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Prepainted Steel Basics

From roofing panels to car doors, prepainted steel has a myriad of uses due to its success across multiple industries and minimal maintenance requirements.

But if you stop to think about it, how much do you really know about the ins-and-outs of prepainted metal?

For example, do you know that there’s more than aesthetics at play when we’re talking about why we paint?

Or how about the paint types that are best for your end use application depending on different environmental factors?

In this article, we’re going back to the basics with an introduction to prepainted steel. By the end, you’ll have a clear understanding of prepaint, and you’ll be able to download an easy-to-follow, printable guide covering the main points we’ve discussed below.

Why Do We Paint?

Aside from adding aesthetic value, there are two other reasons why we paint:

1. To provide protection

2. To decrease energy costs

How Paints Provide Protection

Galvinfo notes that paints provide protection, thus improving product life because they act as a barrier between the coating and corrosion-inducing agents like moisture and oxygen. Secondly, most paints contain specific corrosion-inhibiting agents, making them even more useful in the fight against rust.

You might be thinking: if paint acts the same as a protective coating, is it okay for me to paint uncoated steel, save some money and still get the same level of protection?

Not so fast.

While paint does act as a barrier film, that doesn’t mean it’s impervious to moisture. “Water can penetrate the paint, and reach the metallic coating if the panels are wet for long periods,” says GalvInfo. “For this reason, the barrier aspect of the paint alone is not sufficient.”

In other words, without a coating like zinc (galvanized and Galvalume are common base layers), the underlying steel is subject to corrosion if the paint is blistered or damaged.

How Paints Decrease Energy Costs

It seems counterintuitive that adding another step to the processing chain would decrease energy costs, but in fact, prepainted steel in roofing applications can save a household up to 40% of its annual energy cost.

Depending on your geographical location, installing reflective roofing (white is common) can keep your home cooler, reducing the strain on your bank account.

Even more, painted roofing can also reduce urban air temperatures by as much as 12 degrees Fahrenheit, according to research from the Metal Roofing Alliance.

What are some typical coil paint types?

1. Polyester

2. Silicone polyester

3. 70% PVDF fluoropolymers (Kynar)

Here’s a breakdown of each paint type:

1. Polyester is known as the most economical paint system because it has the lowest cost, buyers should know that it also has a very limited warranty. Polyester might be used in the metal building or roofing industry as a liner panel (wall panel) on the interior of a building.

2. If you’re looking for durability and aesthetic appeal, a silicone polyester could be what you need. It’s a close second to the Kynar system, though it’s formulated differently.

Silicone polyester combines the durable characteristics of ceramics and other inorganic pigments with the strength of a unique silicone polyester resin. It will take the abuse of anything that’s thrown its way in the case of extreme weather conditions and environments while still maintaining a polished finish.

3. In the coil world, Kynar coatings are the premier coating system choice and can be applied to aluminum, galvanized and Galvalume. A two-coat application for commercial, residential and pre-engineered buildings and roofing, it offers excellent UV protection, chalk/fade resistance, high film integrity with superior adhesion and flexible post-roll forming.

Additionally, Kynar is available in energy efficient and solar reflective.

Which resins are best?

Best = Fluoropolmers (Kynar) – color

Better = Silicone Polyester – color

Good = Polyester (color)/Acrylic (clear coating) – good for initial coating against resistance

The best and most common for external building and roofing applications are Kynar and silicone polyester paint systems due to their warranties and overall durability.

However, if you’re looking for a paint system for indoor use, the lower cost of a polyester could work well for you.

What Environmental Factors Influence How Many Coats of Paint I Should Use?

While it’s impossible to list all of the environmental factors responsible for paint wear, GalvInfo lists common ones such as:

– Acid rain

– Coastal salts

– Wetness of the environment

– Exposure to ultraviolet light

The impact these factors have on paint integrity really depends on the paint systems. While Kynar is superior in this area, all warranties are different.

To ensure compatibility, you should check with the manufacturer for specifics on your end use application and needs.

Should I be using Galvalume or galvanized?

The short answer: it doesn’t really matter. Instead, it’s more important that you pay attention to the integrity of the paint system.

Why?

Because prepainted Galvalume and galvanized life is dictated by the performance or the appearance of the paint.

These factors affect paint integrity:

Fading: paint lightens over time. Depending on the paint system you use and the environmental factors we discussed above, you can expect some paints to fade faster than others.

Chalking: chalking is another way to say powdering. While all paints chalk to some degree, a paint in a higher quality paint system will resist chalking more effectively as it erodes.

Peeling: when paint fails to properly adhere, it begins the process of peeling away from the surface of the coated steel.

Again – and we can’t reiterate this enough – the higher the paint system integrity, the longer the paint will resist fading, peeling and chalking.

To download a visual PDF guide of this presentation, click here.

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