Paint bubbles on top tube

I have a 3T Strada that was custom painted by my LBS (I bought this last year and my LBS couldn’t get a hold of the color I wanted, so they arranged to get a ready-to-paint frame for the same price and paint it themselves). I love the end result, but I have noticed a few bubbles in the paint near an opening at the top tube.

The bluish-white reflection to the left of the screw is from my iPhone’s flash. You can clearly see three bubbles. Is the cause just sweat ingress? And if so, is this something that can be remedied? Or something that can and should have been prevented when paining the frame?

I really hate that this happens in an area that is very much visible and I feel like is not a fault of mine: sports equipment should be able to deal with sweat. I realize that indoor training can be harsher in some respects, but still.

Do you have any advice? Are there other durability issues I should keep an eye out for?

If the LBS painted it, they can sand it down and fix it.

Don’t think that’s sweat ingress, sweat would also make the bolt rust. Probably just a bad paint job in that area.

I did have a few bolts (including the top cap bolt) replaced with stainless steel bolts because of sweat ingress. There is some sign of oxidation on the screw for the hose cap, too.

Basically, I’m a noob when it comes to custom paint jobs. I’ve already sent pictures to my LBS and the owner told me it is likely sweat ingress, which crystallized and expanded. I don’t know how plausible that is, but part of me thinks that (1) this is something they should have thought of when painting this (the factory paint jobs don’t seem to have this problem) and (2) this was an expensive bike. It is literally the most expensive thing I have ever bought.

Isn’t this a carbon frame? I don’t see how sweat could get in there and expand that much.

The likely conclusion is that they didn’t do the greatest job with prep and priming before painting.

I would not accept that this is your fault in any way. You should be able to sweat on a bike or wash or ride it in the rain without the paint bubbling.


If it was the paints fault, the paint wouldn’t have stuck there in the first place. Paint shrinks, it doesn’t grow. Paint is also super thin, so you would feel it as such. Did they paint over a sticker? I’m thinking the paint line is too early and that black bracket is pushing it back - with moisture getting in there. Is that just a cable bracket? They loosening it a touch for a few days.

Yes, the frame is fully carbon and apart from sweating on it on the trainer, I’m not doing anything.

I wipe my bike after each workout and keep towels on the handlebars (I had problems with rusted shifters on my previous bike, because I didn’t). But I take good care of my equipment without babying it. I’m totally ok with signs of use, but I agree, this shouldn’t happen.

There are other places where the paint shows signs of wear (around the dropouts) and in one, two places a small bit broke off (e. g. where the hydraulic hose for the front brake enters the fork). But these bubbles are directly in view and seem harder to fix.

I guess I will have to have a hard conversation with the shop then.

Yes, it is just a cable bracket/cover for the internal cable guide. It for sure isn’t a load-bearing part. The frame came with different ones, depending on what kind of groupset you have (e. g. another one has two holes to accommodate mechanical shifting in the rear). For reference, it sits just behind the head tube.

You’re probably getting corrosion there. The AL cap is coming into contact with some carbon. The sweat isn’t helping. They probably sanded past the outer layer of resin there prepping the bike.

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Thanks for the info. I’ll talk to them again. I get the feeling they aren’t very much inclined to fix it for free. Ugh.

If I was guessing I’d say they’ve had a screw in the hole whilst prepping/painting, to stop the threads getting clogged up, and maybe not went close enough to the screw hole with panel wipe/prep work/primer.

what does it look like under the little cover?

I tried to open it, and it wouldn’t open. My LBS (the one who painted the frame) told me they cannot do anything, unless I want to see naked carbon instead. Yikes. Next time I have a custom paint job, I’ll probably ask someone else … or just get a regular color (which wasn’t an option at the time due to Covid and supply constraints).