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My aluminum bike (Cannondale Adventure 1) was scratched on the welds connecting the seat tube and seat stays, and I was wondering if the damage is purely cosmetic, or if there is any structural damage. The scratches on one side are deeper Deeper Scratch Deeper Scratch Zoom

and are shallower on the weld between the other seat stay and seat tubeShallow Scratch

I've gotten conflicting messages from my local bike shops. Some say it's totally fine, others say that this is serious and I should stop riding it. Unsurprisingly, the bike shop that caused this damage is one of the shops saying it's purely cosmetic. I would really appreciate your inputs!

Edit: Sent this pictures to a frame builder, who said that the damage is cosmetic. Very grateful to hear that, and honestly, I don't care about the cosmetic damage.

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    Aside - try going to one of those discount dollar stores and find the nail polish. For a few dollars you can get a bunch of metallic blue acrylic paints in their own jar with an applicator brush too. Great for touching up your bike when this kind of thing happens. I suspect my road bike has more nail paint than real paint by now.
    – Criggie ♦
    Commented Nov 1, 2023 at 6:14

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Cosmetic only. The stand clamp has munched on the paint/gel coat and put some scratches in the weld surface.

Annoying at worst but nothing structural.

Some light finger tip sanding and nail polish of an appropriate color will hide the worst of this error.

Maybe the bike shop will do the spot fix for you as compensation.

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    Suspect you might be right, but FFS - what did they do, my work-stand would not that close into the weld even after I removed the rubber protection bushes.
    – mattnz
    Commented Oct 26, 2023 at 8:48
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Bottom photo shows what are most likely cosmetic scratches.

The top photos look to me like the weld has failed - in which case the frame is unserviceable. If this is merely a scratch - how did it happen?

Consider the options - if you accept the frame is unserviceable, you (or someone else) buy a new frame and you continue to ride, worst case is you (or someone else) spend some money, best case is the same. If you do not accept the frame is unserviceable, you keep riding. Best case your riding enjoyment is tarnished with concern over the frame. Worst case is the frame fails and you have a nasty, life altering accident.

The dispute of liability and who should pay for the new frame is probably outside the remit of this Q&A and might be best asked on law.se. What I can suggest is you get an assessment and quote for a repair (probably requires new frame as aluminum bike frames cannot be welded easily) from a couple of shops, and seek compensation for the shop you believe is responsible though various legal means (Where I live we have a low cost/no lawyer dispute resolution service for low value things like this).

Personally, I would not ride on that frame.

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    With regards to how it happened, I was told by a local bike shop that the scratches were caused by a different bike shop incorrectly placing the bike on a stand when doing maintenance. They said that the bike shop should have clamped onto a different part of the seat tube and placed rubber between the clamp and the frame.
    – Peachy
    Commented Oct 26, 2023 at 2:02
  • If you're leaning towards frame replacement and are seeking compensation from a shop, it would nice to prove structural as opposed to cosmetic damage of the metal. Since you'd scrap the frame anyway, maybe you could use a scalpel/razor to fleck off some of the paint around the offending areas, particularly in the top pic where mattnz suspects weld failure, to get a clearer view of the metal and welds? I'm suggesting flecking paint, not sanding it off, since sanding can smear paint and metal powder into small cracks in the metal and obscure them.
    – SSilk
    Commented Oct 26, 2023 at 7:53
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    I won't change my answer, but the Frame stand explination, and @Warrens answer is a reasonable explanation of a mechanism that would explain this damage that makes it is cosmetic. (I won't go into my thoughts about the Bike mechanic who did this (if it is the case), except to say they are unpublishable). In this case, flacking off the paint to be certain makes a lot of sense.
    – mattnz
    Commented Oct 26, 2023 at 8:51

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