Can you make zinc anodes from car wheel weights?

Vyv Cox

Can zinc anodes be made using old melted down car tyre balance weights? Vyv Cox has the answer

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In an attempt to make some new zinc anodes for the boat, I melted down old car tyre balance weights.

They are made of zinc and are marked ZN. I cast them to make new zinc anodes – but they didn’t work.

What is likely to have gone wrong? Is the zinc from the tyre weights of the wrong quality?

Juha Ketosara

Vyv Cox responds:

Automotive wheel balance weights may be made from either zinc or lead alloys. Although the density of zinc is somewhat lower than lead, zinc weights are easier to install and remove from wheels and have therefore become more popular. The composition of the zinc alloy is not critical for wheel weights and can vary enormously, with zinc levels ranging between a little over 70% to 90%.

The remainder can be metals added to enhance the performance of the weight, such as strength or formability. Compositions are the manufacturer’s choice, as there are no standard specifications for these items. The composition provided by one manufacturer is:

  • Zinc 71.5-96%,
  • Aluminium 2-28%,
  • Copper 0-11.5%.
zinc anodes on a boat

If zinc anodes are denuded like this, they will need replacing. Credit: Katy Stickland

So you can see the composition can vary enormously. By comparison, the composition of zinc anodes is accurately controlled to meet the US MIL standard A-18001K:

  • Aluminium 0.10-0.5%,
  • Cadmium 0.025-0.07%,
  • Copper 0.005 max%,
  • Iron 0.005 max%,
  • Lead 0.006 max%,
  • Others Total 0.01 max%,
  • Zinc Remainder.

The percentage of zinc in this alloy is greater than 99%, so it is no surprise that you found anodes cast from wheel weights were not effective. It is known that even cleaning anodes with a steel wire brush can inhibit their protective properties, as can recovering used ones without taking precautions to eliminate the very low levels of iron in the donor product that reduce or cancel their effectiveness.

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