Paint coating of is the widespread corrosion protection method metal structures due to its cost effectiveness and easy application.
Metal is a durable material and its versatile nature makes it a popular choice for multiple applications, however, the main pitfall of a metal fabrications is its vulnerability to moisture.
Corrosion can turn a solid metal into rust, therefore, it requires a good protection. The most popular protection is the application of wet paints to the metal surface. Wet painting not only protects the steel but also provides visual finishing options for steel buildings.
2. Types of Paints
Alkyd paints are a type of oil based paint. They can be used as a primer, undercoat and topcoat. They are popular inexpensive paints which are often chosen when a high gloss, versatility and moderate protection is required.
Alkyd paints do not preserve the colour for a long time. They also do not adhere well to galvanized surfaces. Due to binder content in alkyd paints, it is very resistant to damage.
One essential feature to note about alkyd paints is that they dry slower than other paints, therefore, it is important to consider the drying period during planning.
Acrylics are among the most popular and widely used water or solvent based coatings. Acrylic paints offer excellent colour and gloss retention as well as excellent durability and good adhesion to a large number of substrates. Their outstanding colour retention makes them very popular for applications where long lasting colour protection is requires such as architectural and outdoor applications.
Acrylic paint is also very durable and can withstand wear and tear but they are more expensive than the alkyd paints.
Epoxy coatings are two-component paints that a mixed with a hardener to offer better corrosion protection than alkyd paints. They are widely used in moderate corrosive environments in industrial applications. They also offer strong heat resistance to components, with effective adherence to steel surfaces.
Epoxy paints do not preserve the colour for a long time, therefore, a polyurethane top coat is usually offered as a top coat over epoxy primer and middle coat.
Epoxy paints are also more costly than the alkyd based paints.
Zinc rich primers provide the highest order of protection of all prefabrication primers. The zinc primer protects the steel surface by corroding sacrificially in preference to the steel. They are popular for applications in marine and corrosive industrial environments. Zinc primers are common when hot dip galvanization is not possible. They are applied in the workshop and subject to cracking if applied too thick.
Polyurethanes are known for their outstanding chemical resistance, very good clarity, high gloss, and very good mechanical properties including hardness, flexibility and abrasion resistance. They are often used as a top coat to epoxy paints thanks to their colour pretention and high gloss characteristics.
There are multiple paint coating options for metal surfaces all with different level of protection, finish options and application requirements. The common prerequisite for all paints is a proper surface protection prior to painting. Generally, the better the corrosion protection the higher the paint cost.
Last but not least, apart from the paint type, applied paint thickness is essential to determine the appropriate paint coating system.