Container shims: uses, modifications and possible fit-outs

The container shim: a discreet but strategic accessory

When installing a shipping container, whether new or used, the first question is how to support it. A standard 20-foot container weighs around 2.2 tonnes empty, a 40-foot around 3.8 tonnes. Once loaded, we are talking about several dozen tonnes. Even on ground that looks flat, a container always ends up working: one corner sinks slightly, the floor deforms, moisture rises by capillary action. This is where the container shim comes in.

This recycled polypropylene accessory, measuring 40 x 26 x 4.5 cm and weighing 6.2 kg, has an apparently modest function: distributing loads and compensating for ground irregularities. But its role is in fact decisive for the safety, longevity and modularity of an installation. Whether you are a logistics professional, site manager, event organiser, farmer or individual, the shim determines how you will be able to use your container.

In this article, we will explore in depth the uses of the container shim, the modifications it facilitates and the fit-outs it makes possible. We will see how a €14 accessory can change the game on a construction site, on a farm or in a garden.

Why shim a container? The technical issues

Distributing loads and preventing deformation

A shipping container is designed to rest on its four reinforced corners, called corner castings. These metal parts are sized to bear the entire weight of the container and its contents, whether during lifting, stacking or placing on the ground. When a container is placed directly on hard ground, the corners transmit very high pressures to the ground. On concrete or asphalt, this is generally not a problem. On soft ground, however, the corners can sink, creating stress points that eventually deform the structure.

The container shim increases the bearing surface under each corner. By distributing the load over 40 x 26 cm instead of a point surface, it reduces ground pressure and limits the risk of sinking. This is particularly important on compacted gravel, earth or sand, where bearing capacity is uneven.

Creating an air gap and fighting humidity

A container placed directly on the ground is in direct contact with moisture. The marine plywood floor, even when treated, eventually absorbs water by capillary action. The metal rails rust, the wood swells, musty smells appear. By raising the container by 4.5 cm, the shim creates an air gap that allows both ventilation and water drainage. This is crucial for outdoor installations, especially in humid or coastal regions.

Compensating for uneven ground and stabilising the whole

Perfectly flat ground is rare. A slight slope, a sunken area, a stony surface: all situations where a container placed directly on the ground will tip or work. The shim allows you to compensate for a difference in level by stacking up to five units. This stacking capacity offers a valuable adjustment margin, while maintaining good stability thanks to the interlocking shape of the shims.

Uses of the container shim by sector

In logistics and transport

Logistics professionals use shims to stabilise containers awaiting loading or unloading. On a storage platform, a container placed on shims is easier to move later: a forklift can be slid under the corners without risking damage to the floor. Shims are also used during shifting, i.e. the lateral movement of a container, to maintain a stable position before final placement.

It should be remembered, however, that shims do not replace regulatory securing devices. In road transport, a container must be fixed to the chassis with twist-locks. In maritime transport, securing is provided by standardised systems. Shims are used as a complement, for temporary storage or stabilisation on the ground.

In construction and on building sites

On a building site, containers serve as welfare units, offices, changing rooms or storage areas. They are often installed at the start of the project, on land that has not yet been prepared. Shims allow them to be placed quickly on earth or gravel, compensating for irregularities. Their light weight (6.2 kg) is an asset: one person can move and reposition them as work progresses, without the need for lifting equipment.

Another advantage: polypropylene shims resist impacts and bad weather. On a building site, they do not rot, do not break and are not sensitive to common chemicals. They can be cleaned with a water jet or pressure washer (up to 200 bar and 80 °C), which is appreciated after a muddy winter.

In the events industry

The events industry increasingly uses containers as dressing rooms, pop-up bars, storage spaces or stands. These installations are temporary by nature and must be set up quickly on various surfaces: grass, gravel, asphalt, sand. Shims allow a container to be placed in minutes, without earthworks. They ensure public safety by preventing any tipping, and facilitate dismantling at the end of the event.

In agriculture and rural areas

Farms use containers to store grain, tools, equipment or plant protection products. The ground in storage areas is often packed earth or gravel, and humidity is a recurring problem. Shims prevent the floor from being in direct contact with damp ground, which limits corrosion of metal parts and degradation of the plywood. They are also useful for shimming a container on sloping ground, common in rural areas.

For individuals and self-builders

More and more individuals are installing a container on their land to make a workshop, storage room, garden office or even a light dwelling. Shims are an economical alternative to concrete slabs, provided the permissible loads are respected and a sufficient number of support points are provided. They allow you to test the layout before committing to heavier work, and to move the container if necessary.

Modifications and fit-outs made possible by shims

Raising the container for interior fit-out

When converting a container into living space or a technical room, the question of floor insulation quickly arises. A container placed directly on the ground transmits cold and humidity. By raising it on shims, you create a ventilated crawl space. You can then consider installing an insulated floor, networks (water, electricity) running under the container, or simply easier access for maintenance.

The 4.5 cm height may seem modest, but it is enough to create air circulation. For greater raising, up to five shims can be stacked, giving about 22 cm of lift. Beyond three shims, it is advisable to check the stability of the whole and the flatness of the ground.

Creating a terrace or level access

A container raised on shims can be integrated into an outdoor layout: wooden terrace, steps, access ramp. The raising allows the container floor to be aligned with an existing terrace or access path, which facilitates movement and improves accessibility for people with reduced mobility. This is important if the container is used as an office, retail space or reception area.

Facilitating the installation of networks and technical ducts

In a container fitted out as a workshop or technical room, shims free up space under the floor that can accommodate ventilation ducts, electrical cables, water pipes or drains. This avoids drilling through the floor or running networks inside, which simplifies fit-out and maintenance. This configuration is particularly interesting for semi-permanent installations, where you want to be able to modify networks without demolishing everything.

Allowing the container to be moved and repositioned

A container placed on shims is easier to move than one placed directly on the ground or on a concrete slab. A forklift or jack can be slid under the corners, the shims removed, and the whole moved. This modularity is valuable for professionals who need to reorganise their storage space, or for individuals who want to test different layouts before settling.

How to use a container shim correctly

The number of shims needed

For a standard container, one shim per corner is generally recommended, i.e. four shims. On soft ground or if the container is heavily loaded, shims can be added under the longitudinal rails at regular intervals to prevent the floor from flexing. In this case, it is essential that all shims are at the same height to avoid creating stress points.

Step-by-step installation

1. Check the bearing capacity of the ground and identify irregular areas.
2. Slightly lift the container using a jack or forklift, observing safety rules (never work under a suspended load).
3. Slide the shim under the relevant support point, ensuring it is flat.
4. Repeat for each corner.
5. Check the stability of the whole: the container must not tip or rest unevenly.

On very uneven ground, up to five shims can be stacked to raise one corner. Beyond two or three shims, it is advisable to check the flatness and bearing capacity of the whole, and not to exceed the indicated load limits.

Precautions to take

• Do not use the shim as a lifting device: it is for stabilising, not lifting.
• Respect the maximum load of 5.5 tonnes on hard ground and the working load of 2.1 tonnes.
• On soft ground, reduce the load or increase the number of support points.
• Regularly check the condition of the shims: no cracks, crushing or deformation.
• Replace any shim showing a visible defect.
• Avoid strong solvents when cleaning; prefer water and a mild cleaner.

Comparison with other stabilisation solutions

Wooden shims

Traditionally used in maritime and road transport, wooden shims are inexpensive and easy to cut to size. But they degrade quickly on contact with moisture, can rot, split under heavy load and sometimes attract wood-boring insects. Their lifespan is limited and their load capacity varies greatly depending on the wood species and quality.

Recycled rubber shims

Rubber offers excellent grip, which is useful for shimming vehicle or trailer wheels. But it is generally more flexible and less suited to heavy, concentrated static loads such as those of a container. It can deform over time under permanent load.

Concrete blocks and foundation pads

For permanent installations, concrete blocks or reinforced concrete pads offer very high bearing capacity and great stability. But they are heavy, difficult to move and require ground preparation work. They are therefore reserved for permanent installations, where there is no need to reposition the container.

The polypropylene shim: a relevant compromise

The recycled polypropylene shim sits in between: more durable and stronger than wood, more rigid and stable than rubber, more mobile and lighter than concrete. It is particularly suitable for semi-permanent installations or frequent repositioning needs. Its price of €14 makes it affordable to equip a complete container without straining the budget.

Regulations and best practices

What the regulations say

A shipping container must comply with ISO 668 and ISO 1496 standards, which define dimensions, loads and tests. For a permanent installation, especially if the container is used as a dwelling or ancillary room, a planning permission may be required. Shims themselves are not subject to specific regulations, but their use must guarantee the safety of people and property.

In road transport, the Highway Code requires that the load be secured so that it does not move. Shims do not exempt you from this obligation: they are a complement, not a substitute for standardised securing devices (twist-locks, straps, chains).

Good safety practices

• Never work under a suspended container without reliable mechanical support.
• Check the stability of the whole before any intervention.
• Use a sufficient number of shims and position them under structural areas (corners, rails).
• Do not exceed the load limits indicated by the manufacturer.
• Visually inspect the shims before each use.

Maintenance and lifespan

Maintenance of a polypropylene container shim is minimal. Cleaning with a water jet or pressure washer (up to 200 bar and 80 °C) is enough to remove mud, residue or dirt. Polypropylene resists most common chemicals, but it is best to avoid strong solvents that could damage the surface.

For prolonged storage, it is recommended to store the shims away from direct sunlight to limit UV ageing, although the material is treated to withstand bad weather. Regular visual inspection is advisable: check for cracks, crushing or deformation that could reduce load capacity. If a shim shows a visible defect, it must be replaced.

Conclusion: a small accessory with a big role

The recycled polypropylene container shim is a simple accessory, but it plays a key role in the safety, longevity and modularity of an installation. It stabilises a container on any type of ground, raises it to fight humidity, compensates for uneven ground and facilitates interior and exterior fit-outs. Whether you are a professional or an individual, it helps you get the most out of your container, without undertaking heavy work.

At €14 per unit, it is a modest investment for a considerable gain in safety and comfort. Remember to plan for four for a standard container, and do not hesitate to add more if your ground is soft or your container is heavily loaded. And remember: the shim is a stabilisation accessory, not a lifting device. Respect the permissible loads and good safety practices, and your installation will last for years.