| Author |
Message |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 788
Registered: 05-2003
| | Posted on Wednesday, March 14, 2012 - 11:31 am: |    |
Typcially we specify Liquid Resin coating for exterior aluminum on our projects, with advancement in Powder coatings we are now being asked to spec Powder, esp on Green projects. What is the difference in the actual spec between Powder and Liquid, need help on updating our specs for fenestrations and detail work. |
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 856
Registered: 10-2002
| | Posted on Wednesday, March 14, 2012 - 11:45 am: | |
Jerry,
Are you talking about powdered fluoropolymer vs liquid fluoropolymer
or
powder coatings in general vs liquid fluoropolymer?
Powderized fluoropolymer is an extremely durable material and PPG recommends it for coastal environments and provides it with a 30 year warranty against chalking, fade, etc. Their liquid fluoropolymer (70% kynar resin or 100% Lumiflon resin based) is a 20 year warranty.
If you are talking about powder coatings in general vs liquid fluoropolymer, its typically only european powder coaters that will give you a warranty for fade and chalk resistance greater than 15 years. Here in the US they don't like to go over 10 but when really pressed with competitive requirements will sometimes go to 15.
And it all depends on what is being powdered. You can powderize almost anything, from latex and acrylics to enamels, polyesters and polyurethanes. When the powder coating industry speaks of better or increased performance, they are comparing it the liquid form of the same coating. But they typically don't phrase it that way, and its common to think they are speaking of greater performance than any liquids. But that is not true. And once you are on that train of thought, they typically don't bother to correct you.
William
William C. Pegues, FCSI, CCS, SCIP Affiliate
WDG Architecture, Washington, DC | Dallas, TX |
Jerome J. Lazar, RA, CCS, CSI, SCIP
Senior Member
Username: lazarcitec
Post Number: 789
Registered: 05-2003
| | Posted on Wednesday, March 14, 2012 - 12:32 pm: | |
William
Aluminum extrusions for windows and doors, are current Finish spec as follows:
Exterior Aluminum Surface Finish: Electrostatically applied thermosetting Kynar flouropolymer resin coating with inhibitive flash primer over chromate conversion coating. Meet or exceed AAMA 2605 standards. Submit color samples for approval, color to be selected by Architect.
1. Chemical Pretreatment (AA-C12C40R1X): Aluminum shall be cleaned with inhibited chemicals and the surface chemically converted to amorphus chromium phosphate to conform to ASTM D 1730, Type B, Method 5, prior to coating. Conversion coating weight must exceed 40 milligrams/square foot. No substitutions for amorphus chromium phosphate (conversion coat) will be permitted.
2 Fluoropolymer Three-Coat System: Manufacturer's standard three-coat, thermocured system consisting of specially formulated inhibitive primer (strontium chromate), fluoropolymer color coat, and a clear fuoropolymer top coat, with both the color and clear coats containing not less than 70 percent polyvinylidene fluoride resin by weight. Prepare, pretreat, and apply coating to exposed metal surfaces to comply with AAMA 2605 and with coating and resin manufacturers' written instructions. Provide coating which has been field tested under normal range of weathering conditions for a minium of 20 years without significant peel, blister, flake, chip, crack, or check in the finish, and without chalking in excess of 8 (ASTM D 4214) and without fading in excess of 5 NBS units.
3. Color to be tested and certified by the storefront glass system manufacturer to comply with AAMA 2605.
4. Coating system shall provide 1.60 mils dry film thickness consisting of 0.25 (+/- .05) mil primer, minimum 1.0 mil colorcoat, 0.60 (+/- .20) mil) clear top coat. |
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 857
Registered: 10-2002
| | Posted on Wednesday, March 14, 2012 - 01:19 pm: | |
Yes, that is the typical hylar/kynar resin liquid fluoropolymer coating spray applied for extrusions or other component items.
The best of the powder coatings as available in this country can't come close to its performance yet.
Metallic and mica based colors - this is still very difficult to achieve with the powder coatings. I don't think there are any US applicators that offer metallic or mica type colors. "Silver" yes, but others, no or very rare.
In addition there is the issue of touchup and future recoating, especially with high hand contact ares like handrails. You can get the exact color in and even match the metallic and mica colors now with an electrostatic spray. I have done whole metal panel buildings (built in the 1960s) that were recoated from top to bottom in the field with no problem. This is using a product like PPG's Coraflon which is their 100% Lumiflon resin fluoropoloymer system which is an air dry system. You can even get a 10 year warranty on their air dry system.
William
William C. Pegues, FCSI, CCS, SCIP Affiliate
WDG Architecture, Washington, DC | Dallas, TX |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 173
Registered: 12-2006
| | Posted on Wednesday, March 14, 2012 - 02:09 pm: | |
As far as I understand, the aluminum still requires the chromium phosphate pretreatment which, unfortunately, is probably the worst part of the system environmentally. As William noted, powder coating mica and metallic systems really isn't achieving the finish yet. Apparently the flecks can't 'stand up' and so don't provide the same look as when they are applied in liquid.
A look that is available in powder coating is similar to the 'Zolotone' multi-colored effect. Each little paintball that gets melted onto the surface is specifically color blended. Combining different colored paint balls in a powder coating mix will result in multiple colors; they don't blend on the surface. I haven't seen anyone put that fact to use yet; not sure I want to. Still, who knows what we'll be seeing as this technology increases in popularity.
Another neat new development in powder coating involves MDF. How they manage to put an electrical charge on a piece of MDF and then melt the coating onto the wood composite surfaces I have no idea but it's becoming very available. |
Dave Metzger
Senior Member
Username: davemetzger
Post Number: 418
Registered: 07-2001
| | Posted on Wednesday, March 14, 2012 - 02:38 pm: | |
I Googled "powder coating MDF" and found many hits.
According to one site, "MDF has a natural water content of typically 5–7 percent. The new system developed uses this as a means to make the board conductive. By quickly raising the surface temperature of the MDF to 200 deg.F for a total dwell time of up to 2 minutes in a catalytic IR Preheat Oven, the board becomes conductive and remains so for up to 5 minutes after leaving this oven. Board temperature at application is 120 deg.F to 150 deg.F which is well below the temperature at which the powder would fuse or melt to the MDF. Once the board is conductive, the powder is easily attracted to the MDF, ensuring a high degree of transfer efficiency. The attraction causes powder to wrap around the board perimeter in a similar fashion to metal. Once the powder is evenly deposited on the board surface and around the edges, the board enters into a catalytic oven for the 5 minute curing process."
The manufacturers I looked at all noted the durability of this coating on MDF. But there wasn't anything in the way of standardized testing, if such even exists. One manufacturer had a video of someone tapping a small piece of powder-coated MDf with a hammer--hardly a replicable test.
I remember back in the 1950's when chrome-plated plastic ballpoint pens were popular. They looked great until they developed a little blister, then it was easy to pick at the blister and peel off the metal plating. |
Anne Whitacre, FCSI CCS
Senior Member
Username: awhitacre
Post Number: 1252
Registered: 07-2002
| | Posted on Wednesday, March 14, 2012 - 04:16 pm: | |
I never use a fluoropolymer for handrails -- I just don't think they hold up very well. I would suggest you look at some of the water based urethanes and epoxies from Tnemec for field application. I use these products for exterior doors and handrails -- they can match anything (metallics included); they wear better than any powder coat under repeated hand contact, and they can be applied after installation, so there are no issues with welding damaging the coating. |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1367
Registered: 03-2002
| | Posted on Thursday, March 22, 2012 - 11:21 am: | |
Unless the Kynar applied in powder form gets better performance than that applied in liquid form, why should you care? The performance standard mentioned, AAMA 2605, does not distinguish method of application, just long-term performance of the completed coatintg. More likely, the original question concerns powder-coated polyester finishes, which can indeed have a very long life. However, I don't know of any standard for performance for these, which has been historically the situation. Does anyone know any different? |
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 858
Registered: 10-2002
| | Posted on Thursday, March 22, 2012 - 11:50 am: | |
Powderized 'kynar' (such as the powder form of Duranar from PPG gets their longest most durable warranty, 30 years. They specifically recommend it for high sun, high salt environments. So, powdered fluoropolmyer gets amazingly better performance than liquid applied.
Typically powder forms of any coating have an extended lifer over their liquid forms. However, even the powder forms of polyesters and polyurethanes won't warranty their product for more than 15 years. Some may but its rare, and its even pulling teeth for a warranty over 10 from them.
There is no standard of performance other than the AAMA coating series of standards, so, 2605 is it, and all it does is set the floor for wear and tear, exposure, weathering, etc. Pass them and you comply. Some pass marginally, some like the fluoropolymers exceed considerably.
Regarding handrails, I agree with Anne, and that is what I used to do all the time. Unfortunately, the handrail industry has moved aggressively into powder coatings. The powder systems themselves make touch up or recoating later very difficult, lots of surface prep and then you are doing just a liquid air dry polyurethane or polyester or sometimes just an acrylic.
Now however, I have no hesitation in specifying them with a fluoropolymer, especially if its a metallic or mica coating. PPG has their air dry system Coraflon which can be field applied, including metallics and micas. It even comes with a 10 year warranty. Coraflon is based on their next generation 100% resin, Lumiflon, which is compatible with the kynar 50% resin systems for recoating and touchups. I have been doing that for years. I also use it for the various small feature items that need to get a coating matching primary items like curtain wall or metal panels but which are going to be fabricated by someone else and not make it to the coating line. In that case, it is shop coated rather than field coated. Excellent success with this for many years now (started doing this in 2002).
Also, we had 3 existing high rise office buildings that we did back in the 60s for an owner who in 2002 came to us for solutions to their coatings. Back then, it was a porcelain steel metal panel system with ribbon windows, everything was a real dark brown. We brought in PPG for the special surface prep that would be required since the panels curtain wall components had been field repainted in the mid 1980s with who knows what. Then all 3 buildings were recoated in the field.
So I have no hesitation using fluoropolymers on handrails or other piece items where color matching is required.
William C. Pegues, FCSI, CCS, SCIP Affiliate
WDG Architecture, Washington, DC | Dallas, TX |
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