Spotty carbon stays

AussieRob said:

Hi guys – got a alu. bike with carbon stays. The stays have tiny white spots around the joins and stress areas (no its not salt from the road). I did a tap test and they seem okay, I haven’t noticed any issues with the bike (no cracks , handling issues or sounds) but it does have a lot of miles on it.

Anyone seen this before? Structural?

Thanks

rob

Could be moisture under the clear coat, if you depress the areas do you see the patch changing shape like a bubble flattening out. (it's difficult to describe). Or it could be just overspray or dust trapped under the clear coat during the painting process.

Do the 'spots' wipe off?

Back in the day when aluminum Vitus frames were coming unglued at an alarming rate, white powder was usually spotted at the joint prior to it failing...dried adhesive material working its' way out of the joint.

Are the spots under the clearoat? Perhaps just some poor adhesion in the clearcoat or outgassing lifting the clearcoat?

[font=Times New Roman]Thanks guys - appreciate it[/font]

[font=Times New Roman]The spots don’t wipe off and I can’t feel anything on the clear coat. The spots are not really bubbles (it’s not moisture) they are more like pin [censored], but there is no hole in the clear coat.[/font]

[font=Times New Roman]I know it’s not dust inside the frame because I have had the frame since 2002 and the spots are new.[/font]

[font=Times New Roman]Thanks again[/font]

[font=Times New Roman]rob[/font]

AussieRob said:

[font=Times New Roman]Thanks guys - appreciate it[/font]

[font=Times New Roman]The spots don’t wipe off and I can’t feel anything on the clear coat. The spots are not really bubbles (it’s not moisture) they are more like pin [censored], but there is no hole in the clear coat.[/font]

[font=Times New Roman]I know it’s not dust inside the frame because I have had the frame since 2002 and the spots are new.[/font]

[font=Times New Roman]Thanks again[/font]

[font=Times New Roman]rob[/font]

White material around carbon and aluminum is often corrosion. It can be coming from the area around the aluminum/carbon joint.

don't people say that carbon breaks without any previous visual-alert ?

Because carbon has essentially zero elongation and is composed of many layers, yes it usually fails without any visible indicators. That is, it won't bend or deform first. And any cracks are usually on inner layers where you can't see them.

This is different - a joint between carbon and another material. The failure modes avastly different and what was described could be a corrosion product, which could lead to a failure of that joint.

John Swanson
www.bikephysics.com