It's a Wrap: Wrapping the Cables

Previous posts in the New Narrows Bridge Series:

With the deck completed, there are still quite a few tasks to complete before the bridge is finished. The cables, comprised of over 19,000 miles of half-centimeter steel wire, joined end to end and woven back and forth as a single unit, have been spun and compacted, but remain unfinished.

To increase their resistance to corrosion, they are wrapped around their circumference with another layer of galvanized steel wire, leaving a smooth surface ready to be painted. The uncovered cables are first covered to minimize the risk of trapping moisture under the wire wrap,

An impressive rotating spinner tightly winds the steel around the cable like a monstrous black widow spider preparing her prey for dinner. The cable is first coated with a corrosion-inhibiting paste. For decades, cables were coated with red lead paste, which worked well, but has not been used since the mid-1990s, when the lead was recognized as an environmental hazard.

Bridge builders now use a urethane-zinc paste, about the consistency of mayonnaise. The idea is to apply it thickly, so that it oozes between the wrapping wires to form a solid anti-corrosion coating. The paste is manufactured in Italy, and 1,710 five-gallon buckets were required, each of which weighed 66 pounds.

The cable is wrapped in “bays” — 40-foot sections of cable between suspension bands, 270 in all. Each bay requires 3.3 miles of wrapping wire, a total of 948 miles. Three coats of rubberized paint then complete the finish, giving the cable a solid appearance.

Next: Opening Day!

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