 What organic coatings does SAF recommend for exterior use on architectural aluminum?- What is PVDF?
- Why do you call it "coating"? Why not painting?
- What is a conversion coating?
- Can SAF paint steel?
- How long does it take?
- What is powder coating?
- Is alloy important if I plan to have my aluminum painted?
- What is an alkaline etch?
- How uniform can I expect the color of an organic coating to be?
- How should I specify a PVDF spray coating for aluminum?
- Do AAMA 2603, 2604 and 2605 specifications apply to flat sheet?
- How do I decide between painting and anodizing?
- What about rack marks?
- How do I clean painted aluminum?
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What organic coatings does SAF recommend for exterior use on architectural aluminum?
In the last five years, answering this question has become more complicated! Answering was once as simple as saying: "For exterior architectural use, Southern Aluminum Finishing recommends 70% PVDF finishes." Today, the are many alternate coatings being used and specified. Coatings like Polyester TGIC powder coatings, 50% PVDF and even non-PVDF Fluorocarbon coatings have their applications. Contact SAF for more information. You may be able to save money using one of these alternate coatings if the application is right.
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What is PVDF?
It is a resin used in architectural coatings that has exceptional weathering characteristics. PVDF stands for polyvinylidene fluoride. It is also known as "Kynar", or more properly, ?Kynar 500. ?Kynar 500 is a registered trade mark of Arkema Inc. North America, Inc. To quote Arkema: "Kynar? polyvinylidene fluoride (PVDF) resin is one of the most stable and pure of all commercial resins. It resists strong acids, solvents, and reducing agents and is used in several industries, including electrical and electronic manufacturing, chemical processing, pulp and paper, and transportation." The word Kynar is being used in everyday conversation the way the trade name "Kleenex" is used with tissues. However, as long as Arkema continues to protect its right to the trade name "Kynar 500," the generic way to describe it is "polyvinylidene fluoride" or "PVDF." This is not exactly the same thing as "Fluorocarbon resin." PVDF is one of several Fluorocarbon resins. Another trade name used for PVDF is ?Hylar 5000. Hylar 5000 is a registered trade mark of Solvay Solexis. For more information about PVDF coatings, please refer to kynar.html
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Why do you call it "coating"? Why not painting?
The two most common kinds of paint that we encounter in our every day lives are house paint and automotive paint. Neither has a life expectancy of more than ten years and both require on-going maintenance. Most of SAF's business is in applying coatings that have a 20-year life expectancy. This puts our coatings in a totally different category of product. We measure our coatings using criteria that are completely different from house paint. Comparing our coatings to "paint" is like comparing apples and oranges
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What is a conversion coating?
A conversion coating is a chemical treatment applied to aluminum. It is also known as a "chrome phosphate" coating. It is usually done prior to painting, and is accomplished by immersing the aluminum in a chrome phosphate solution. The finish provides some corrosion resistance, and more importantly, good adhesion. It is typically used as the base for an organic coating. There are actually many kinds of conversion coatings, some based on chrome and some used on other metals. Sometimes it used as a final finish, but this requires the use of a very strong bath. Most paint applicators do not maintain a strong chrome bath because it is not required for paint pretreatment.
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Can SAF paint steel?
No. Steel requires a different pretreatment than aluminum. The pretreatment for steel is known as "phosphatizing" and SAF does not do this process.
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How long does it take?
It only takes a few hours to process and pack a part. Most coaters need anywhere from a few days to a few weeks to plan, process and invoice for projects. Lead times of longer than four weeks for painting are rare.
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What is powder coating?
Liquid paint is composed of pigment, resin, and solvent. Powder coatings are simply pigment encapsulated in a powdered resin and is thus simply thought of as "paint without the solvent."
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Is alloy important if I plan to have my aluminum painted?
Yes, according the Aluminum Extruder's Council, alloys 6061, 6105 and 6063 are best suited for painted applications. Since painting is obviously quite different from anodizing, keep your metal supplier informed of finishing requirements. This will result in better advice in all areas of your order.
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What is an alkaline etch?
Etching aluminum in sodium hydroxide is by far the most common pretreatment for aluminum that is to be anodized. Alkaline etches are also used to strip off anodic coatings prior to painting. However, under no circumstances should an etch-only finish be used in a finish product because there is no way to prevent the rapid onset of corrosion. An etch-only finish normally is regarded as an unsightly mess by our customers. It must be anodized or painted immediately after etching to protect the metal.
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How uniform can I expect the color of an organic coating to be?
If you have all the metal for a given job painted at the same time, in a single set-up, the coating should be uniform. However, most paint manufacturers expect their paints to vary a little from batch to batch, usually less than 2 delta E as measured by AATCC Test Method 173-1998. This can result in a barely noticeable difference in color between batches of paint. However, the differences can be larger with a translucent or metallic coatings. For more information about metallic coatings, please see metallic.html
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How should I specify a PVDF spray coating for aluminum?
SAF recommends the use of AAMA specifications. AAMA stands for the American Architectural Manufacturer's Association. There are three AAMA specifications that address spray coating architectural aluminum:
| AAMA specification |
AAMA 2603 |
AAMA 2604 |
AAMA 2605 |
| Compared to old specification: |
Same as AAMA 603 |
Similar to AAMA 605 |
New specification |
| Salt Spray resistance |
1500 hours |
3000 hours |
4000 hours |
| Chalk Resistance |
Slight chalk at one year |
Chalk = 8 at 5 yrs |
Chalk = 8 at 10 yrs |
| Color retention |
Slight fade at one year |
Fade = 5 delta E at 5 yrs |
Fade = 5 delta E at 10 yrs |
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Do AAMA 2603, 2604 and 2605 specifications apply to flat sheet?
Only if the sheet is spray coated. Most flat sheet is coil coated. There is a different AAMA specification for coil coated sheet. Please contact AAMA for more information.
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How do I decide between painting and anodizing?
Please read our article on this web site on this topic. Click here.
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What about rack marks?
Mechanical contact must be made to each part that is painted. The heavier a part is, the bigger the mechanical contact required.
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How do I clean painted aluminum?
Care should be taken when cleaning painted aluminum. Regardless of the technique used, be certain to test it in an inconspicuous area first. Because there are many different kinds of paint, you should first contact the original manufacture of the paint for a recommended cleaning technique. Do not use an abrasive cleaning technique! Do not use harsh acidic or alkaline cleaners because they may destroy the finish. Use solvents with care as they may stain the finish. The best specification available for cleaning architectural coatings applied by SAF is AAMA 609-79. A copy of this specification can be obtained from the American Architectural Manufacturer's Association. SAF also works with a field renovation service called SAF Renovations. SAF Renovations can help with restoring a painted architectural aluminum finish.
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