So you bought your own shipping container and are using it for storage. One of your first questions now that you are the proud owner of a Conex container is “What do I need to do to take care of and maintain my shipping container?”

The good news is that by their very design, shipping containers are constructed out of heavy gauge steel and built to be durable for many years, with minimal maintenance.

How long do shipping containers last?

You can expect to get a minimum of 15-20 years of use from your shipping container. When a Conex container is retired from international cargo shipping service they are resold as wind and water tight units into the storage market or to be repurposed for other uses.

With some basic preventative maintenance and planning, your sea container can easily serve you with a further fifteen or more years of use.

Annual inspection of your storage container

Mark your calendar to make an annual inspection of your storage container. Check for any indications of structural rust, especially in the frame parts of the box where water may have collected for any period of time. Inspect the rubber door seals to check for deterioration. Old seals eventually become brittle and won’t maintain a water tight seal. As with anything – if you address any wwt shipping containers problems early on and perform a minimum level of maintenance – you can save time and money on repairs later. Your local climate will be a factor in what kind of maintenance that you have to perform and the rate at which your container will deteriorate. Anyone who has owned a car in a wet, temperate climate will know that the moisture, snow, and freezing temperatures cause a more rapid deterioration of metal compared to a warm, dry environment (like Arizona for instance).

Preventative Maintenance is key 

To help maximize the lifetime of your cargo container storage, we will share a few tips to help maintain your container:

Protect against the effects of water and excess moisture

Container condensation or “container rain” is a pretty common thing to monitor during your periodic container inspections. While your sea container is designed to be water tight and prevent moisture from entering from the outside, there is moisture in the air and even contained within the items that you may be storing.

“Container rain” is the condensation of the moisture in the air that occurs inside the closed metal structures. An excessive accumulation of condensation can cause serious damage to some types of items (example electronics or paper documents) and can also accelerate the oxidation process (appearance of rust we will discuss later).

How does condensation occur inside shipping containers?

The metal walls of shipping containers tend to conduct heat very well. As the air temperature drops outside from day to night time, the steel surfaces of the container walls rapidly cool. Once cooled low enough, the metal surfaces will reach what we know as the ‘dew point’ – the temperature where airborne water vapor condenses back into a liquid again.

When warm, humid air comes into contact with the cool metal container walls, the moisture condenses from a vapor to its liquid state, causing water droplets to from on metal surfaces – most of the condensation collects on the ceiling. In regions of the country where there is a great difference between daytime and nighttime temperatures, the risk of container rain damaging your stored items is greater.

How can we deal with moisture condensation in shipping containers?

There are three main factors to consider to minimize the problem of moisture condensation in your storage container.

1) Reduce the amount of humidity in the conex container

Inspect the container ceilings and walls for visible moisture condensation. Prior to loading the container, examine the interior surfaces to ensure that there is no pooled water and dry any water that may have collected.

Insulation. Insulating the walls of your container can reduce the temperature of the walls dropping to dew point, and therefore eliminating condensation from occurring.

Check out our Guide How To Insulate A Shipping Container 

Installing a Vapor Barrier

A vapor barrier can help reduce excess moisture condensation on the container walls. A vapor barrier is any material used for damp proofing. Commonly a plastic sheet, that prevents diffusion of moisture through the walls, doors or ceiling.

Dehumidifiers and air-con units. If you are intending on storing items that are sensitive to the effects of moisture, you may need to consider using more direct solution to cooling and removing humid air. Air conditioners and / or dehumidifier units are effective at maintaining stable, dry conditions for storage containers in problem climates or seasons of the year.

For a less costly and lower maintenance method of managing humidity inside the container, you could employ desiccants inside. Desiccants are “hygroscopic substances” which absorb atmospheric moisture.

Think of those “Do Not eat” silica gel packets that are usually found inside bottles of food supplements or product packaging. Desiccants are available in a number of forms – most commonly contained in strips hung on the walls or suspended from the ceiling or bags on the floor of the container. The desiccant bags should be replaced every 10 to 12 weeks – depending on the time of year and your local weather conditions.

2) Ventilate to allow warm humid air to escape

Ventilation. Consider your environment. If your container will be stored in a climate where there is a significant day/night temperature fluctuation, you may need to employ greater measures to mitigate “container rain”.

Containers are often renovated and fitted with vents to allow air circulation and avoid the build-up of heated air inside the container. This simple step can go a long way to eliminating the effects of condensation.

3) Store dry goods to avoid condensation.

Make sure you only store 100% dry goods in the storage box. Be aware that some materials, such as fresh wood, can have an intrinsically high moisture content. This means that moisture from the items themselves can release moisture into the air and can cause humidity levels to rise inside the container.
Avoid placing moisture sensitive objects (like furniture or cardboard boxes) directly in contact with the walls where water droplets are most likely to condense and collect. Be aware that some items (ex. electronics or dried food stuffs or cardboard boxes of paper documents which are susceptible to mold) may be at risk of the effects of moisture build up and plan accordingly.

Rust: How to prevent & avoid shipping container rust

Even though Conex containers are designed to be watertight and be used in all weather conditions, they are ultimately made of steel and thus susceptible to the problem of rust.

The good news is that most shipping containers are manufactured out of corrosion resistant Cor-Ten steel and we can take measures to protect against the onset of rust and slow its corrosive effects. If you purchased an “as is” container, it is quite likely that a used shipping container has had a lot of exposure to salt water and salt air which all accelerate corrosion. A 1-trip or new container will not have that degree of corrosion.

What causes shipping containers to rust?

Rust occurs when iron reacts with oxygen in the air, or chloride in water. Marine grade steel has anti-corrosive properties, but because of the harsh, maritime environments that containers are exposed to, rust will eventually, occur.

When a shipping container is exposed to both oxygen and water – an oxidation chemical reaction occurs. The reaction between the steel, the water, and oxygen creates hydrated iron (III) oxide, which we can experience as rust. Shipping containers can also start to rust if their metal surface sustains any damage during transit. When the container is impacted during loading, the protective coating on the outside of the container may be damaged and bare metal exposed, which creates a foothold for the oxidation reaction to get started.

Two different types of shipping container rust

The most obvious rust on the exterior walls of a container would be considered “non-structural” rust as it occurs on the surface of the walls. Surface rust is unsightly, can rub off on and discolor items that come into contact, and will negatively affect the resale value of a container. A visibly rusty container may not pose any danger to its users, but few people want to see (or buy) a rusty steel box.

The second (and more insidious) type of container rust is known as “structural rust”.

This more advanced state of corrosion, which has begun to negatively affect the structural integrity of the container). Significant structural rust can render a container unusable for many purposes due to structural instability.

Significant structural rust may prevent the owner from getting the container CSC certified. According to portshippingcontainers.com :

“CSC means ‘Container Safe Convention’ the container is safe for use and is capable of withstanding the sometimes heavy stresses of shipping cargo cross-country and overseas…need to be inspected and certified according to international regulations.”

How to treat early signs of rust

Catch small surface rust issues early on when they first appear. If you catch them early enough, the rusted area is easily treated and cleaned away. Spot and repair scrapes, dents, and scratches, should be dealt with before they show signs of rust, to prevent further corrosion damage that could worsen the issue from a non-structural problem to a structural problem.

The initial signs of rust should be removed. First prepare the problem area by using a wire brush or sand paper to sand down any visible rusted surfaces.

To properly remove the rust, you need to sand right down to bare metal where you can no longer see any signs of rust. After the surface rust has been completely removed, wipe the bare area with vinegar and allow to dry. Once the vinegar has dried, you may apply a layer of rust inhibiting primer or use marine grade DTM (direct to metal) paint to cover the area. If the surface rust problem is more advanced, the remedy is to completely sand blast the exterior container walls and seal and freshly paint the container. For most storage uses, the expensive process sandblasting and completely refurbishing the container is not required.

How do I prepare my container for painting over rust?

As a rough guideline – to repaint a 20-foot container you will require four gallons of paint, and need eight gallons to cover a 40-foot container.

Prepare your container for primer and/or paint application by first sanding down any visible rust patches. A pressure washer is ideal for washing off any layers of dirt and dust. Sand rust patches down with a wire wheel or sandpaper.

It’s a good idea to apply a rust inhibiting primer coat over the area first to ensure the top coat of paint adheres to the metal.

Get the advice of your local paint vendor to determine which primer they stock will be best for outdoors metal surfaces.

Allow enough time for the primer coat to completely dry before applying the final, top coat of paint.

What kind of paint should I use for rust proofing my shipping container?

There are a number of options that you can find to suit your needs, paint availability and budget.

Choosing the correct paint for your shipping container

The type of paint you decide on for your container will depend on how you intend to use it.

1) A water based paint (that is better for the environment with lower VOC levels). With proper preparation and application, water based paints can be equal or better at inhibiting rust – compared to the traditional oil-based paints.

2) Industrial grade alkyd enamel paints are reasonably inexpensive and easy for non-professionals to work with.

You can expect your alkyd enamel finish to last between five to ten years.

3} Polyurethane paint is a heavy duty paint seen in industrial use. It’s important to be aware that the chemicals in the paint can be more hazardous to use. Since there specific procedures for the mixing and application of polyurethane paint, you may wish to seek the services of a professional to apply this type of paint.

4) Zinc paint. Using an application of zinc-based paint will slow the onset of shipping container rust effectively. By a process know as ‘cathodic protection’ – the zinc in the paint slows the rate of rusting of the underlying steel.

Sandblasting the entire exterior of the container is not recommended for most cases. Sandblasting an entire container is a costly process as you need to engage a professional who has the equipment and the sandblasting will completely remove a lot of great protection provided by the original high quality marine grade paint. Since a home paint job is not going to offer the same level of rust protection as the original paint, the wise course of action is to prime and paint over the original marine paint.

Position the container on a level foundation

The easiest step you can take to protect against the effects of water and rust is to position your shipping container on level ground – as opposed to a low lying depression where rain water will collect.
If puddles of water accumulate under or around the container, the conditions are there for rust to rapidly develop. If your container is set directly on the ground, the bottom is in contact with ground moisture and more likely to rust.

First, select a location that is on raised and level ground. Builders recommend setting your Conex container up on a basic foundation using a simple foundation of concrete blocks or railroad ties – which will also have the added benefit of improving air circulation under the container..

A common problem area to look out for is the bottom of the container doors as water tends to collect in that area.

Maintain container door hinges and gaskets

While shipping containers are simple structures with few moving parts, we do need to perform some maintenance on the doors.

The easiest and most obvious is to lubricate the container door hinges. Metal hinges can seize up after a long period of disuse. Applying an all purpose lubricant like WD40 or 3in1 oil when you do a container check, will keep the hinges from rusting and getting bound up and doors working smoothly.

Replace worn rubber seals on doors.

Shipping containers are engineered to be a watertight sealed environment and the metal doors utilize rubber gasket type of seals.

The rubber generally have a life span of close to 10 years before cracking, degrading and losing their ability to rightly seal the door against moisture. In the case of badly degraded seals, you can replace them with a container door gasket kit available online.

By paying attention to these tips, you can ensure your shipping container storage unit protects your items for many years.