Technical Guides: “I live by the sea. What is the best material for external door handles? How can I prevent salt-spray marine corrosion?"

Approximately 3 million people in the UK (out of 60 million) live on the coast. For them, marine corrosion on coastal ironmongery is a daily battle, most commonly manifested in the form of rust. So, what is marine corrosion? Sometimes known as sea corrosion, or salt spray corrosion. Marine corrosion is defined as the accelerated deterioration of metal and other materials, caused by a reaction with the salt-heavy atmosphere of a coastal environment.

Salt-spray and atmospheric salt-content of coastal areas is incredibly destructive to many metals and other materials. While salt-spray is at its most destructive on the seafront, atmospheric salt spray corrosion can occur several miles from the sea due to wind spread and other factors.

Research has shown that corrosion of exposed steel on the coast can be 400 - 500 times greater than the same steel placed in the desert. Whilst marine corrosion is effective up to several miles from the sea, the destructiveness of salt spray is exponentially greater nearer the ocean. One study found that steel samples located 24 metres (80 feet) from the coastline corroded 12 times faster than those 243 metres (800 feet) from shore. To help explain how much of a cost marine corrosion extolls on people who live and work by the sea, the National Association of Corrosion Engineers has estimated the repair, maintenance, and replacement cost of marine corrosion worldwide at between $50-80 billion a year.

As architectural ironmongers, at More Handles we are often asked about how to prevent marine corrosion, rust, and atmospheric pitting in coastal door handles and other door furniture. By their nature, door handles, door knobs, pull handles and push plates, bell pushes and letter plates must be used on the exterior of a house or other building. In seaside towns and cities, marine corrosion can take a terrible toll on these products. So, how to battle this form of corrosion? And how can you carry out marine door maintenance? As with many things, prevention is better than a cure. When a customer asked what steps they can take to avoid salt-spray corrosion, we would tell them to choose their door furniture based on what materials are resistant to sea corrosion.

Lets take a look at some basic rules to remember when choosing corrosion resistant door hardware and coastal door handles for use outside by the sea.

1) Avoid lacquered Brass. Lacquer is a thin varnish coating applied to solid brass, ostensibly to prevent the brass from dulling down due to oxidization. The problem is, when used externally (especially by the sea) the lacquer coating is attacked at an incredible rate by atmospheric particles. When a lacquer breaks down, the first signs are black pitting marks and small black spots. These will eventually spread all over the item, and look very unsightly. We have seen even the best quality lacquers available deteriorate in a matter of months when used by the sea. What is the solution? Use brass that is not lacquered. Unlacquered brass will dull down faster by the sea, but the effect will be an antique one, rather than unsightly black pit marks. At More Handles, we carry a huge range of unlacquered brass ironmongery in different styles.

2) Ensure that your ironmongery uses a Solid Brass base metal. When purchasing Polished Chrome, Satin Chrome, and Satin nickel door furniture, remember that the base metal below these plated finishes makes a big difference in how long they will last when used outside. Manufacturers plate these finishes onto two base metals – Zamak and Solid Brass. Zamak should never be used externally, and if used by the sea, the nice new plating will pit and crumble off in a matter of weeks. Solid Brass is a very stable base metal to use, but remember, when using plated finishes by the sea, there is always a risk the finish may corrode due to the destructive particles. Generally, it is accepted that Polished Chrome finish plated onto Solid Brass from a reputable manufacturer is the most durable of all plated finishes.

3) Remember that Stainless Steel is not always ‘Stainless’. Stainless Steel is available in several different grades. It should be noted that none of them are rust-free, they are only rust-resistant in varying degrees. The most common grades of stainless steel used in architectural ironmongery are Grade 201, Grade 304, and Grade 316. Grade 201 and 304 should never be used externally, as they will certainly rust. Grade 316 can be used outside in most situations, however when used in a coastal environment, surface rust may occur.

4) When using Black ironmongery, be careful not to scratch or knock the paint. Black Ironmongery is generally powder-coated, which is basically a painted finish. This can be used in a coastal environment, but be aware that the material beneath the coating is usually cast iron or wrought iron, and sometimes steel. These materials are extremely susceptible to rust. It is vital that when fitting these items, care is taken not to chip the powder coated paint finish, especially on the screw heads, as this will result in rust streaks and corrosion. If chips do occur, they should be touched in with black paint.

5) Consider materials that don’t have a plated finish, such as Solid Brass, Solid Bronze, and Solid Pewter door furniture.

These three materials are the most impervious to decay in an exterior and coastal environment. While they will accrue deposits from salt-spray, they will not corrode in a destructive or aesthetic way, and can all be cleaned up quite easily. As these are not plated finishes, there is no plating to corrode and so the products are far more stable for exterior use, even in coastal environments.

Let’s take a look at some of the most common finishes available for architectural ironmongery, and assess whether they are suitable for exterior coastal use.

Solid Brass: YES if unlacquered, NO if Lacquered.

Polished Chrome: YES if used on a solid brass base metal, NO if used on a zamak base metal.

Satin Chrome: YES if used on a solid brass base metal, NO if used on a zamak base metal.

Satin Nickel: YES if used on a solid brass base metal, NO if used on a zamak base metal.

Antique Brass: YES if the finish is created by oxidization, NO if it is a plated finish.

Black Ironmongery: YES but with care and maintenance

Porcelain and Ceramic: YES.

Aluminium: NO.

Wood and Timber: YES but with care and maintenance.

Stainless Steel: Grade 316 only, may corrode by the sea.

Solid Pewter: YES

Plain Cast Iron: NO

Glass: YES, but be aware of the base metal of the rose or backplate.

So, yes, living by the sea can present some challenges when it comes to fitting external ironmongery- but at least you get to live by the sea!

If you're looking for coastal door handles please see our Blu Performance collection for corrosion resistant door hardware.

Call one of our architectural ironmongery specialists to discuss anything in more detail - we will try not to sound too jealous!

TEL - 01228 516516

EMAIL - sales@morehandles.co.uk