Originally Posted by nickcrowhurst
Don, to prevent electrolytic corrosion you need to electrically isolate the dissimilar metals. One way is to use non-metallic washers under the head and the nut. I have used Tufnol. A perfect job also sleeves the hidden part of the bolt in plastic tube. A compromise, which we use when fixing stainless steel fittings to aluminium masts on yachts, is to bed the bolt heads and washers in a layer of zinc chromate paste. This thick yellow paste is available from specialist yacht spar stores, but a pharmacist would probably supply it. It acts as an insulator between the dissimilar metals. Nick.
I've looked all over for zinc chromate paste. It's hard to find since the movie "Erin Brockovich", all about hexavalent chromium (Cr++++++).
I think one function of the zinc chromate (and the now popular zinc molybdate) is that the zinc oxidizes preferentially to the aluminum, since it is more anodic than either aluminum or steel. That's why I wanted to try it.
The isolating bushings are equally scarce here in the midwest, away from the coast and salt air. Not many sail lofts or chandlers.
Again, thanks for the help.