T&T: Replacing alum rivets: Brass or Stainless?

[Mark Andrew]

Greetings all,

Just read Steve D'Antonio's newsletter article on stainless
hardware...probably the best and coherent explanation I've ever read on the
subject of stainless fasteners.

Well, I still have a question of priorities when choosing fasteners: On my
steel trawler, built in the mid '50s, I've got an aluminum pilot house
riveted to its aluminum structure.  The rivet heads were all covered by
bondo for appearance, but someone had filed down some of the rivet heads so
much, in places not much was holding the plate to the structure.  So we
removed most of the rivets, and replaced them with brass round-head machine
bolts.  Then I thought there may be a galvanic problem with the brass vs
aluminum, so we switched out all the brass bolts with 18-8 stainless bolts.
These will again be covered by bondo to provide a smooth surface to the
pilot house exterior.

Steve mentions that stainless, when embedded in a hydroscopic (I think he
meant hygroscopic) substance, can still corrode.  My question is: Would
bondo be that sort of substance?  Are our 18-8 bolts fine embedded in bondo
fastening aluminum together?  I'd hate to find out down the road that the
pilot house skin is not connected to the framework anymore.

And, would the brass bolts have been a better choice for this application
replacing the aluminum rivets?

Any ideas?

Mark Andrew
Holland, MI
"Black River", 56' steel, circa 1955