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  #1  
Old 03-16-2009, 06:43 PM
ews ews is offline
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Powder Coating for exterior use

Hi All.

I need some real world advice on Powder Coating. I make small bird sculptures out of recyled garden tools, and I have previously finished them with a 3 coat paint finish, using a brand of paint here in the UK called 'Hammerite'. This is for exterior use, I would like to use a Hammered or Metallic Finish Powder coating, it seems a Polyester type powder is refered to. Any one have experience of this type of coating and to its life span before it breaks down, UV degradation or weathering.

Any advice out there ?????
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  #2  
Old 03-16-2009, 07:50 PM
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cheesepaws cheesepaws is offline
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Re: Powder Coating for exterior use

I want in on this too.

I've been invited to work with some students on designing and fabricating some artsy bike racks which will (most likely) get powder coated. Do you have to drill holes any capped metal tubing to account for the heat expansion concerns (like you do with hot-dip galvanization)? I have heard that there are fillers that can be used for powder coating - are they effective (do they chip easily)? How prepped does the surface need to be (assuming mild steel)? Need it be sand blasted or can it still have some scale on it?

Thanks in advance.
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  #3  
Old 03-16-2009, 08:06 PM
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evaldart evaldart is offline
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Re: Powder Coating for exterior use

Hammerite is a GREAT product (if it must be painted). Powder-coating will numb and pacify anything it touches.
Cheese, NOTHING can stand up to chains and locks...its a waste of time to expect any coating to perform more than a month under bike-rack conditions. You've just got to do it in stainless (or its weak sister, aluminum).
Leave the powder coating for the gym equipment and the Paley sculptures.
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  #4  
Old 03-17-2009, 11:46 AM
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Ries Ries is offline
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Re: Powder Coating for exterior use

Hmm- I find Hammerite to be goopy, drippy, and inconsistent in its hammer finish- some spots are nice and flaky looking, other times it gets all smooth.

It always drips when I use it, and makes things look much more "numb" than powder coating.

Most commercial bike racks are powder coated.

That said, I am not a big fan of powdercoating for exterior use, and NEVER do it for paying jobs, where there is a chance the customer will call and complain to me if it fails.

Powder coating is kinda unpredictable. IF it is sandblasted first, then powdercoated by a professional shop, with a good 5 step or better precoat line, and who know what they are doing, MAYBE it will last outside. And maybe it wont. Once powder starts to go, it peels up erratically like a bad sunburn, but enough of it sticks that its impossible to repaint without time consuming and expensive sanding.
Pro powdercoaters use a burnout oven of over 1000 degrees farenheit and THEN sandblast, if they have to remove old powdercoating. Its tenacious stuff, especially if you want it off.

I used to do a lot of furniture and production stuff, with hammered and wrinkled finishes, and I think they are some of the best powders- textured finishes show scratches and damage much less, and they often stick better than smooth glossy ones.

But there are no guarantees about longevity of powder outdoors, and its such a bear to recoat- at a minimum, you would need to de-install and sandblast- that I just plain dont use it.

For small sculptures though, where the dollar amounts arent too high, and there arent big installation/de-installation costs, its worth trying.

I have had powdercoats fail outdoors in less than 2 years- and then, I have a railing I made for my back porch, that was sandblasted and done properly, in black wrinkle, that is still doing great after almost 15 years. Go figure.

The best source of strange textured finishes is Prismatic Powders- they make some of the highest quality, longest lasting, and least "painty" looking powder coats.
Probably not available in the UK, though.
http://www.nicindustries.com/prismatic_powders.php
Their stuff is expensive, and worth it.

But I re-emphasize- Quality of the shop doing the powdercoating is the most important thing, and there are way too many fly by night guys out there right now who say "how hard could it be?".
A good powdercoater will have between $500,000 and $1,000,000 invested in equipment, with automated 5 step pretreat lines, good ovens and guns, sandblasting and burnout on premises, forklifts, packing, and inventory of powder.
Plus, experience is paramount. Powder does weird stuff, different metals react differently, different thicknesses of the same metal act differently, and only experience will know that.
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  #5  
Old 03-17-2009, 02:03 PM
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evaldart evaldart is offline
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Re: Powder Coating for exterior use

Agreed Ries, but dont you just get mesmerized by that ground glass and ground aluminum floaty thing the Hammerite does, I can live with the goop...paint does that. I think its fun to slop-on. And they've got some really wierd colors too.
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  #6  
Old 03-17-2009, 05:47 PM
ews ews is offline
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Re: Powder Coating for exterior use

Many thanks to evaldart and Ries for your comments.

My first experience of Powder Coating was a disaster, two birds coated with the same antique copper finish, the one kept indoors looks as good as new after 3 years, the one outside peeled and degraded with in 1 year, the coater cut corners, it did not seem to have been sand blasted or primed, probably not even degreased, just a top coat !!!!!.

I have recently had two more powder coated at a different outfit, this one has many accreditations, and works to quality standards for many other industries, as well as having a personal touch, quite happy to spend time one small one offs. In fact the guys found my items interesting, were a change from the normal production work and were quite proud of of the end result. The proccess my items followed was, sand blasting, degreasing, primer and top coat, with a smooth paint like finish.

Edward.
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  #7  
Old 03-17-2009, 09:32 PM
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cheesepaws cheesepaws is offline
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Re: Powder Coating for exterior use

Thanks to you guys as well.

Luckily, someone else is flipping the bill. Luckily, I think they are actually more interested in using these bike racks as a springboard for future public sculptures on campus (of which we only have one - a bronze of the founder). I am approaching it as if they are temporary - so the finish need only last a short while. Once they get too ratty - a future class can replace them with newly designed racks.

Not really set up for stainless or aluminum work quite yet (and the students are far from ready) - still, I like the challenge of working with what we have. I'll post pictures as things develop.

Oh - no reply on the need to vent capped tubed stock - any opinions?
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  #8  
Old 03-18-2009, 12:31 PM
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Ries Ries is offline
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Re: Powder Coating for exterior use

No, you dont need to worry about capping tube.

This is only a problem with hot dip galvanizing, where any moisture in the sealed tubes turns to steam, and then sometimes explodes. Galvanizers frown on pieces exploding while in their tanks of 800 degree molten zinc, for obvious reasons.

But powder coating temps are much lower, usually no more than 500 degrees, and usually less. So interior sealed spaces are not a problem with powdercoating.
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  #9  
Old 03-18-2009, 08:51 PM
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cheesepaws cheesepaws is offline
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Re: Powder Coating for exterior use

Thanks Ries.

I met with the students today to review their first attempt at designs and was very impressed by their ideas and excitement.
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  #10  
Old 03-25-2009, 05:02 AM
Rick Clise Rick Clise is offline
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Re: Powder Coating for exterior use

'Early' on I had some outdoor metal sculptures powdercoated, using black, blue and green colours. Mainly over a gritblasted base. A couple pieces were over hot dip galvanising, and THAT really tested the powder coater. The good ones dealt with it and the resulting sculpture is still going strong with no deterioration of the black powdercoat 3 years later despite being in the harsh Adelaide weather.

The blue and green changed colour over a period of a couple years - didn't flake off but began to lose the richness of the colour. Done by the same powdercoater as the black over HDG.

The not as good coaters had BIG problems applying over HDG and what resulted were lots of craters from gas coming-out of the HDG when the piece was cooked in the coater's oven.

I've stayed away from using any bright coloured powders for outdoor pieces because of concerns about UV stability. Two pack industrial coatings have served me well here.

An outdoor metal table in 'antique silver' (textured) powdercoating that we own needed blasting back to bare steel and recoating after 11 years in the sun.

Earlier comments about how difficult powdercoating is to remove are right - my gritblaster frowns whenever I bring a previously powdercoated piece to him.

But it has its place. I use it for many indoor utilitarian (vs sculptural) items.
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