Paintwork problems

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trevorcox
Posts: 6
Joined: 12 Oct 2015, 9:31pm

Paintwork problems

Postby trevorcox » 5 Feb 2020, 7:35pm

I was surprised to find the paintwork under my 853 tourer has suddenly deteriorated. Viewed from above it is in pristine condition. I had this resprayed about 7 years ago. Any ideas what the black spots are:
paintwork1.jpg

And what can have caused the sudden rusting? It doesn't get put on a car rack or anything that would have rubbed the underneath paint. The problem isn't just under the bottom bracket, it is also on the bottom of the chainstays near the axle.
paintwork2.jpg

AndyA
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Joined: 21 Mar 2009, 9:16pm
Location: Edinburgh

Re: Paintwork problems

Postby AndyA » 5 Feb 2020, 9:56pm

I guess it was pretty rusty before the respray? It's very hard, bordering on impossible, to remove all of the rust from all of the pitting. A possible explanation is that the previous rust has re-established itself and has started to lift the new paint up.
I'd treat it with waxoyl or similar and think about respraying in the next few years

alexnharvey
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Joined: 10 Jan 2014, 8:39am

Re: Paintwork problems

Postby alexnharvey » 5 Feb 2020, 10:22pm

The black spots are probably black iron oxide, Fe3O4.

Is there a drain hole in the BB shell? Exterior rust is an irritation. Interior rust in a poorly drained frame can be terminal.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Paintwork problems

Postby Brucey » 7 Feb 2020, 4:56pm

marks in the top photo look alarmingly like the tube is rusting from the inside, and you might have a couple of pinholes which have broken through.

It has been a very wet autumn in most of the country; all kinds of things have been wet for weeks on end and have rusted this year when they have not in previous years.

I hope the damage isn't as bad as I fear it to be.

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

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willcee
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Location: castleroe,co.derryUlster

Re: Paintwork problems

Postby willcee » 9 Feb 2020, 11:25am

I would agree with Brucey, however imo the 7 year old repaint wasn't a good 'un as i for one cannot see any sign of a light grey primer in that bracket underside which would normally be used under a silver top coat.. nor has there much sign of a decent depth of paint.. will

David9694
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Joined: 10 Feb 2018, 8:42am

Re: Paintwork problems

Postby David9694 » 10 Feb 2020, 12:22pm

Salt spray a factor here?

Marcus Aurelius
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Joined: 1 Feb 2018, 10:20am

Re: Paintwork problems

Postby Marcus Aurelius » 10 Feb 2020, 12:36pm

The black spots in the first photo are the work of the ‘metal worm’ the tube is rusting from the inside out. That’s not good news. The reason for the ‘patina’ on the frame is almost certainly road treatments ( salt / grit ) corroding the surface. Road treatments contain molasses, in order to stop it just getting blown away, removed by traffic, before the ice formation it’s supposed to prevent, has tried to form. This makes it sticky, and it’s a bugger to get off a bike frame. That leads to corrosion issues on steel / some other alloy frames. Carbon frames don’t suffer the same issues, ergo Carbon is better than steel.

bgnukem
Posts: 242
Joined: 20 Dec 2010, 5:21pm

Re: Paintwork problems

Postby bgnukem » 10 Feb 2020, 12:43pm

853 tubing is also very thin I believe, maybe 0.4mm wall thickness mid-tube-length. If you have internal corrosion which has penetrated the tube wall I guess you might be looking for a new frame....

If you stop the rot no reason why a steel frame can't last. My Dawes is 25 years old ridden as a winter bike in all weathers and I've never allowed any rust to get started, any stone chips are touched up immediately and the tube internal surfaces have been flooded with waxoyl twice. The bike is stored in a dry environment.

When the frame eventually dies it will be due to metal fatigue and not corrosion....

David9694
Posts: 391
Joined: 10 Feb 2018, 8:42am

Re: Paintwork problems

Postby David9694 » 11 Feb 2020, 9:40am

Marcus Aurelius wrote:That leads to corrosion issues on steel / some other alloy frames. Carbon frames don’t suffer the same issues, ergo Carbon is better than steel.


You weren’t expecting to get away with that, surely?

David9694
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Joined: 10 Feb 2018, 8:42am

Re: Paintwork problems

Postby David9694 » 11 Feb 2020, 10:22am

So it looks like we might have in the brown corner exterior rust, and the black corner, interior oxidisation (same thing?)

The least your paint sprayer can do for you at this stage is supply some matching paint.

I’d have a look at the inside of the b/b shell and see what light you can shed on the interior rust as a first step. I’d be inclined to clean off the paint around the two chainstay pinpricks and again see if that sheds light on the “metal worm” diagnosis.

I’d look to clean the outside b/b shell rust away back to shiney metal with a view to re-coating, assuming you can shift the b/b, Clean up the interior, obviously taking care not to damage the threads, although if there is corrosion these might be best being recut.

I’ve never used Waxoyl, but presumably the idea is to hang the frame up by the head tube and pour it on in to the headtube and b/b to coat the insides of the frame?

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NATURAL ANKLING
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Re: Paintwork problems

Postby NATURAL ANKLING » 11 Feb 2020, 10:50am

Hi,
The black spots you could probably put your thumb through in that case the frame is a scrap.
I don't like waxoyl either, probably because I've seen too much of it dripping off the underneath of cars that are also rusted through.
Probably because it was put on or in too late to have any affect on the rust.
On cars I cut the rust completely out, weld and then paint.
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peetee
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Joined: 4 May 2010, 10:20pm
Location: Cornwall

Re: Paintwork problems

Postby peetee » 11 Feb 2020, 11:28am

I am far from being an expert on paint and corrosion but I believe the frame has been badly prepared before spraying. It is vital that all work is done in low humidity and the frame is totally free of contaminates before painting. I suspect the black spots may be something other than moisture, likely oil or grease contamination. Thick patches of chain grease that weren’t completely removed perhaps? The bottom bracket problems support that idea as it’s just the sort of area that collects a really stubborn concoction of road muck and chain lube. Add in a degree of rusting under the original paint finish and whoever prepped that frame should have been really thorough.
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mercalia
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Joined: 22 Sep 2013, 10:03pm
Location: london South

Re: Paintwork problems

Postby mercalia » 11 Feb 2020, 12:31pm

Brucey wrote:marks in the top photo look alarmingly like the tube is rusting from the inside, and you might have a couple of pinholes which have broken through.

It has been a very wet autumn in most of the country; all kinds of things have been wet for weeks on end and have rusted this year when they have not in previous years.

I hope the damage isn't as bad as I fear it to be.

cheers


I thinkI can see a pin hole in one of the spots?
also a very poor paint job just one layer?

bgnukem
Posts: 242
Joined: 20 Dec 2010, 5:21pm

Re: Paintwork problems

Postby bgnukem » 11 Feb 2020, 12:59pm

Stick a pin in the pinholes,

If it goes through try a philips screwdriver.

If that goes through - new frame time.....

mercalia
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Location: london South

Re: Paintwork problems

Postby mercalia » 11 Feb 2020, 1:34pm

I really wonder at the virtue of these fancy steels that use such thin tubes, for durability. When my 531 Dawes Horizon frame was trashed I was surprised how thin those tubes where, so goodness knows about 631 and 853. Condensation inside tubes is hard to avoid?