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Powder coating

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John Rutzen02/03/2020 15:11:53
247 forum posts
12 photos

I was really inspired by that video someone posted the other day about paint preparetion because I've never had good results with paint adhering on my model locos.. Powder coating seems the way to go but the only spray guns i can find on Amazon are the chinese ones .. Has anyone any experience of these? There are no reviews on them to speak of.There is a UK supplier of the american eastwood ones but quite pricey. The chinese ones on amazon are on quick delivery and apparently come from swithzerland so shouldn't be shipping extra charges or a long delivery time,

Andrew Tinsley02/03/2020 16:39:50
1169 forum posts

I have had quite a few items over the years, which have been powder coated. Each and every one has peeled over time. It seems that once there is a small hole in the coating, the underlying steel produces a thin layer of rust which spreads like the plague. The powder coating loses adhesion and flakes off.

Maybe I have just been unlucky, but I will stick to traditional painting in future. Even professionally coated bike frames have gone the same way.

Andrew.

Peter Simpson 102/03/2020 17:50:18
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169 forum posts
8 photos

I have a Land Rover Defender, it's coming up to 6 years old and looking to buy yet another side of powder coated side steps due to corrosion. Powder coating is fine for a TV stands etc, but hopeless where there is a chance of corrosion.

Dave Shield 102/03/2020 18:15:34
13 forum posts
1 photos

It was rubbish on my boat self steering gear as well.

michael darby02/03/2020 19:36:21
48 forum posts

Powder coating is a con. it is simply paint which is hardened in an oven. the paint drys before the base material is even warm and very hard. Once the item is in sevice,the material expands and contracts and the "Hard " paint cracks,allowing moisture under the top coat (no undercoat used). in all my time in contract engineering, I have never seen 1 successful application

Samsaranda02/03/2020 20:07:12
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952 forum posts
5 photos

I wouldn’t use powder coating, my experience is that it goes brittle and then flakes off, a waste of money. When I was working in industry we had pump assemblies painted to resist very harsh environments and the paints were phenomenal, as far as I can remember they were two part epoxies and applied in thick layers. I would source an epoxy finish for durability.
Dave W

Samsaranda02/03/2020 20:07:13
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952 forum posts
5 photos

I wouldn’t use powder coating, my experience is that it goes brittle and then flakes off, a waste of money. When I was working in industry we had pump assemblies painted to resist very harsh environments and the paints were phenomenal, as far as I can remember they were two part epoxies and applied in thick layers. I would source an epoxy finish for durability.
Dave W

Samsaranda02/03/2020 20:07:57
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952 forum posts
5 photos

Sorry double post - finger trouble.
Dave W

Chris V02/03/2020 20:32:29
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226 forum posts
31 photos

We had two radiators at different times powder coated and both are flaking paint off, never again!

Chris.

John Rutzen02/03/2020 20:55:08
247 forum posts
12 photos

hey thanks, if I think about it that's my experience of powder coating as well. I seem to remember garden furniture particularly. Looks like i saved a lot of money by asking the question. That aside the video about preparation for painting made some good points. The water droplet test particularly. I'll try scrubbing the metal with Ajax powder on my next try.

Russ B02/03/2020 21:15:50
575 forum posts
21 photos

I'm no expert but I know powder coating isn't a term used to describe one process, there are many different types of powder coat and like any paint job, the right powder, and the right surface prep, and proper curing are key to a proper job.

It's not paint, its ground plastic thats melted into a shell or a chemical mixture that cures into a shell - thus it can hold moisture against the surface, even spread it.

Epoxy types of powder coat aren't UV stable, like most plastics, excellent chemical resistance, but the sun kills it in a relatively short space of time.

I'd say the cons outweigh the pro's but perhaps the right power/prep/curing would improve its reputation??

Douglas Johnston02/03/2020 21:16:34
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699 forum posts
34 photos
Posted by Chris V on 02/03/2020 20:32:29:

We had two radiators at different times powder coated and both are flaking paint off, never again!

Chris.

I see I am not the only one to suffer this. Half an hour ago I was painting a section of a bathroom towel rail radiator that had been powder coated. Just as described above a small crack in the coating has resulted in the coating starting to peel off over an area of a few square inches. I am hoping that some radiator paint will halt the peeling.

Doug

Joseph Noci 103/03/2020 07:29:17
738 forum posts
940 photos

I must say that my experience seems to be contrary to all the above posts!

I powder coat everything that does not have to withstand heat and have not had any bad results, even in the long term. Even my machine covers, splash guards, etc are done so.

The key to success lies in the surface preparation, as with ALL painting methods, although powder coating is not a paint. Paint 'adheres' to the base material in two ways - mechanically, and chemically. If the surface is very smooth, like glass, the only possible reliable bond is a chemical one. Acid etch primers, for example, cause a chemical conversion at the contact layer, promoting the chemical bond - its more complex than that, but as this is about powder coating, I'll stop there..

Powder coating is a 'plastic' powder, flowed at its melting point, cured at around 70% of its melting point, and can only bond mechanically to the substrate.

This has to be clean, devoid of all oils, hydrocarbons, etc, fingerprints, etc. That is only one part - a truly clean, smooth, surface, does not provide a good bond to powder coats. The best way is to sand blast the surface, clean all dust with clean, DRY compressed air, and coat right away. I have made mild steel sheet metal covers, basically weather or environment 'wind and sun shields' for a solar powered electronic box that sits on a pole. These things are distributed along our north-west coast line, collecting data from Hyena and Lion collars, and are located between 50meters and 1km of the Atlantic ocean. Some have been there for 3 years now, with NO signs of coating delamination at all. It's all about surface prep.

Russ said it:

there are many different types of powder coat and like any paint job, the right powder, and the right surface prep, and proper curing are key to a proper job.

If you scratch the coating, through to the metal, post coating, then you invite trouble, but no more than if it were ordinary paint.

 

Joe

Edited By Joseph Noci 1 on 03/03/2020 07:29:33

David Jupp03/03/2020 07:41:57
737 forum posts
17 photos

Powder coat finishes are almost always porous to some degree (as are paints). In industrial applications, steel items are often galvanised prior to powder coating if they will be used in an aggressive environment, precisely because the powder coat won't stop moisture reaching the substrate.

David George 103/03/2020 08:06:23
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1301 forum posts
445 photos

I have used powder coating for specisl project's like machinery in the food industry ie jelly baby machines nougat bar machines. The frames had to be regularly washed and cleaned and so were powder coated and if done properly very little corrosion occurred. I had my garden gates done by the same company and after over 25 years shows little or no problems except for having to jet was them to get green growth off annually. You just have to check that the correct process is done ie grit blast prime and coat.

David

thaiguzzi03/03/2020 09:07:11
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698 forum posts
131 photos

Yep, sounds like the people with lousy experience have been using companies with poor preparation and quality control.

There is a reason why EVERY motorcycle manufacturer in the world have their frames and steel chassis components powdercoated.

Done correctly, with the right preparation, PC is the most economical, hard wearing, corrosion resistant paint surface available today.

My PC put on my 89 Guzzi in 2000 (20 years ago) is still holding up well. Perfect on steel surfaces, little chipping on the corner of an aluminium fork leg.

vintage engineer03/03/2020 09:27:35
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254 forum posts
1 photos

Powder coating is a plastic coating despite what everyone tell you. It is a cheap and quick process that gives an excellent finish for manufacturers and does not last and will fail as soon as you break the surface!

Mike Crossfield03/03/2020 09:51:25
229 forum posts
29 photos

A very interesting thread which is very timely for me. The alloy wheels on my wife's car willl need renovating soon, and I have been advised that powder coating will be much tougher than paint in this challenging application. A number of local wheel refurbishment specialists companies offer it, and it is more expensive than paint.

Is it all a con then?

Circlip03/03/2020 10:02:27
1167 forum posts

Useful when you don't want to watch paint drying. Surface prep essential.

Regards Ian.

Alistair Robertson 103/03/2020 10:10:17
96 forum posts
6 photos

A company that I worked for about 20 years ago manufactured aluminium cylinder heads etc. for a very well known engine maker. After they were made and tested they were finished with powder coating but it was not a simple process with at least four processes (or maybe more as I wasn't really involved) where they were blasted, dipped, painted, heat-treated and then the whole process was gone through time and again.

They were powder coated as a final process and I remember one of the managers saying that the painting/coating process was more expensive than the machining!

I was never in a position to afford one of these engines but a couple of years ago I came across one of them in the storage area of a motorsport company and when we blew of the accumulated dust the powder coating was as good as the day it left our factory.

So it seems it is not a case of simply applying some powder coating and hoping for the best. Proper preparation is absolutely critical.

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