stable bonding interface with new coatings, laying a foundation for secondary spraying construction. Second, modern modified acrylic, polyurethane, and fluorocarbon coatings have strong compatibility with traditional color aluminum plate factory coatings. Matching coating systems can effectively avoid chemical rejection and interlayer separation between old and new coatings. Third, qualified secondary spraying construction can make the new coating reach or approach the protective performance and decorative effect of the original factory coating, with outdoor service life up to 5–8 years, which fully meets the actual use needs of engineering projects.

It is worth noting that secondary spraying has applicable boundary conditions. It is not suitable for color aluminum plates with large-area peeling, severe substrate corrosion, bending deformation, and hollow delamination of the original coating. Such damaged substrates need local repair or partial replacement before secondary spraying construction.

3. Key Factors Affecting the Success of Secondary Spraying

Surface Condition of Old Color Aluminum Plates

The aging degree of the original coating is the primary factor determining the spraying effect. For old plates with intact original coating, no peeling, no blistering, and only slight fading and chalking, secondary spraying can be carried out after simple cleaning and polishing. For plates with local cracking, floating powder and minor peeling, partial coating removal and flat polishing are required before construction to eliminate hidden dangers of poor adhesion. For severely aged surfaces with large-area peeling and substrate oxidation and chalking, the residual old coating must be completely removed to ensure the new coating directly bonds to the clean aluminum substrate.

Surface Pretreatment Quality

Thorough surface pretreatment is the core link to ensure the adhesion of secondary spraying coatings, and is also the key to avoid post-construction peeling and blistering. The smooth and non-porous characteristics of aluminum plates make it difficult for coatings to adhere naturally. Residual dust, oil stains, wax layers, oxide films and floating powder on the old surface will directly lead to coating failure.

Standard pretreatment processes include overall cleaning, degreasing, de-chalking, polishing and dust removal. First, use neutral detergent and clean water to remove surface dust and attachments, then use professional metal degreaser to eliminate oil and silicone residues. For oxidized surfaces, fine sandpaper of 180–220 grit is used for overall light polishing to increase surface roughness and enhance coating adhesion. After pretreatment, the surface must be kept dry, clean and rough without any floating ash and oil pollution.

Compatibility of Old and New Coatings

Coating incompatibility is a common cause of secondary spraying failure. Traditional color aluminum plates mostly adopt polyester or fluorocarbon factory coatings. During secondary spraying, low-quality ordinary paint will have chemical reactions with the old coating, resulting in wrinkling, blistering and delamination. Therefore, it is necessary to select matching coating systems according to the type of the original coating. Polyurethane and modified acrylic coatings are suitable for most polyester color aluminum plate renovations, while fluorocarbon finish paint is preferred for high-standard fluorocarbon color aluminum plate renewal to ensure consistent performance and good interlayer bonding force.

Construction Environment and Process Parameters

Secondary spraying has stricter environmental requirements than primary spraying. Construction is prohibited in high humidity, rainy, dusty and strong wind environments. The optimal construction temperature is 15–35℃, and the relative humidity is controlled below 85%. In addition, the spraying thickness, gun distance, spraying speed and curing time need to be strictly standardized. Excessively thin coating leads to poor covering power and insufficient protection, while excessively thick coating causes sagging and cracking; unreasonable gun distance will result in uneven coating and reduced adhesion.

4. Standardized Secondary Spraying Construction Process

To ensure the stable quality of secondary spraying on old color aluminum plates, the construction shall be carried out in strict accordance with the standardized process flow: surface inspection and judgment → partial old coating removal → overall cleaning and degreasing → surface polishing and roughening → dust removal and drying → primer spraying → curing treatment → finish spraying → surface inspection and maintenance.

First, conduct a comprehensive inspection of the old color aluminum plate surface to distinguish the aging degree and mark severely damaged areas for local polishing and coating removal. Then complete overall degreasing and cleaning, and polish the whole surface to form a uniform rough base surface. After the surface is completely dry and dust-free, spray a special metal etching primer. The primer can penetrate and bond with the aluminum substrate and old coating effectively, improving the adhesion of the finish coat. After the primer is fully cured, spray the finish paint in layers, with uniform thickness and no missing spraying or sagging. Finally, complete natural curing, and conduct adhesion test and flatness inspection after construction. The qualified coating adhesion shall reach Grade 1 or above by the cross-cut method, with no cracks and peeling after 50cm impact test.

5. Common Problems and Countermeasures in Secondary Spraying

New Coating Peeling and Delamination

This problem is mainly caused by incomplete surface degreasing, insufficient polishing, and residual floating powder on the old surface. The solution is to strengthen pretreatment, thoroughly remove surface oil and oxide layers, and ensure uniform surface roughness. For partially peeled coatings, remove all loose old coatings and repair the substrate before re-spraying.

Surface Blistering and Wrinkling

Blistering and wrinkling mostly occur due to coating incompatibility, excessive coating thickness, or construction in high humidity environment. During construction, matching coatings must be selected according to the original coating type, the coating thickness must be controlled reasonably, and construction must be avoided in humid and rainy weather. Local blistering parts need to be polished and repaired in time.

Uneven Color and Fading Quickly

Uneven color is caused by uneven spraying thickness and inconsistent paint dilution ratio; rapid fading is due to the use of low-quality coatings with poor ultraviolet resistance. The countermeasure is to strictly control the paint proportion and spraying process, select high weather resistance coatings matching the original color, and ensure uniform and consistent finish color.

6. Economic and Environmental Value of Secondary Spraying

Compared with the overall replacement of color aluminum plates, secondary spraying renovation has significant economic and environmental advantages. The renovation cost of secondary spraying is only 20%–30% of the replacement cost, which greatly reduces the engineering investment. Meanwhile, it avoids the waste of metal resources caused by scrapping old aluminum plates, reduces the discharge of construction waste, and conforms to the concept of energy conservation and emission reduction. In addition, the secondary spraying construction period is short, which can minimize the impact on the normal use of buildings and equipment, with high engineering practical value.

7. Conclusion

Secondary spraying on the surface of old color aluminum plates is completely feasible in engineering applications, and the renovated coating can achieve stable protective performance and good decorative effect. The key to successful secondary spraying lies in accurate judgment of the old substrate condition, standardized surface pretreatment, reasonable matching of new and old coatings, and strict control of construction processes. For old color aluminum plates without severe substrate damage, secondary spraying is an efficient, economical and environmentally friendly renovation scheme. With the continuous upgrading of coating materials and construction technologies, secondary spraying technology will be more widely used in the renovation of architectural exterior walls, industrial equipment and outdoor color aluminum facilities, providing strong support for the long-term service and sustainable utilization of metal decorative materials.