Powdercoating question

[JTBoh]

Not a product we deal too much in, so figured I'd cross check it.

We're looking to install alum. letters and shapes flush to a concrete wall.
Was quoted for both sides of the aluminum, asked if 1 sided was an option for lower cost.

Cost is lowered, but PC guy says:
"Just so you know , if both sides are not completely coated it will give corrosion a place to start on the raw aluminum and it will creep under the powder coat and cause the finish to fail ."

Is it reliable enough to just coat one side, or will alum. corrosion really effect it? How long? Would it peel in flakes or just degrade over time?

 

[unclebun]

I don't think that is a problem commonly encountered. Automotive wheel manufacturers us powder coating as a finish, and they mask off parts of the wheel so that the finish can be variable, plus they don't powder coat the edge of the rim, as it would get ruined in mounting the tires. If corrosion of the edges were a problem, I don't think they'd use the process. Likewise, when we powder coat a motocross bike frame, mounting points and bolt holes are not coated (for reasons of fit) and we don't see corrosion failures at those points.

I would think if corrosion from the uncoated aluminum were a problem, we'd see it with painting only one side of aluminum as well. But in reality aluminum surface corrosion actually is self limiting. Once a surface layer forms, it prevents further reaction of the aluminum.

 

[Notarealsignguy]

The edges will be the problem but I dont really understand how you could reliable powdercoat 1 side. Its electrostatic so it wraps around the piece. The thinner film from not spraying both sides would be a concern to me but I don’t know 100% for sure.

 

[James Burke]

"Just so you know , if both sides are not completely coated it will give corrosion a place to start on the raw aluminum and it will creep under the powder coat and cause the finish to fail ." Is it reliable enough to just coat one side, or will alum. corrosion really effect it? How long? Would it peel in flakes or just degrade over time?

The only thing different with your application compared to the ones mentioned above is that the back side of your letters will be subjected to moisture that can not effectively dry out in a timely manner. As concrete retains moisture, the bare aluminum will not have the opportunity to form an oxide layer like it would if it were subjected to the air.

I guess you need to compare the cost of powder coating both sides versus prying out the letters to re-coat them.


JB

 

[Notarealsignguy]

I don't think that is a problem commonly encountered. Automotive wheel manufacturers us powder coating as a finish, and they mask off parts of the wheel so that the finish can be variable, plus they don't powder coat the edge of the rim, as it would get ruined in mounting the tires. If corrosion of the edges were a problem, I don't think they'd use the process. Likewise, when we powder coat a motocross bike frame, mounting points and bolt holes are not coated (for reasons of fit) and we don't see corrosion failures at those points.

I would think if corrosion from the uncoated aluminum were a problem, we'd see it with painting only one side of aluminum as well. But in reality aluminum surface corrosion actually is self limiting. Once a surface layer forms, it prevents further reaction of the aluminum.

Wheels are usually cleared including the lip. You dont put a tire machine in contact with the rim, just the bar to lift it.
Aluminum will continue oxidizing and will pop the powder coat, I see it everyday. It will rot right through. The backside wouldnt matter, itd take years to go through but the edges will creep.

 

[Ian Stewart-Koster]

why not 2-pack urethane paint, instead of powdercoat?

 

[MikePro]

overthinking it, i believe.
but if you're really worried then roll-on some killz latex to the backside of your letters prior to install day.