1.Why can't we just spray paint directly?
Low surface energy: The surface of pre-coated steel sheets is very smooth, especially the PVDF (fluorocarbon) coating, which has very low surface energy, making it difficult for new paint to penetrate and form an effective bond.
Presence of a contamination layer: Over long-term use, dust, oil, aging pigments, oxides, etc., will accumulate on the surface of pre-coated steel sheets. These will form a barrier between the old and new coatings.
2.How to conduct a comprehensive inspection and evaluation before painting?
Inspect the condition of the existing coating: check for severe chalking, corrosion, cracking, or blistering.
If the substrate is extensively corroded or the coating is severely damaged, it is recommended to replace the substrate rather than refurbish it, as the results of refurbishment cannot be guaranteed and the cost may be higher.
3.How to do a thorough cleaning?
Objective: To remove all dust, grease, salt, and other contaminants.
Method:
Perform a preliminary rinse using a high-pressure water gun.
Use a neutral or alkaline cleaner with a brush or sponge for scrubbing. Do not use strong acids, strong alkalis, or organic solvents, as they will severely damage the original coating.
Rinse thoroughly with clean water, ensuring no cleaner residue remains.
Allow the substrate to dry completely.
4.How to choose the right paint?
Compatibility: The newly selected topcoat must be compatible with the old coating and bond well with the primer. It is best to consult the paint supplier.
Recommended Types:
Acrylic Polyurethane Topcoat: Good weather resistance, gloss and color retention; a common renovation choice.
Fluorocarbon Topcoat: High-performance option with excellent weather resistance, but higher cost.
Epoxy or Polyurethane Primer: If a primer is required, choose a type with strong adhesion.
Important: Perform a small-area test spray and allow it to dry completely. Conduct an adhesion test (e.g., cross-cut test) to confirm adhesion before applying to a larger area.
5.What are the risks and precautions?
Adhesion failure: This is the biggest risk. Incomplete surface preparation is the main cause.
Poor appearance: Defects such as orange peel, runs, and uneven coloring may occur, affecting aesthetics.
Poor durability: If the renovation process is improper or the wrong paint is chosen, the lifespan of the new coating will be far shorter than expected, and problems may appear after one or two years.
Cost issues: Professional surface preparation, high-quality paint, and labor costs are not low. If the renovation area is large, a comprehensive cost-benefit assessment of renovation versus replacing the entire panel is necessary.
Health and safety: During spraying operations, masks, goggles, and other protective equipment must be worn, and good ventilation in the workplace must be ensured.