When compared to other materials used in the roofing industry, like asphalt, tile, or cement, metal roofing has considerable advantages. In addition to lasting decades longer than other materials, metal panel systems have become even more affordable and practical for both commercial and residential uses. One of the most attractive characteristics is the versatility of colors that metal offers, which is why having the option to choose from a variety of different paint colors and finishes is so important.
Sheffield Metals is an industry leader in the distribution of metal coil and bare metal products used for roofing and wall systems. Before you make the decision to purchase that metal roof or wall system you’ve been looking at, we want to help familiarize you with how different paint systems will perform, especially in regards to chalking and fading, depending upon the elements they are exposed to.
In this article, we hope to give you a better understanding of:
- What the terms chalking and fading mean
- How different paint systems can help protect the metal
- How different environments affect chalk and fade
- What goes in to the testing of different paint systems
What is Fading on Metal Roofing?
One of the most frequently asked questions in the metal roofing industry is: Will my metal roof fade?
The answer is yes.
Fading on painted metal roofing or walls occurs when substances like water, pollution, and chemicals in the atmosphere and specific environments react with the pigment of the paint. In other words, the pigment begins to break down, which causes the color change. This change usually lightens the color, but it has been known to darken or completely change specific colors. Also, it’s important to note that panels on the same structure may not even fade uniformly, as every portion is not always subject to the same elements.
No matter what type of pigment or resin that a manufacturer uses on a coil, nothing will preserve the color forever when the panels are in an outdoor environment. Like we discussed in our explanation of metal roof warranties, the best way to imagine what fading on metal will look like is to compare it to how a piece of clothing might fade its color over time. Even though the color fades because of regular wearing and washing, it doesn’t take away it from how well it wears, or in a metal panel’s case, it doesn’t take away from how well it protects your structure.
That being said, there are ways to prolong the life of the color of your metal roof, and it starts with being educated and informed about the factors that affect fading, the types of resins and how well they stand up to the elements, and how fading is actually measured.
Factors Affecting Metal Roof Fading
- UV or sun exposure – Probably the biggest determining factor in how a metal roof or wall panel system will fade is based on the amount and strength of the UV exposure the panel gets. For example, a metal roof in Texas is more susceptible to fading due to sun exposure than a metal roof in Wisconsin. This is the reason that most paint systems are often tested in locations with extreme weather, like Florida, to see how it measures up to the conditions over a long period of time.
- Temperature – While any temperature will cause fading to happen over time, extreme heat and cold speed up color changes. Research and field testing also shows that frequent temperature fluctuations weaken the pigment by manipulating the color’s chemical makeup.
- Moisture – Any kind of moisture, whether it be rain, snow, seawater, condensation, etc., will alter the makeup of any substance over time. Resins are designed to stand up to water and protect the pigment, but constant exposure to water, especially standing water, speeds up the process. Acid rain or water exposed to harsh pollutants in the air that come into contact with the panels can affect fading too. Be aware that many warranties don’t cover metal roofing on a structure that is within a certain distance of a coastline, bay, or marsh. If you’re unsure if moisture will affect your metal roof or wall system, ask the manufacturer before you buy.
- Pigment – There are two different types of pigments used in the paint that goes on a metal coil:
- Organic – A natural pigment made up of petroleum compounds that is carbon-based and more susceptible to color fading. Most vivid, rich, and bright colors are made up of organic pigments.
- Inorganic (ceramic) – Pigment that is created from mineral compounds, mostly metal oxides. Since these are engineered to perform up to high standards, paint with this kind of pigment resists against fading much longer than organic pigments. These colors are earth tones, including browns, greens, and beiges.
- Resin – Pigment makes up the color in a paint system, but the resin is the ingredient that protects and preserves the color and provides added durability. Resins also bind the paint system to the substrate metal it’s applied to.
Types of Resins Used for Metal Roofing
The resins used in paint systems make all the difference when it comes to the longevity of the color on a metal coil or panel. While these names are very technical, think of these as “Good, Better, Best” classifications to help you determine what resin will work best in the environment you live:
- Polyvinylidene fluoride (PVDF) – This resin is made up of about 70% PVDF and 30% acrylic. Commonly referred to as Kynar 500® or Hylar 5000®, PVDF resins are the best protective coatings available to stand up to extreme temperatures, sun exposure, oxygen, humidity, and even pollution particles in the atmosphere. Coils made with this resin are most likely to have the longest chalk and fade warranties—typically up to 40 years, but are slightly more expensive due to superior durability.
- Silicone-modified polyester (SMP) – SMP coatings are a step below PVDF in terms of quality and warranty options. These consist of a combination mixture of polyester and silicone materials. SMPs have been known to be a great option to defend against extreme weather conditions, while still carrying up to 35 years of paint warranty options.
- Fluoroethylene vinyl ether (FEVE) – FEVE resins are made up of various vinyl ether and fluoro-olefin units, which act as good protectants against oxygen, water, and chloride, but can degrade quicker in environments with high UV exposure. FEVE resins are popular because of their strong bonding properties to different types of metal roof materials.
- Plastisol – Plastisol resin is made up of plasticized vinyl and is generally applied to a metal coil that will be used in a very corrosive or intense environment. Plastisol will protect against degradation from the weather, but be aware that this resin has been known to change the pigment of bright and vibrant colors.
- Polyester – While polyester, a synthetic polymer, is not the top performing resin to use on a metal roof or wall panel to protect against fading, it does come at a lower price point. There are still warranties offered on polyester coated coils, but chalk and fade are typically only covered for a maximum of 10 years.
Measuring Metal Panel Fading
The standard for measuring the fade on a metal panel is determined using Hunter Lab’s Delta E (∆E) unit, according to ASTM International standard D-2244. The number that represents “E” in ∆E is the difference between a sample of the paint and the paint’s original color. For example, if a sample comes in at ∆3, it means the color has changed three Hunter Delta E units from the original. See the sample photo on the right for a visual of paint fading.
Paint system warranties cover fading up to a certain Hunter Delta E (∆E) unit during a specific time frame. For example, if you have a 30-year warranty on color fading up to five (∆5) Hunter units on a metal roof and you think the paint has faded beyond ∆5 units before the warranty has expired, contact the manufacturer. They’ll come to the site and inspect the panels to determine if there was a failure in the paint system or if some other event has occurred to alter the color. From there, the manufacturer can investigate further and determine the correct course of action.
The warranty should spell out the ∆E units and if any specific colors within the warranty have variations. For instance, brighter colors generally have a less of a fade warranty and most metallic colors do not carry a color warranty at all because there is no way to measure them with a color spectrophotometer.
Most warranties will have differing ∆E units for metal roof panels and metal wall panels because the two are not subject to the same amount of sunlight (wall panels are typically covered at a lower ∆E number than roofing).
What is Chalking on Metal Roofing?
Chalking is the whitish residue that can become visible on a painted or coated metal surface over time. As a panel is exposed to sunlight and UV rays, the resin begins to break down and degrade. Once the resin starts to break down and continues to be exposed to the sun, oxygen, and other pollutants, it loses its adhesion to the surface and those degraded particles begin to turn white. These particles will eventually become visible to the naked eye on the metal’s surface. Often times, the difference can be subtle; however, if you swipe the panel with your finger, you can notice the chalky residue on your skin.
The degree of metal roof chalking is dependent on the paint system, especially the quality of the resin, used to cover the metal substrate. The rate of chalking based on resin type is usually in the following order (assuming the same environmental conditions apply to all):
- Plastisols (First to chalk)
- Fluoroethylene vinyl ether (FEVE)
- Polyester (Mid-range)
- Silicone-modified polyester (SMP)
- Polyvinylidene fluoride (PVDF) (Last to chalk)
Measuring Metal Panel Chalking
Chalking is measured using one or more of the methods defined in the ASTM D-4214 standard. This standard also defines parameters for the numbering system, ranging from Number 1 to Number 10 (with Number 1 being the worst and showing signs of extreme chalking). Warranties often cover chalking in excess of a specific number using a specific method to determine that number.
For example, if a manufacturer says that their warranty covers chalking in an excess of number 8 using Method A, also called the Cloth Tape Method, the testing process would follow these instructions:
- 7.1 Test Method A—Cloth Tape Method:
- 7.1.1 Material—Fabric, as agreed upon between the producer, user, or other interested parties, to rub against the surface being tested. Black (or white for dark coatings) wool felt, velvet, and velveteen have proven particularly effective.
- 7.1.2 Procedure—Wrap the fabric around the index fingertip, then make a 2 to 3 inch (50 to 75 mm) stroke with medium pressure on the coating under observation. Remove the fabric and compare the spot of chalk on it with Photographic Reference Standard No. (See photo on the right)
- NOTE—Medium pressure can be quantified by placing the finger on a balance or scale, and pressing downward until 3 to 5 pounds of pressure is obtained.
Testing Paint Systems on Metal Roofing & Wall Panels
It’s important to remember that manufacturers and paint suppliers test their paint systems in the harshest of conditions well before the products ever hit the market. These tests help manufacturers gauge how well their products perform so they can offer you and other consumers the correct warranty based on where your structure is located. This testing allows manufacturers and paint suppliers to test the panel’s resistance to:
(Note: Thoroughly read the warranty and make sure all of the resistance factors listed above are covered.)
Some of the common testing methods include:
- Natural exposure - Painted sample panels are arranged on long outdoor test racks to face south in tropical environments (typically Florida) so the panel gets the full force of the sun’s exposure. The paint samples are kept on the racks for a specific length of time to determine the paint system’s degradation cycle.
- Indoor accelerated testing – Product samples are put into machines that simulate actual weathering conditions, such as rain, wind, sunlight, heat, and humidity, to determine how well and how long different paint systems can endure the elements. While natural exposure is the most realistic measure of how well the product will perform, accelerated testing allows for the measuring of more materials over a shorter period of time.
Remember to ask your manufacturer about the testing methods their paint supplier uses before their metal panel systems hit the market and that they can substantiate these tests. It’ll give you a better understanding of how trustworthy the manufacturer and their products are if they are willing to have a conversation about the results of weather testing and if the products are in line with industry standards.
Wrapping It All Up
In the end, nothing will keep outdoor metal panels safe from chalking and fading forever. But that doesn’t mean there aren’t ways to stretch out the life of a metal roof or wall panel system. Being proactive instead of reactive truly will make a difference. Always remember:
- Ask the manufacturer about what paint system will work best for where your structure is located
- Your contractor might know the answer to this, but it’s best to go directly to the source of the materials
- Educate yourself on the paint system you end up choosing; it’ll help you determine if something is a legitimate issue or potential claim
- When deciding the system to go with, consider the useful life cycle of the paint system and importance of maintaining a particular finish for the duration of that life cycle
- Remember that these paint systems are put through vigorous weathering tests to ensure they are ready to perform to a high standard
- Ask for a maintenance and cleaning guide for the metal and paint type upon purchase
- Most importantly, follow the instructions in the guide
- If you think you have a claim regarding chalking or fading, don’t try to remedy the problem on your own; call the manufacturer as soon as possible
Here at Sheffield Metals, we ensure our metal coil and panel systems are top of the line by partnering with trusted paint companies, like Valspar and Sherwin-Williams, that make sure their systems exceed industry standards—especially when it comes to chalking and fading.
We want to answer your questions, so contact us today to speak with one of our knowledgeable experts.