surface rust vs pitting - how do they differ/look ?

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hoogerbooger
Posts: 222
Joined: 14 Jun 2009, 11:27am

surface rust vs pitting - how do they differ/look ?

Postby hoogerbooger » 6 Jun 2020, 5:00pm

I ask as I've read in a few places that surface rust on a steel frame may be controllable without rubbing back down to the metal. Whereas if it's pitted it's definitely a rub down to the metal, then various steps of prep before repainting locally ( or spend some dosh on a proper re-spray)

However I haven't found anything to date to help distinguish clearly surface rust vs pitting.

The paintwork on my Raleigh Randonneur is in most areas fine, but looks like it has localised areas of pitting on the rear stays & a couple of areas where there is a little rust visible at the surface but with a few raised lines in under the paint.

I attach some pictures. My question is: Is the rust on the front fork surface rust ? or gone beyond that.

( In principle I have Scottish blood and like to see if I can fix things myself. In practice I am probably prepared to spend the dosh if I have to and I don't want the rust to go too far. But obviously it'll just then get scratched, or stolen cos it looks pukka)
Image Attachments
Rust 3.jpg
Rust 2.jpg
Rust 1.jpg

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531colin
Posts: 13417
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: surface rust vs pitting - how do they differ/look ?

Postby 531colin » 6 Jun 2020, 5:52pm

The corrosion is under the paint, which suggests to me the paint needs to come off.
The wiggly lines are filiform corrosion, I think.

Steve O'C
Posts: 93
Joined: 3 Mar 2013, 1:32pm

Re: surface rust vs pitting - how do they differ/look ?

Postby Steve O'C » 6 Jun 2020, 6:17pm

I also have a Raleigh Randonneur and noticed that I had a similar problem with the front forks. The rest of the frame is fine. I took to the forks to Coloutr-Tech a couple of days ago to get them re-sprayed.

https://www.colour-tech.co.uk/

Dave took out a scalpel and scraped off the paint which seemed to show that it was surface corrosion rather than corrosion from inside the forks. He commented that there appeared to be no primer underneath the top coat. I wonder if that is why the forks have corroded but the rest of the frame is fine. Is it possible that they produced a batch of forks that did not have a proper primer?

Steve

PS I have no connection to Colour-Tech and I have not got my forks back yet so I am not particularly endorsing this business but the finished frames he had there waiting for collection looked fantastic.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: surface rust vs pitting - how do they differ/look ?

Postby Brucey » 6 Jun 2020, 8:21pm

531colin wrote:The corrosion is under the paint, which suggests to me the paint needs to come off.
The wiggly lines are filiform corrosion, I think.


I agree. However there is also a thing on one of the stays that looks more like a 'blister'. This is more worrying to me; I have occasionally seen such things when a tube has corroded through from the inside.

To ascertain the nature of the corrosion the paint has to come off. If you just want it not to get much worse whilst you are thinking about it, then you can slap a load of corrosion inhibitor (eg waxoyl) on the affected parts, both inside and out. This won't always entirely stop filiform corrosion though.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

hoogerbooger
Posts: 222
Joined: 14 Jun 2009, 11:27am

Re: surface rust vs pitting - how do they differ/look ?

Postby hoogerbooger » 7 Jun 2020, 9:28am

I shall take it for a ride and reminisce about past travels. Then I shall investigate those raised blisters.

( Holby City time WARNING this may contain upsetting scenes involving rust and tears as a grown man is forced to open his wallet)

Sounds like whatever it's going to be a respray as overall seems too much for local repair. Argos is my nearest, so I will probably see if they can paint match get decals etc.

But are small rust holes fillable by a frame builder ? Rather than stay/tube replacement

JakobW
Posts: 423
Joined: 9 Jun 2014, 1:26pm
Location: The glorious West Midlands

Re: surface rust vs pitting - how do they differ/look ?

Postby JakobW » 7 Jun 2020, 9:44am

I'm sure I've seen pinhole repairs done in the past, whether with brazing metal or by brazing a plate on top, but I don't think I'd trust it for a lightweight tube - unless it was really localised corrosion, I'd assume it was going to go elsewhere sooner of later.

Greystoke
Posts: 397
Joined: 8 May 2018, 7:41am
Location: Lincolnshire

Re: surface rust vs pitting - how do they differ/look ?

Postby Greystoke » 7 Jun 2020, 9:59am

I've restored many cars and so I think I know a thing or two about rust.
If it's started on the inside and is now appearing on the outside it's worse than the bit you can see.
Everything is repairable but some things are easier and cheaper than others.
Note I realise frame material and car bodywork whilst still being metal are different.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: surface rust vs pitting - how do they differ/look ?

Postby Brucey » 7 Jun 2020, 12:53pm

Note that 531 chainstays are pretty thin (some builders won't use even ST ones in heavy-duty builds) so if rust has come from the inside then you should probably be 'very concerned'.

OTOH if a chainstay starts to crack it isn't that likely to kill you; the main danger is annoyance if you have the frame repaired/ refinished and then it breaks.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

hoogerbooger
Posts: 222
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Re: surface rust vs pitting - how do they differ/look ?

Postby hoogerbooger » 7 Jun 2020, 8:46pm

(THE FOLLOWING POST CONTAINS GRAPHIC IMAGES)
(Apologies in advance to good bike owners)

I inspected again and found worse rust ! So stripped the bike. Clearly the 37mm back tyre (now binned) +mud had been rubbing the stays and it looked rather worrying, particularly on one side. Bridge was bad as well.

worst rust 1.jpg

So I've removed the paint and had an initial sand and inspection of the worst locations:
worst rust 2.jpg

Bridge.jpg

The rust hasn't come from the inside and wouldn't seem much metal gone. Prodded and squeezed and no give, but there remain what I presume are pits on these worst bits that were below blisters. Bottom bracket is mostly spotless inside, with a tiny bit of rust at the braze area on the inside of the stays, at the bottom side, but no sign of rust beyond in the bit you can poke a finger into. ( someone needs to make a bike frame endoscope attachment for a smartphone) All tubes I could see into have no rust.

The pits don't seem deep and my presumption is the frame isn't dead.

Presuming that is the case I will do a temporary local repair of these areas. But with a proper respray after the summer.
( In Wales we are still on lock down .......I did wonder if the Heddlu would consider a drive to Argos in Bristol an essential journey. Seem to be plenty of English motorcycles here driving to the supermarket in Brecon to buy a sandwich)

more sanding/glass fiber penning to go, BUTwith the pits and surrounding metal , is it remove all rust then Kurust. Then just used Humbol enamel in thin layers allowing for curing time ? The objective is just to contain until the respray.

Brucey
Posts: 43049
Joined: 4 Jan 2012, 6:25pm

Re: surface rust vs pitting - how do they differ/look ?

Postby Brucey » 7 Jun 2020, 9:07pm

it doesn't look that bad to me. Kurust and any paint will hold it for a while. So would waxoyl.

If you want to tart it up, Kurust, good primer and then a topcoat.... I think 'Peugeot graphite grey metallic' is not a million miles from being a good match, if that is the colour I think it is;

Image

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

RobC
Posts: 135
Joined: 5 Feb 2008, 3:27pm

Re: surface rust vs pitting - how do they differ/look ?

Postby RobC » 8 Jun 2020, 1:56pm

Steel frames are very forgiving in terms of rust- as long as it’s not come from the inside out - and are not super thin walled, as others have mentioned.

Here’s Some before and after pics of my grandparents’ 1930s tandem when I fished it out of the cellar and at the nearly-completed renovation. frame was blasted and the worst of the pitting filled and smoothed
Image Attachments
8A7B44FF-6E97-4BA1-BAD5-A6A542016607.jpeg
3F468F2D-0610-4BBF-8736-8F64FDC16B80.jpeg

mig
Posts: 2346
Joined: 19 Oct 2011, 9:39pm

Re: surface rust vs pitting - how do they differ/look ?

Postby mig » 8 Jun 2020, 2:11pm

hoogerbooger wrote:I ask as I've read in a few places that surface rust on a steel frame may be controllable without rubbing back down to the metal. Whereas if it's pitted it's definitely a rub down to the metal, then various steps of prep before repainting locally ( or spend some dosh on a proper re-spray)

However I haven't found anything to date to help distinguish clearly surface rust vs pitting.

The paintwork on my Raleigh Randonneur is in most areas fine, but looks like it has localised areas of pitting on the rear stays & a couple of areas where there is a little rust visible at the surface but with a few raised lines in under the paint.

I attach some pictures. My question is: Is the rust on the front fork surface rust ? or gone beyond that.

( In principle I have Scottish blood and like to see if I can fix things myself. In practice I am probably prepared to spend the dosh if I have to and I don't want the rust to go too far. But obviously it'll just then get scratched, or stolen cos it looks pukka)


i wouldn't be overly concerned about riding that frame. my geared commuter has similar (but the patches do get some ACF50 from time to time.) i'd be more worried about the state of your chain :D

bgnukem
Posts: 607
Joined: 20 Dec 2010, 5:21pm

Re: surface rust vs pitting - how do they differ/look ?

Postby bgnukem » 8 Jun 2020, 2:50pm

General corrosion is less damaging than pitting, but the only way to be sure there isn't any pitting is to remove the paint and all superficial corrosion from the affected area, so then you are already committed to rust conversion/re-painting.

Filiform corrosion is usually pretty superficial and I wouldn't go to the trouble of repainting unless it continues to spread.

Pitting is worse because a 'concentration cell' can form under a semi-permeable cap of paint/rust and the accumulation of corrosion products within the cell creates a far more acidic/aggressive environment therein vs. the external environment, leading to rapid corrosion (and greater depth of penetration) despite looking fairly innocuous on the outer surface of the tube.

If the tube's perforated from the inside out though I'd be tempted to scrap the frame, as you'll never be sure how much of the remainder of the tube wall is paper-thin and about to fail.

hoogerbooger
Posts: 222
Joined: 14 Jun 2009, 11:27am

Re: surface rust vs pitting - how do they differ/look ?

Postby hoogerbooger » 8 Jun 2020, 9:45pm

When I posted the pictures I thought do I clean the chain as there is bound to be someone who will comment :shock:

VERY impressed with the tandem saving.

Having fun here on localised repair of the worst bits.

(When I was a teenager I had one bike and completely dismantled, cleaned,serviced about 4 times a year, ..for fun as much as anything. Was no rust on that bike and spotted things before they became a problem. Too many bikes and too many other things to do now. 100 lines for me. I must clean my chain and do better)

hoogerbooger
Posts: 222
Joined: 14 Jun 2009, 11:27am

Re: surface rust vs pitting - how do they differ/look ?

Postby hoogerbooger » 22 Jun 2020, 4:12pm

Ok have repainted the worst bits of rust. But that still leaves some acreage of filliform rust on the lower stays and lower fork.

I can waxoil these, but as I understand it that will slow but not stop it.

Presumably waxoiling the inside of the frame is not sensible if I'm going to get the frame resprayed this or next winter? Leave that until after?