Powder coating quality of finish

[Sam SpoonsParticipant @samspoons83065]

I have just had a couple of bicycle frames powder coated with two different powder coating companies, the first is a 35 year old Raleigh Caprice and was done with a company described as 'cheap and cheerful'. It was in a very poor state and had some significant rust pitting, not structurally problematic but I expected it to compromise the final finish which it has. Despite that I'm very happy with the result given the original state of the bike and my wife is very happy with her 65th birthday present of her 30th birthday present bike restored to rather better than new.

The second is a 1980's magnesium mountain bike race frame, the original powder coater did not want to take it on as he didn't have the means to remove the original finish other than sand blasting which he felt was likely to be too harsh so I took it to another local company who were quite blazé about it, they have a good rep for doing alloy wheels and parts for high performance and race cars so I trusted that they knew what they were doing. I have just picked up the frame and am rather disappointed with the result which is thick and slightly orange-peel. The original finish was flaky but the anodised magnesium under it was smooth with little or no corrosion so I'm now wondering if they got too heavy handed with the blasting and left an excessively rough finish before coating it.

So a couple of questions, I know powder coating often has a slightly orange peel finish but is that inevitable? What media would you use to blast a soft material like Magnesium (I'm thinking soda?)?

FWIW I weighed the frame before taking it in, 1365g, and after 1500g so they have applied significantly more material than the original powder coating I had done about 20 years ago.

Edited By Sam Spoons on 10/07/2021 14:55:01

[Sam SpoonsParticipant @samspoons83065]

[bernard towersParticipant @bernardtowers37738]

Apparently it’s the time taken to heat (slowly) that has a big bearing on finish, a company round my way I use gets a finish like glass!

[Adrian 2Participant @adrian2]

My Norton commando frame had been heavily powder coated ,the finish was mostly ok. One down tube however was very poor, forget orange peel , think more like golf ball.

Powder coat can be over sprayed with cellulose which is what I did. Once flatted it provides a good base to overspray.

[Roger BestParticipant @rogerbest89007]

Sounds like they goofed.

I have a powder coated Mamod that looks like it was sprayed. It should have been good.

Edited By Roger Best on 10/07/2021 16:51:24

[noel shelleyParticipant @noelshelley55608]

Wouldn't give powder coating house space, far to much room for poor quality work that may only show up later ! Not easy to remove if it goes wrong ! Noel

[egaParticipant @ega]

Sam Spoons:

May we know the make of your magnesium frame, please?

I'm curious because I understand few makers have opted for this material.

[Sam SpoonsParticipant @samspoons83065]

I believe it's a Saracen Kili Flyer team XC race frame, I bought it off a dealer a long time ago, bare frame, anodised, said to be unused stock from when the company folded. It's not super light at 1365 g but it was cheap, is a bit unusual and still lighter than most, and it does ride well. It's been my spare bike for quite a few years, rigged as a single speed but, after the success with my wife bike rebuild, I decided I fancied something between the Orange G3 XC MTB and the road bike suited to the relatively flat South Manchester trails I ride with my buddy so it'll have 1 x 9 gears with a 32 or 36 chainring and 11-34 cassette and either gravel tyres or slicks depending on the weather. It's light for a MTB at just over 10kg (the Orange is nearer to 14kg).

Edited By Sam Spoons on 10/07/2021 20:16:01

[Sam SpoonsParticipant @samspoons83065]

Posted by noel shelley on 10/07/2021 17:41:11:

Wouldn't give powder coating house space, far to much room for poor quality work that may only show up later ! Not easy to remove if it goes wrong ! Noel

Yes understood but these guys have a good rep for coating bike frames so I had good reason to expect better, it was the blasting I was worried about which is what made me ask the second question about blasting media for soft metals.

 

I'm not sure whether to bother pursuing the matter, it's an old frame that has little value beyond sentiment and it was not an expensive job, £40 (though the other guys did frame, forks, mudguards, chain guard and handlebars for the same cost and, given what they had to work with, their result is no way inferior). It's not so much the not quite perfect finish that bugs me but the nagging feeling that they let the apprentice blast the bejesus out of it and then had to ladle on the coating to hide the cock up…. No way of knowing for sure I guess but there are a couple of divots in the finish where they hung it using a hole in the frame that won't be filled with anything so remains visible to remind me, I might just point those out and ask for a remedy…

 

Edited By Sam Spoons on 10/07/2021 20:30:08

[Mark RandParticipant @markrand96270]

Posted by Sam Spoons on 10/07/2021 20:14:27:

It's light for a MTB at just over 10kg (the Orange is nearer to 14kg).

Same weight as my Reynolds 531 Dawes bike in 1974, although that was a road bike and five speed.

[Sam SpoonsParticipant @samspoons83065]

Yes, road bikes are a bit lighter, my modern, relatively budget, road bike is about 10kg.

[John Billard 1Participant @johnbillard1]

I agree that powder coating can be very successful in certain applications but the result can vary.

I learned my lesson years ago when I had a set of wire wheels ex-Morgan powder coated. These can flex where the spoke enters the rim or hub thus fracturing the coating and causing corrosion to creep under it. This was never really resolved and the best cure was a new set of (painted) wheels.

Best wishes

John B

[Mark RandParticipant @markrand96270]

Re the corrosion:- Single coat powder coating is almost the worst process to use for long term corrosion protection if there is any chance of damage to the finish. Once there is a puncture in the coating that water can enter, rust will spread out from that point and lift the coating. As in, the Meriden Triumph spine tube motorcycle frames, which were powder coated very heavily and then had the frame number stamped on them.

Powder coating companies should offer to use a zinc primer layer for anything that is going to be outdoors or subject to damage. If they don't offer it up front, ask for it. My local coaters have been very good in that way.

[WindyParticipant @windy30762]

I have various disability outdoor hand rails on the house steps that are powder coated.

Two main rails are lasting well considering the years outside.

But two other smaller ones water has got under the coating and coating falling off with the corrosion.

They were both installed at the same time.

[Alan Johnson 7Participant @alanjohnson7]

My son-in-law has a patio fabrication business. All products are powder coated. I help him out as required – like today. I am the "trades assistant!" All that education, skill and knowledge gained through life is not required to be a "trades assistant!"

All powder coating powder is not created equal. Some are better than others, and the price varies dramatically.

Also, metal preparation is critical, and as he only deals with new steel and aluminium. I cannot comment about exotic metals, but I know from only working with new steel and aluminium that cleanliness is very important.

Outdoor products – like a steel verandah or staircase hand rail he has galvanised – after fabrication, and before powder coating. There is a "wait" of at least a week between the "hand rail" returning from the galvaniser before it is powder coated. It is also cleaned before coating.

Oven temperature is very important. Not hot enough is a disaster, as is too hot. Manufacturers of "powder" specify a minimum temperature and baking time. Equally, a maximum temperature and time.

The point of my post is that to make a living, the powder coater you choose will have to be attuned to the material that "he" is working with, so I can see that when an "exotic" job comes along – which he has limited experience with that it can all go bad.

Not much help really, but it does give some view on a "practical coal face" experience.

[Sam SpoonsParticipant @samspoons83065]

Thanks everybody, I'm inclined to just accept that it's not a perfect job as I'm away on hols next weekend for 6 weeks, but perhaps I'll run it past the guy in the local bike shop the recommended them and see what he thinks. I can't see them being able to do anything about it if they have cocked it up, I guess they'll have to blast it again and start from scratch, if they've damaged the finish by blasting the first time then starting again is not going to resolve the problem.

[Mick BaileyParticipant @mickbailey28509]

Powder coating on magnesium is best removed chemically. Another issue with powder coating magnesium is trapped gas that expands when heated and cause the coated surface to bubble (outgassing) and creates a heavily cratered surface when cool. This may be the issue and is worsened by blasting. Be sure that the company has experience of coating magnesium – you can't treat it like steel or aluminium – the process is different.

[Sam SpoonsParticipant @samspoons83065]

#Mick Bailey, thanks. They did say they chemically stripped the old powdercoat off the frame and discovered the badly corroded finish underneath. I feel they should have contacted me before continuing but they didn't and seemed to want to hurry me out of the building when I collected it rather than encouraging me to check it over before I left. From what you say it sounds like they were not trying to fob me off which makes me feel a little better. Either way the bike is together and in use and, despite the less than perfect finish, looks great.. (as is my wife's).

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