Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Painting Anodized Aluminum
Q. Hi. I have a anodized aluminum part that I need painted. the part will be used for an outdoor sculpture in San Diego, and therefore exposed to high heat..rain..etc. I am not sure what paint/coating process would be the most appropriate for such a piece...also I have been getting both negative and positive responses to painting anodized aluminum. if anyone can help me I would greatly appreciate it.
---the part is 6" x 6" x 1/2", and only one of the 6" x 6" faces is getting painted ... are some processes better or worse for parts that need to be masked?
westford, Massachusetts
1999
A. Yes you can anodize aluminum to serve us an under coat for paint and it is used in Italy now as a replacement of chromate on aluminum But you should note the following:
- The aluminum material should be the type you can anodize
- After anodizing it should not be sealed
- A very good rinse is essential, preferably with demin water
- The anodized layer is preferable not to exceed 5 microns
My experience is only with polyester and epoxy powders electrostatically applied and cured in convection ovens. For other types of coating you should consult others. Good luck.
Khalil Sawalha- Amman Jordan
Multiple threads merged: please forgive chronology errors :-)
Q. I am an architect. I have a site where the contractor has ruined the finish on a metal clad wall (anodized aluminum). Can anodized aluminum be painted over in the field? How do you prep and what type of paint do you use? Finally, this is in the northeast, are there any temperature constraints involved?
Martha Lane- New York, NY USA
2000
A. Yes, anodized aluminum can be painted, I believe it must be processed first with zinc dust ⇦this on eBay or Amazon [affil links] on chromic acid anodized, water sealed aluminum parts. Can anyone suggest methods for improving the adhesion? In addition, can anyone suggest a method for improving subsequent paint adhesion on similar parts after they have been stripped (via plastic grit) of previous paint coatings?
Aryeh Asher- Ashkelon, Israel
A. The list is potentially endless.
Air quality used in spraying. It should be oil and water free. Check it by passing the air over a small mirror.
Purity of the rinse-water. Anything above 200 micro siemens for deionised water is potentially problematic.
Spray rinsing on exit followed by immersion rinse can reduce carry out and helps maintain rinse water quality.
You can also have problems with temperature and humidity whilst spraying. High temp and low humidity can cause the primer to flash off too quickly. Low temp and high humidity can also cause adhesion problems. Primer application may be too slow. Apply several wet coats in a box pattern.
Curing times. Make sure you hit the full cure on these primers. A little longer at the cure temp doesn't normally hurt.
A lot of these primers settle very quickly. It probably needs to be agitated and preferably in a recirculating system.
If it is a single component (cold stored/frozen) primer is it being allowed to reach room temp before being opened. If he already has all these correct then it is always well worth contacting the primer manufacturer. Their technical depts will quite often visit and spot something straight away.
- Great Britain
Multiple threads merged: please forgive chronology errors :-)
Q. I am looking for information regarding painting of anodized aluminum surfaces, specifically alloy 6063 T5.
In addition, I am also seeking information on powder coating such surfaces and the application of Kynar finishes to such surfaces.
Dan HilburnBalco, Inc. - Wichita, Kansas, USA
2001
A. I can't help with powder coating but the first step after anodising is normally to apply a corrosion inhibiting primer to an anodised finish. Any serious adhesive supplier (particularly aerospace adhesives) will be able to supply one. They are normally chromate based but the choices are numerous. 3M, Cytec, and Hexcel all produce excellent versions. HVLP spraying of water based is now much more common so no major difficulty equipment wise. Most of them used to be high solvent content and these are still available.
Ciaron Murphy- Great Britain
Large scale painting of anodized aluminum
Q. Some HVAC louvers were delivered to a construction site with and clear anodized aluminum finish due to an error in the approval process and we are stuck with them. I've read past letters and responses concerning the stripping of the anodizing which address small scale and shop oriented stripping and painting processes.
I have to change the color of approximately 100 two foot by six foot (.6 X 1.8 meters) louvers but need to do it in a cost effective manner (= not sending them somewhere), in a limited amount of space and with the limited resources of a typical building construction site.
It sounds like sand blasting, followed by priming and painting is my only option as I can't see how to dispose of large amounts of caustic materials from the site.
Is there and electrostatic method of painting that I might be able to set up on site and avoid the stripping?
- Rochester, New York, United States of America
2002
A. I'd say just paint them with a direct to metal paint ⇩. Although ideally anodized aluminum should not be sealed before painting, it is very corrosion resistant and I don't see the advantage is trying to strip off this corrosion resistance before painting.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Update: Thanks to further suggestions posted here, direct to metal paint doesn't sound ideal to me anymore. But I think a self-etching primer ⇦this on eBay or Amazon [affil links] should stick pretty well to anodized aluminum.
Q. To Whom It May Concern:
We start with a blank piece of aluminum and machine artwork into it, let's say an American flag. Now, every other stripe is machined below the surface, and the material around the stars has been removed.We then send the piece out to be anodized red.
After receiving the part back from the anodizer we paint blue over the anodized area around the stars. After the paint has cured we take a very light cut off the surface (about 0.010). The stripes that were recessed in the material remain red anodized, every other stripe is now bare aluminum, giving the look of the white stripes. Since the tops of the stars were also on the same plane as the white stripes they are also bare aluminum but the blue remains between them because it is below the top face of the part.
Now, the paint does not seem to stick to the anodize very well. We specifically asked the anodizer to use a water seal so we could paint on top of the anodized surfaces. We have tried several different paints but can't find one that sticks to the anodized surface and remains durable. Also, on some pieces that surface area that is bare aluminum after we take the light cut off is fairly large. We want to buff these areas to a 'mirror like' finish before sealing with a clear coat. During the buffing process the paint is often pulled from the surface of the anodize. We are looking for a durable paint that adheres well to the anodize.
The artwork is fairly small so masking would be difficult. Basically, we are trying to get multiple colors on an anodized part in a relatively efficient manner. We know this is a difficult task and are open to suggestions. Thanks.
Design Engineer, TPR Inc. - Mentor, Ohio, USA
2006
A. Anodized aluminum requires an etch primer. The 2k version being the better choice for longer lifespan. Use an acrylic lacquer or 2k top coat system for finishing.
Regards,
Fons
- Melbourne, Victoria, AUSTRALIA
October 16, 2008
A. A self etching primer
⇦this on
eBay or
Amazon [affil links]
, or aluminum wash primer (containing acid) are the recommended primers that promote adhesion. Another option is duracoat, or cerakote. Both are 2 part solvent based paints. Duracoat
⇦this on
eBay
or
Amazon [affil links]
is cheaper, more user friendly, and plenty durable. Cerakote
⇦this on
eBay
or
Amazon [affil links]
is baked on after application, less user friendly, more expensive, but tougher overall.
DTM paints are not made for aluminum. The good ones are emulsified oil in a water base, and will adhere a little better than house paint after a 30 day cure. The cheaper DTM's are 100% acrylic ie: house paint. if it's art, it doesn't need to be durable, just have good uv protection and color retention. ceramic paints and ceramic clearcoats lead the pack in that department.
- West Sacramento, California
February 1, 2024
Multiple threads merged: please forgive chronology errors :-)
Painting Anodized surface
Q. Hello,
I have some parts 6061 T-6 that are sulfuric acid anodized and dyed black. I am being asked to paint them gloss black. I will prime them and Topcoat, but my question is - how do I prepare the surface? If I lightly sand the surface to accept the primer to a tape test condition will I not destroy the anodized surface?
Do I have any leeway?
Sincerely,
- Savannah Georgia USA
November 10, 2015
A. 600 grit water sanding will not hurt the Anodized coat. That is followed by automotive primer and Single stage Urethane gloss black.
Marvin Sevilla- Managua, Nicaragua
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