Preventing rust and protecting paintwork

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  • Hi all. Just working on my latest project and wanted some advice on the paintwork. Generally the paint is in reasonable condition (it’s an 80s Harry hall) but there are signs of surface rust peaking through in a few patches. It’s not too bad but any advice on how to clean it up and prevent it from deteriorating? I will be keeping it in a cycle loop hanger so it’s kind of exposed to the damp even if it’s not getting wet when it rains and even in the last few weeks it’s got a little worse. Thanks in advance!

  • Some images of the emerging spots

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  • I've never used it myself but an oil called owatrol penetrates the paintwork and protects. Might be useful.
    Also internal rustproofing is recommended too dinitrol is good stuff.

  • Thanks - when you say internal do you mean inside the tubes?

  • I’d add that I read somewhere t cut is good but welcome anyone’s experiences with that

  • Yes inside...often rust works from the inside out.
    There is a product called frame saver but dinitrol is cheaper and just as good if not better.

    T cut is a polish and will improve and level (appearance) of the paint work but will not add protection.

  • Looking to treat some rust on my Roberts frame. Looking for advice on best method. There are some sections where the paint has completely gone and there is a fair bit of rust. I imagine the rust would need to be sanded off before treatment. The rear mech hanger is also raw as it was heated and bent back into line after a crash. Not sure if clear coat alone is all I need.

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  • I would put kurust on that and just keep an eye on it

  • The pink finish on that fork crown looks like powder coating (rather than stove enamel) - one thick layer which peels off in big chunks when water gets under it. It would probably need to be stripped chemically, not shot blasted, especially if it's light tubing.

    No need to panic about the loss of finish from the crown itself since it's a casting, but severe rust on the blades would be more worrying.

    I agree with Dogtemple's suggestion of Kurust - the main ingredient of this product is phosphoric acid, so you are effectively phosphating the steel, which is an excellent pretreatment for paint.

  • I’d get rid of the loose powdercoat asap, water will get under it and rotting whatever it’s in contact with.

  • Thanks for the responses.

    Basically, I've got no idea what I'm doing when it comes to paint. so it when you say chemical treatment and getting rid of loose powder coat sounds like i might be better off getting a professional job done.

  • It’s definitely an option. Depends what outcome you want.

    Doing it yourself it’s going to be pretty difficult to get a decent finish. Stripping powdercoat that isn’t loose and flaking is a tough job.

    If a ratty finish will suffice then a wire brush will remove the loose powdercoat and rust. A wire wheel/cup on a drill will do it quicker. Lacquer over the exposed steel will keep the rust at bay for a short while, rust converter, primer and paint will keep it good for longer.

  • All you need to do is chip off the loose paint with a screwdriver. Clean any dirt and rust off with a toothbrush or wire brush if you have one and slap on some kurust (chemical treatment). It will take you a few mins, it is so far away from needing to be taken to a pro.

  • I agree with both of the two posts above, but I'd just like to add......


    Or 'clear coat' as it's sometimes called here. As M_V says, this not good rust protection. In the '90's, when I still worked in the finishing trade, there was a fashion for lacquering bare steel (any kind of object, not bikes particularly). At first we would take these jobs, degrease and finish with stoving lacquer as requested, but the customers came back complaining of rust so often that, in the end , we refused to do this work. BTW none of our other jobs went rusty.

    Powder Coating

    In general this is a good example of the twin modern curses of de-skilling and skimpflation.

    It's de-skilling because any fool can get a reasonable result with powder, whereas wet paint needs some skill and aptitude to get a good finish. So if you've got a decent paint sprayer you need to hang on to him and treat him well, but if you just want some one to apply powder, almost anyone will do!

    Skimpflation: A recent word for me, but I've been aware of it for years. In order to maintain or increase profit, the quality of a product is reduced, usually in a way which is hidden from the consumer. Think of all the branded goods that used to be made in Britain but are now made in the far east. They may look the same, but the quality is poor and they usually break at the end on the guarantee period.

    Powder coating as compared to stove enamel is an example of this process, especially when it comes to bike frames. If you're making a cheap utility bike (which will probably not be used, rapidly becoming just shed clutter) powder coat is fine. If you're making a quality lightweight which is going to see hard use and possibly last for decades, you need stove enamel. Otherwise you'll get the same result as that pink frame further up this thread.

  • There’s a definite stigma around clear coat amongst framebuilders and the like but imo powdercoat is a lot worse.

    When my mate discovered cracks in two of his frames within a week or so I don’t think it was coincidental that both had been powdercoated.

    I’ve got a frame in for 2 new chainstays and it’s been powdercoated.

    At least with clearcoat you can see what’s going on underneath, powdercoat is too good at hiding things.

  • Is this sort of rust working from the inside working it way out? Or start on surface?

  • It’ll be from the outside I’m sure. Definitely on the crown as that’ll be a solid casting.

    I think the water gets in through a nick in the powdercoat or at an edge and has its evil way.

  • Question on clear coat please. I have a 70’s frame with original paint but the clear lacquer finish on the original blue paint is very soft & turns powdery with any sort of friction / contact. I was thinking clear coating over the original paint seems like the obvious solution?

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  • It's a surprising thing about lacquer (clearcoat, varnish - call it what you like), you can rub it down, which makes it look 'milky' and then overcoat with more lacquer and the milkiness will disappear, giving (with any luck) a good result.

    In this case you will have to touch in where the blue has gone through to the light coloured under coat. Use fine wet and dry paper (minimum 400 grit, 600 would be better) to flat the old lacquer, and use it wet.
    Try to be careful not to break through to the undercoat, and do a small trial area first - it's possible the new lacquer could react with the old.

    Remember also: the glossier the finish, the worse any defects will look. A possible alternative would simply be to wipe over it with an oily rag.

    Good Luck!

  • I think the water gets in through a nick in the powdercoat or at an edge and has its evil way.

    Yes, I think you're dead right about that. I suspect this frame was shot blasted and then coated with no pretreatment at all. A quick spray with yellow etch would probably have prevented this, as would phosphating. But that's skimpflation for you!

  • I have thought in the past about whether it’s possible that the texture that’s created by aggressive blasting could also aggravate the problem, like it creates more surface area than a polished or mill finished tube.

  • Thanks! Will give the oily rag a go first, I’ve only just just built the frame up so it’s a little annoying to have to strip all the parts off & resolve the lacquer issue. The white marks under the white brake cable on the top tube isn’t actually a lighter colour under coat its where the lacquers turned milky white & does disappear with a bit of spit & finger polish.

  • it’s possible that the texture that’s created by aggressive blasting could also aggravate the problem

    'Agressive' blasting certainly can cause problems.

    'Shot blasting' itself is, in practice, a vague term because it's used to cover blasting generally but there is a wide range of blasting media which all give different results - examples: sand, chilled iron, glass beads - there are many others.

    If you are* a large scale manufacturer of steel bike frames you could choose the ideal medium for the job, but if you're an artisan frame builder you will probably be looking for a small scale metal finisher ( a stove enameller) who finds it worthwhile to do a few bike frames. The stove enameller may have to put out the blasting job to some one else, but even if he's got his own blasting plant, he won't go to the trouble of changing the medium just for a couple of bike frames. I may be a bit out of date here talking as though there exists a number of finishers to chose from. In the Borough of Richmond in, say, 1980 there were at least five different stove enamellers, now there are none. However, the principle remains the same - blasting plant is quite expensive to buy and run, it's a big ask to find just the right set up to do bike frames, a job which is never going to contribute much to the overheads.

    A further problem is that blasting is a terrible job - hot, deafening, boring, dirty and usually not well paid. To say that the people who do it are gorillas would be, in most cases, rude to gorillas.
    So don't expect your frame to be handled with the loving care that you would hope for. It's not rare for blasting to create holes - in one case I saw some one had managed to blast a hole through a cast bottom bracket shell.

    Back to M-V's orginal point that blasting 'spreads' the surface, this is correct and it's notable that if you blast mild steel sheet it goes from flat to curved - when you blast the second side of the sheet, it goes back to more or less flat. So yes, it must create some stress in the tubing, but with a newly brazed frame it is essential to remove the flux before painting, so something has to be done. Probably the best answer is to blast with something soft, like glass beads - Reynolds forbade heavy blasting of 753 tubing and recommended (as I recall) glass beads.

    Finally, if you want to rechrome don't blast those areas, because chrome must be done on a polished surface, and it's next to impossible to polish a shot blasted surface.

    • Of course, this should be past tense in the case ofthe UK!
  • Is chemical stripping better? I've also heard that blasting leave an ideal surface for painting.
    I was thinking of powders coating a frame recently but have been told it can be a bit thick and not a good look on a old lugged frame.
    All very confusing.

  • That’s interesting what you say about blasting warping sheet steel. That could definitely be part the reason for post powdercoat chainstay failure.

    The last powder coater I used was at the cheap and dirty end of the spectrum. I stopped using them when they bent a rack I’d made almost in half and denied responsibility. I’d noticed on areas they’d blasted but not coated that the steel was very heavily textured so suspect they were using too harsh a medium or just going at it too hard.

    You also made a good point about the lack of anti corrosive. There’s nothing about powder coat itself that inhibits corrosion so a separate treatment would be nice but I’ve not heard of any powdercoater offering this.

    I’ve been using a zinc rich primer when I’ve been painting frames and I know most painters/enamellers have their own things they’ll do to add some protection.

    @wildwest, I’d have thought chemical stripping was a better way to go yeah, the only problem with that is that I understand it’s now very difficult to get hold of chemical strippers that are effective thanks to regulation of the active ingredients. I don’t think there’s much out there that’ll have much effect on powdercoat.

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Preventing rust and protecting paintwork

Posted by Avatar for Sheggers @Sheggers