Is Zinc Waterproof?

No, Zinc is not waterproof but it can be used to help protect other metals from high levels of corrosion when exposed to water.

Rather than being used in its pure form, zinc is most often used to form metal casting alloys.

This is because zinc corrodes at a slower rate than many other metals.

What Happens When Zinc is Exposed to Water?

Zinc is not waterproof and slowly corrodes when it is exposed to water or air.

The corrosion rate of zinc is low in neutral pH but increases when the pH of the water is acidic or alkaline.

It is difficult to predict the corrosion rate as it depends on the water the zinc is exposed to.

Zinc is more corrosion resistant than iron or steel which is why it is commonly used as a galvanized coating for these materials.

Zincs Reaction to Various Water Types

The type of water zinc comes into contact with will impact how quickly it corrodes. Here is a rough guide to help you decide if zinc is the best material for your uses:

De-ionized Water

Also known as distilled water or pure water. This is very corrosive to zinc coatings. The dissolved oxygen and carbon dioxide increase the corrosion rate.

Fresh Water

The corrosion of zinc in freshwater depends largely on the impurities of the water. Different substances in the water will impact the pH level as well as the temperature of the water.

A general data-supported trend is that soft water is considerably more corrosive than hard water.

If the zinc is going to be exposed to freshwater, these are the factors that will impact the overall corrosiveness of the water:

Gasses: an increased level of oxygen will increase the corrosion rate. A fully immersed item is better than a partially immersed item as there is less oxygen in the water. Springs have high oxygen levels so have higher rates of corrosion while wells have low oxygen rates so have lower levels of corrosion.
Flow Rate: water with a higher flow rate is likely to cause more corrosion due to the increase in abrasion experienced.
Water Hardness: In soft water there is less carbonate so the water is more corrosive. In hard water the zinc combines with carbonates and forms zinc carbonate which creates a film that actually slows corrosion.

Seawater

Similar to freshwater, there are a number of factors that impact how quickly zinc will corrode in saltwater. The main factors are:

Ion Interaction – zinc can interact with other materials such as calcium and magnesium to form passive compounds. These compounds form on the surface and slow the corrosion. In warmer water zinc struggles to develop these compounds so corrosion is not slowed.
Temperature: Tropical seawater is more corrosive than colder waters as reactions between zinc and oxygen happen quicker at higher temperatures.

Tidal zones and wash zones are one of the most corrosive areas as the movement increases the corrosion rate.

Zinc Protects Other Metals

Sometimes people think zinc is waterproof as it is used to protect other metals.

However, this is not the case.

The Zinc coating is sacrificial and will wear away over time.

Rather than the water simply washing over the zinc without having an effect as it would if it were waterproof, the zinc starts to slowly corrode.

As it is sacrificial, this means that the zinc defers to the metal it is protecting, significantly reducing the development of corrosion of the other metal.

The steel or iron will not corrode as the zinc will corrode first, even if there is a scratch that exposes the metal it won’t be impacted while there is still a zinc coating around it.

This is because the zinc is actively protecting the metal.

Although the zinc is not waterproof you can think of it as “taking one for the team” as it protects the metal and the zinc itself corrodes (just at a slower rate).

How Can A Zinc Barrier Stop corrosion?

According to Sharretts Plating, Zinc can corrode up to 100 times slower than other metals (depending on environmental conditions).

A zinc coating is used as a barrier that stops moisture from getting onto iron or steel surfaces. Iron and steel are both highly susceptible to oxidation so will rust when exposed to moisture.

Common Uses of Zinc

Zinc is a natural element that is commonly used to protect steel and iron from rusting through zinc galvanizing processes.

The second most common use of zinc is creating brass by alloying zinc with copper.

Zinc plating is common and this is where the zinc is electroplated onto an iron-containing metal. This creates a barrier that is resistant to corrosion.

This is known as zinc plating and is a low-cost, popular way to protect certain surfaces.

IMPORTANT: Zinc plating is not recommended for outdoor use as although it is inexpensive it corrodes easily compared to other methods.

For example, zinc-nickel plating is more corrosion-resistant and lasts longer in water. This is because the nickel helps slow down corrosion.

More durable options include hot-dip galvanized steel which involves zinc but using heat rather than an electrical current.

Zinc Vs Zinc Alloy Plating

It’s common for zinc to be alloyed with other metals, usually nickel or tin.

This helps to increase the corrosion protection as zinc-nickel alloy offers protection 10 times greater than zinc alone.

The downside to using zinc plating is that it doesn’t handle exposure to acids or alkalis well. It also isn’t good for marine applications as seawater impacts the materials durability.

If you’re looking for a metal that can hold up in wet environments take a look at galvanized steel.

Unlike zinc plating, galvanized steel can be used in marine environments as it has a protective layer preventing the iron in the carbon steel from rusting.

Hot dip galvanizing is the best method for protecting items that will be submerged in water as it provides complete coverage.