C3 Rivet Bumps

[Patrick B.]

Re: C3 Rivet Bumps

Ken, Terry and Joe:
There is another reason why some cars are more susceptable to rivet bumps than others. A friend of mine who is a professional restorer has noticed that there is an appreciable variation in the thickness of the bonding material used to bond the headlamp bar bonding strip to the surround panel. Cars with a thicker layer of adhesive tend to have more room for corrosion products to build up on the rivet before bumps develop. I don't know if some cars are completely immune or whether the onset is simply delayed given a particular climate. Kind of like the luck of having "good genes."

[Kenneth B.]

Re: C3 Rivet Bumps

Ken, Terry and Joe:
There is another reason why some cars are more susceptable to rivet bumps than others. A friend of mine who is a professional restorer has noticed that there is an appreciable variation in the thickness of the bonding material used to bond the headlamp bar bonding strip to the surround panel. Cars with a thicker layer of adhesive tend to have more room for corrosion products to build up on the rivet before bumps develop. I don't know if some cars are completely immune or whether the onset is simply delayed given a particular climate. Kind of like the luck of having "good genes."

THANKS
That is kind of what I thought. I wondered if some how the heads got covered on some cars & not others that would protect the aluminum from corroding or as you say leave room for the expansion of rivit heads
KEN

[Joe L.]

Re: C3 Rivet Bumps

I believe salt air/mist can do it too, as can any moisture. Coastal areas or places with high humidity would lead to this problem, but Joe is well inland. The same can not be said for all of California.

The principal corrosion source is galvanic action between the aluminum rivet and the steel support. All that is required is the presence of moisture, as in high humidity and rapid temperature changes, to create a primitive battery between these dissimilar metals. I can't get into the chemistry of this action, but I know materials that are far apart on the Periodic Table are prone to this phenomenon. The rest I will leave to those with a chemical dependency. I know there are several Chemistry PhDs on here, and they can go into it further if anyone is interested.

Terry------

Yes, if one goes to the extreme coastal areas of California, one will definitely see a whole bunch of cars with "body rot" akin to that which one sees on a widespread basis in the east and midwest. When I go to Santa Cruz or Half Moon Bay I often see this. In other parts of California, I rarely see any cars with even the slightest signs of "body rot".

As far as elements being far apart of the periodic table and resulting in galvanic corrosion, it's not the periodic table-----it's the electronegativity series. The further apart that metals are on the electronegativity series, the greater the tendency to galvanic corrosion.

[Terry M.]

Re: C3 Rivet Bumps

Terry------

As far as elements being far apart of the periodic table and resulting in galvanic corrosion, it's not the periodic table-----it's the electronegativity series. The further apart that metals are on the electronegativity series, the greater the tendency to galvanic corrosion.

I should wash my hands of this Chemistry stuff. I took Physics. I know who some of the Chemical PhDs are and I should have consulted them first, but then I never would have got the post up.