Is there any harm done when brake pads/blocks get mashed up in the wet?

[Tojo]

It WAS!

This is what 5 previously WHITE baby wipes looked like after cleaning the rims another time when braking had started to get a bit iffy on a wet ride.

View attachment 339728

Rim brakes always take a bit longer to bite in the wet. I'm not talking about 'iffy' like that - I am experienced enough to apply the brakes a few seconds before I need to in the rain to get the water off the rims. What I am talking about is so little friction that the brakes barely work. Like braking on old stainless steel rims used to be in the rain.

Were those wipes a chocolate colour before.....

 

[Tojo]

Yes, we know the aluminium powder is from the rim. But wear rate is a function of braking distance in the wet, not traveling distance.

When aluminium oxidises it deposits a black powdery substance which is caused by dissimilar substances, which could be dissimilar metals or contamination
( usually salts ) and is grouped in metallurgy inspection as erosion corrosion.