You are not limited in your choice of color for your steel wall and roof panels. The choice of color, texture and pattern are almost endless with today’s metal panel finishing options. But before you make any decisions about new panels or refinishing existing panels, educate yourself about the various coatings and paint you will hear about on your search.
To begin with, all steel leaves the mill with an anti-corrosive coating.
- Galvanization is the application of a zinc coating to the exterior of a steel member to prevent rust. Most steel is galvanized using a hot dip process in which the steel is placed in a bath of molten zinc.
- Galvalume (R) is a trademarked mixture of 45% zinc and 55% aluminum that is applied to steel to prevent rusting. Galvalume has a fine crystalline appearance smoother than that of galvanized steel and is more corrosion-resistant than galvanized steel. However, cut edges and scratches are less protected.
- Galfan(R) is licensed by GTS at the University of Pittsburgh. It contains 95% zinc and 5% aluminum typically applied in a hot dip process. Galfan has superior durability against cracking or flaking.
The cost of galvanized steel and Galvalume coated steel are about the same but knowing the difference can help you determine the better choice for your needs. Also, if the coating is penetrated by scratching or cutting, the raw edges and scratched areas are no longer protected.
THE CHEMISTRY BEHIND PAINT COATINGS
Paint coatings are created from a variety of material, but the most common are acrylic and polyester. Paint provides secondary protection over and above (literally) the anti-corrosive finish steel always has.
Acrylic and polyester-based paints are synthetic polymers. These polymers are highly durable and abrasion-resistant. They also have excellent stretch and recovery, an important detail to cope with the thermal movement of metal.
Other paints are fluorocarbon-based with a polyvinylidene fluoride resin (PVDF) or fluorinated ethylene vinyl ether (FEVE), an extremely stable compound with high durability, color stability and UV resistance. It is also highly resistant to heat and chalking.
- Polyester and acrylic based paints typically come with a three to five-year warranty. For paint applied by the manufacturer, maintenance repair coatings should be planned within the first five years.
- Siliconized polyester paint has 10 to 20-year warranties and resists chalking and retains gloss well.
- Fluorocarbon-based PVDF or FEVE coatings are sold under the trade names Kynar 500 or Hylar 5000 and are warrantied for 20 years. Fluorocarbon-based paint is 70% resin with 30% pigments and solvents, and withstands sunny and salty environments better than the typical polyester coating.
Polyesters come in a wide range of color and gloss. They resist marring, solvents, staining and corrosion. However, they are not very durable as evidenced by the short warranties provided by manufacturers. Polyesters are often used on elements such as doors that are easily repainted.
Silicone-modified polyesters (polysiloxanes) are a hybrid technology that combines organic and inorganic material that results in higher durability than simple polyester. Pre-engineered buildings are often coated with silicone-modified polyesters.
Polyurethanes cure by chemical reaction and are applied as two components — resin and curing agent — which are combined at the time of application. It creates a hard, dense film and has good chemical resistance. Aliphatic polyurethane resists weathering well.
Polyaspartics are modified polyureas that perform similarly to polyurethanes. They have an increased application thickness compared to polyurethanes and often require an epoxy primer when applied to galvanized surfaces.
Acrylics are highly durable but less elastic than polyesters and may crack and peel with thermal movement. Epoxies are used in high-corrosion or salt-air environments but tend to chalk with outdoor exposure.
Fluoropolymers with PDVF or FEVE resins are the most durable coatings you can get. They can be used in coil applications without fear of peeling or cracking. They are often used in metal roofing, cladding and curtain wall panels.
Also, they retain their color and gloss well, as mentioned above. Coatings are available that are only 50% resin, but they do not perform as well. PDVF coatings are baked onto the surface at the factory while FEVE is more often used in field-applied fluoropolymers.
Some colors and coatings are used for specific purposes beyond the aesthetic and durable.
One example is a cool roof, an element of energy efficient construction.
- A cool roof is coated with a white or light colored paint.
- White roofs reflect a significant percentage of solar radiation away from the roof.
- Reflective pigments added to the paint re-emit any heat absorbed by the roof.
Another example is intumescent coatings, otherwise known as fire-protective paint.
- Intumescent coatings expand rapidly in the presence of fire and absorb the heat, deflecting it away from the substrate.
- It develops a char layer to insulate the substrate and delay failure of the structural elements.
- Fire-protective coatings are termed fire retardant or fire-resistant. Fire-retardant indicates the product is tested to the ASTM E-84 method addressing flam spread and smoke development. Fire-resistant indicates testing to ASTM E-119, which involves testing over two to four hours to verify extended protection.
Class A fire-protective coatings comply with the most stringent standards.
Environmental compliance has come to the forefront in recent years. Coating manufacturers have developed lines of water-based, low-VOC (Volatile Organic Chemical) coating solutions. The main worry is whether a water-based coating can perform as well as a solvent-based epoxy.
New technology solved the performance issue in the latest epoxy systems (Type 5). A proprietary, non-ionic surfactant added to the epoxy resin pre-reacts with the resin and a hydrophobic amine adduct curing agent. The mixture results in a hydrophobic binder system with improved film formation.
The new formulation is highly corrosion-resistant, and the coating dries quickly.
Today’s finishes and coatings for metal are available in a wide range of colors. Manufacturers typically stock panels in popular colors but you can custom-order any tint or hue you need to match the surrounding buildings, meet corporate color standards or add the exact pop of color you need for your building to stand out.
Your finishing options include factory applied coating and field-applied coating to use for maintenance and repair. Apply the coating according to the manufacturer’s instructions to optimize performance.
Paint and coatings not only add to the aesthetics of your structure, but some also have specialized applications to create cool roofs or fire-protective coatings.
As always, you can consult your metal building manufacturer to obtain more information and discuss all the options.