Painting Metals
Spray painting a galvanized product is an effective and relatively simple operation, especially when the coating is properly sealed immediately after metallization.
Why intervene on a spray galvanized one?
Spray-applied zinc coating normally has a porosity of 8–10%. This characteristic makes the use of specific sealants, capaci di penetrare nei pori e migliorare sia la protezione anticorrosiva sia l’aspetto finale della superficie.
Correct sealing reduces the area of the cladding exposed to external agents, rallenta la velocità di dissoluzione dello zinco, migliora l’uniformità superficiale e limita il trattenimento di sporcizia e inquinanti.
Advantages of sealants
- They penetrate the pores of the coating and improve its protection.
- They reduce the area exposed to aggressive agents.
- They slow down the dissolution of zinc.
- They smooth the surface, improving the aesthetic result.
- They prevent the accumulation of dirt and pollutants.
- They facilitate the movement of the product.
- They can be pigmented to achieve a nicer finish.
Required features
- Low viscosity (less than 3 poise).
- Medium leafing power.
- Low water absorption.
- Resistance to chemical attacks.
- High ability to penetrate pores.
When to apply the sealant
The sealant must be applied immediately after spraying the zinc, in modo da evitare contaminazioni o inquinamenti della superficie che potrebbero compromettere la qualità del trattamento successivo.
Sealants and paints: the difference
It is important to distinguish between sealant and paint.
The paint settles on top of the metal surface forming a surface layer, while the sealant, thanks to its low viscosity, penetrates the pores del rivestimento e li chiude senza aggiungere spessore significativo.
Why seal before painting
Before painting a spray galvanized product it is advisable to apply a sealant. In the absence of this treatment, many paint binders can penetrate the pores of the coating, leaving scattered and poorly anchored pigments on the surface.
Commonly used products
First poly
Often applied before painting to improve adhesion of the subsequent cycle.
Phenolic resin
Valid alternative as a preliminary or supplementary treatment depending on the expected cycle.
Vinyl polymers
Used for their compatibility with metallized surfaces and good protective capacity.
Epoxy phenols
Technical solution indicated in cycles where greater chemical resistance and adhesion is required.
Compatibility and precautions
The choice of paint must be made carefully, always checking the compatibility with zinc. Una vernice non idonea può reagire con il rivestimento formando composti all’interfaccia che compromettono l’ancoraggio e la durata del sistema protettivo.
It is essential to avoid alkaline products, poiché gli alcali possono danneggiare il rivestimento e ridurre l’efficacia della protezione anticorrosiva.