Toe rail corrosion

[Guest]

The aluminium toe rail which is fastened with SS bolts is suffering from pitting corrosion. It is not connected to the electrical circuit or earth. When I put a voltmeter between the rail and a earth it registers up to two volts when wet with spray and about 0.5 volt when dry. Disconecting the battery seems to make no difference. Any ideas. regards wayne

 

[Guest]

You have a classic case of Galvanic corrosion, cause by the dissimilar metals, ie St/Stl and Ally. The Spray is acting as the electrolyte and forming a cell, much as it would if under the water.

You need to electrical isolate the bolts and the toe rail by ensuring that the bolts do not touch anywhere. This can be done by putting a nylon washer under the head of the bolt and that the clearance through the ally is bigger. An added precaution is to coat the bolt and around the hole with a varnish which is allowed to dry before re-assembly.

If the hole into the toe rail is threaded, then this is much more difficult. PTFE pipe jointing tape wrapped round the bolt thread sometimes is effective. If the ally toe rail was never anodised, ie with a protective film, then it will corroded anyway. Varnishing the efected area will helps additionally. I hope this helps.