Powder coating

General cycling advice ( NOT technical ! )
JohnMorgan
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Joined: 9 Jun 2022, 7:19pm

Powder coating

Post by JohnMorgan »

Hi all,

Have a ‘blister’ on the seat tube of a powder coated, steel frame. Any knowledge of how to fix it?

I’m considering taking it off, filling and painting; ‘lifting’ it and re-attaching with pva; having the lot removed and starting again.

Has anyone had this problem?
Jdsk
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Joined: 5 Mar 2019, 5:42pm

Re: Powder coating

Post by Jdsk »

It's obviously crucial to protect against rust.

How much do you care about the finished appearance?

Thanks

Jonathan

PS: How old is the powder coating?
PH
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Re: Powder coating

Post by PH »

How long since it was coated? Can you take it back?
Rust under powder coating can be a problem, more so than with paint, mainly because it can get quite bad before it disturbs the coating.
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simonineaston
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Re: Powder coating

Post by simonineaston »

I don't want to rain of your parade, op, but successful powder coating is notoriously at the mercy of high quality prep. and one swallow does not make a summer, if you catch my drift... it might pay you to examine places subject to wear ie dropouts for signs of that the coating is flaking.
I've got used to this issue over the years as the finish on Pashley-era Moultons was a bit hit-or-miss. Having dealt with it by having one ro two frames refinished and absorbed the price hit, I settled on simply buying a pot of matching Humbrol enamel, not so much as their paint is high quality so much as for the ability to get a close colour match. I then rubbed down the areas where the powder coat flaked and hand-painted them - often with very good results. Much, much cheaper than a refinish.
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
JohnMorgan
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Joined: 9 Jun 2022, 7:19pm

Re: Powder coating

Post by JohnMorgan »

Many thanks for the replies, chaps. Already resorted to Humbrol enamel to touch up brazed on cable guides and the odd chip. The job is a few years old, happy with the quality of the work, but it’s my ‘sensible’ bike, and has a ‘hard paper round’ :-) I could have broken the finish swapping out front derailleurs, chainrings or any amount of spanner slinging. Not particularly worried about the odd fault, just trying to keep the frame on the road the right way up.
How successful is the ‘sand and paint’ remedy - does the powder coat feather successfully, or just peel off?
PH
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Re: Powder coating

Post by PH »

JohnMorgan wrote: 2 Jul 2022, 1:50pm How successful is the ‘sand and paint’ remedy - does the powder coat feather successfully, or just peel off?
More the later.
Also when sanding it'll be best to go till the patch is all rust free, until that's done you won't know how much needs repainting.
I never have much luck with invisible paint repairs so I've given up trying, I now do the opposite and paint a contrasting panel.
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simonineaston
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Re: Powder coating

Post by simonineaston »

The last two frames I used Humbrol on were i) simple black gloss and ii) brg. Both repairs looked great and lasted well. I would go so far as to say the repairs were both invisible! One frame I sold, and I'd pointed out the paint repair to the buyer ahead of the transaction... once it arrived, he said he was perfectly happy and couldn't spot the repair.
However, I'd add that those two colours are exceptional in that they were easy to get an exact match for.
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
elmo
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Joined: 11 Aug 2009, 1:08am

Re: Powder coating

Post by elmo »

I now avoid powder coating where I possibly can. The factory that I worked in went over to powder coating in the mid 80's. It is cheap and it is simple. My factory made components for the motor industry so the parts all had a relatively short life span hence the longevety of the paint coating did not really matter. I have since lost count of the domestic items I have had where the powder coating has just peeled off. I repainted a workmate tool box last year. The powder coat simply peeled off when placing a pen knife blade under the lifted paint surface.
Unless the to be painted surface is totally clean and grease free the powder once heated lifts from the metal surface. The metal rusts from within. Once the powder coating has started to lift the metal underneath is coated in rust. Powder coating is cheap and cleaner than liquid paint which is why it is used alot in industry.

With regatrds to humbrol, long before airfix came along they made their paints to touch up bicycles. All their early colours are exact matches for cycle paints of the day.
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simonineaston
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Re: Powder coating

Post by simonineaston »

made components for the motor industry so the parts all had a relatively short life span
That's an interesting snippet - can you tell us more about that idea, elmo? That is, the type of components, materials used, intended life, how it's worked out how long they should last, and so on.
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
gxaustin
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Re: Powder coating

Post by gxaustin »

I had the spoked wheels of my car powder coated about 27 years ago, because the paint was getting rust spots coming through.
80,000 miles later and the wire wheels are still serviceable.
On the other hand I used Humbrol orange to touch up the orange paintwork of my bike frame - and now its pale pink.
Dingdong
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Re: Powder coating

Post by Dingdong »

I've always went for black or signal red for powder coated frames, as above they are the easiest colours to get right. Where you have compression on a bike: drop outs, seat clamp, front derailleur, you'll always get chipping and flaking of the powder coating, the secret is to nip it in the bud early and refinish it, preferably with a rust seal before you paint.
rogerzilla
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Re: Powder coating

Post by rogerzilla »

There is good powdercoating where the frame is phosphated and primed before the actual plastic powder goes on, but most is just onto bare metal. The latter is very hit or miss and only works well if the metal is blasted immediately before coating. My local cowboys even trap blasting grit under the coating, and they are still better than most!

These guys do it properly:
https://ctc-powder-coating.co.uk/our-work/bicycles/

BUT it will cost you about the same as a wet paint job at a framebuilder.
Jamesh
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Re: Powder coating

Post by Jamesh »

I'd get a razor blade and lift the blister, clean the blister / frame with fine sand paper and glue back on with epoxy glue.

Put some duct tape over it until it hardens!
JohnMorgan
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Joined: 9 Jun 2022, 7:19pm

Re: Powder coating

Post by JohnMorgan »

Good to know :-)

Looks like I’ll try to ‘Humbrol’ it, then become more dramatic if that does’t work out.

My thanks for your input :-)
JohnMorgan
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Joined: 9 Jun 2022, 7:19pm

Re: Powder coating

Post by JohnMorgan »

OK. The powder coating came off fine, rust gone, paint on, lacquer on, will give it the once over with T-Cut today and post some pictures.

Paint a bit lighter shade than the bike, but can’t be helped. In the course of applying coats I tried a black coat followed by the green, which toned it down a touch, but subsequent coats brought the original tone back.
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