samkl 

Here’s a mystery. I installed Honjo fenders on my bike earlier this year. Occasionally when I went into the basement to retrieve my bike, I’d find some sticky oily film on them, almost like chain lube dripped on them. It was a little strange but I’d wipe it off and not think anything of it.

But a couple months ago, after not riding the bike for a while, I noticed this gunk on them again and wiped them off. But when I wiped it off it was too late—the substance had apparently damaged the aluminum, etching little lines in it. Now my fenders have these squiggly blemishes on them and I can’t get them out.

On the front they’re behind the fork, on the rear they’re in front of the seat stays.

What’s causing this? Excess Frame Saver dripping out of the frame? Could that damage aluminum? None of the other shiny AL parts on the bike are affected. FWIW I store the bike on a hook vertically, sometimes by the front wheel sometimes by the rear.

unterhausen

That's weird. No idea what the substance is other than maybe framesaver? I wouldn't think framesaver would do that.

I recently found one of my socket wrenches had some clear film on it and it was gummed up. No idea how that happened, but it did seem to affect the chrome in one place.

delbiker1 

It seems to me that most likely, whatever it is, leaving it there for a length of time is part of the problem. Maybe contact the makers of the fenders with a description and pictures.

unterhausen

Are smooth honjos anodized? I think I would take one of the chemical polishing compounds to an inconspicuous spot and see if it gets rid of it.

Iride01 

Kids or grandkids loose in the basement? Sometimes when I was one of those and left unattended I liked to spray whatever I could find that was nearby on things and think I was making them shine or at least making them better.

Grandparents, aunts and uncles probably wondered what was all over the stuff I made look pretty too.

Darth Lefty 

Fender mites.

samkl 

I don’t believe they are anodized. I tried polishing it out with a dremel and it didn’t work.

Also, this is a locked personal basement storage unit, no kids running around…

CliffordK

Hmmm.... any chance you got some road salt?

samkl 

Well, this only started in the summer so I doubt it…

So far my best guess is Framesaver, but I’d be surprised if that has a corrosive effect on aluminum.

Could it be radon or ozone or something else gross found in apartment basements?

EDIT: Or Gatorade???

andrewclaus

Do you by any chance store any bases or acids in there? Chorine bleach, muriatic acid, industrial pure vinegar, car batteries?

unterhausen

It appears to be products of corrosion. So sugar might do it.

tyrion

Sweat from head and butt? That would explain the location of the corrosion.

Koyote

I've got some hammered Honjo fenders on a bike, but I'd guess they have the same finish...And I sweat like crazy in this heat and am not too careful with my sugary energy drinks, and have not seen etchings like the OP's on my fenders. I have got a couple small patches of sort of pale white-ish blemishes, which is very different -- but also has me baffled.

While they are pretty fenders, they are also pretty effective, and they still work just as well to keep me and the bike clean when riding in lousy conditions.

JohnDThompson 

Looks like superficial corrosion of some sort. That's one reason I prefer hammered/textured mudguards over smooth, polished ones: the textured surface hides stuff like that.

Sy Reene

What chain lube and how wet do you leave your chain when lubing?

samkl 

I’ve used Finish Line and Prolink, and I try to wipe off the excess. But that’s an interesting theory, hmm.

thumpism 

Proximity to pool chemicals will do that.

thook

zombie flies reproducing on your fenders overnight?

djb

this was my thought also. Last year I worked on a friends bike that had bad corrosion in places and it was from being kept in a shed with pool chemicals. Bike hardly ever used so it was clearly from the pool chemicals.

is your garage very humid also? Our garage can be humid and I've seen similar ish corrosion on things that sit there for a long time like a car hydraulic jack etc that is steel.
humidity compounded by in winter a car regularly dripping off lots of salty snow and slush, combined with poor ventilation.

re sweat, chain oil etc, it's not localized corrosion, and seems evenly spread around, which supports a general air thing gong on. Ive seen this also on other stuff in our garage too.

A drag for you though.

djb

Oh, re excess frame saver. Ive only applied this to one frame, with little excess coming out afterwards, short term and long term, including riding the bike for months in very hot counties, but even then it seems to me that this product would actively stop any corrosion, not cause it....