Container shim – any ground type: uses, conversions and possible fit-outs

The container shim: a simple accessory for stable placement on any terrain

The container shim is a handling accessory that slides under the corners or bottom rails of a shipping container to compensate for ground irregularities, distribute the load and prevent the structure from resting directly on soft or uneven ground. This recycled polypropylene model, measuring 40 × 26 × 45 cm and weighing 6 kg, is designed to adapt to any ground type: compacted earth, gravel, compacted sand, concrete, asphalt or paving stones. Its maximum load on hard ground reaches 5.5 tonnes, with a working load of 2.1 tonnes and a safety factor of 1.5. Stackable up to 5 units, it withstands high-pressure cleaning (80 °C, 200 bar) and is sold individually at €38.

This article explores the many uses of this shim, the conversions it enables and the fit-outs it makes possible, for both individuals and professionals.

Why use a container shim?

Placing a shipping container directly on the ground is not without consequences. An empty 20-foot container weighs around 2.2 tonnes, a 40-foot around 3.8 tonnes. Once loaded, the weight can reach several tens of tonnes. The load is mainly distributed over the four standardized corner fittings according to ISO 668 and ISO 1496. Without shimming, these support points can sink into soft ground, cause deformation of the floor or bottom cross members and make doors difficult to operate. The shim allows you to:

• Distribute the load over a wider bearing surface.
• Compensate for ground irregularities and ensure a certain levelness.
• Avoid direct contact with damp ground, limiting moisture rise into the floor.
• Facilitate installation without heavy earthworks.
• Protect the ground (lawn, paving) by preventing marks and subsidence.

With a working load of 2.1 tonnes per shim, four shims can support a container whose total weight remains within permissible limits, provided the ground is sufficiently load-bearing.

Uses of the container shim

In the construction sector

Site welfare units and site offices are often installed on temporary, unstabilized ground. Shims allow a container to be placed quickly without pouring a slab, while ensuring a sufficiently stable base to accommodate personnel and equipment. They also facilitate subsequent relocation of the container at the end of the project.

In events

Containers are used as ticket offices, dressing rooms, control rooms or technical rooms on undeveloped sites: lawns, sports fields, car parks. Shims prevent damage to the ground and allow quick removal at the end of the event. Their resistance to high-pressure cleaning is an asset for removing mud after a festival.

In agriculture and rural areas

Containers are used to store grain, animal feed, equipment or plant protection products. By slightly raising the structure, shims limit direct contact with damp ground and reduce moisture rise into the floor, thereby extending the container's service life.

In retail and logistics

Containers serve as storage annexes or temporary sales points on car parks or brownfield sites. Shims allow rapid installation, without works, and easy site restoration. They are also useful for shimming generators or prefabricated modules.

For individuals

The shim is useful for installing a garden container, workshop or storage unit on a lawn or slightly sloping ground. It avoids having to pour a slab and allows the container to be moved later.

Possible conversions and fit-outs

The container shim is not just a placement accessory: it opens the way to many conversions and fit-outs, by allowing a container to be installed on various terrains without heavy works.

Storage container on unprepared ground

Whether for storing site equipment, gardening tools or goods, a container placed on shims remains accessible and stable. Shims compensate for irregularities and prevent the container from sinking. For a 20-foot container, four shims are generally sufficient; for a 40-foot, it is recommended to provide six or eight to support the bottom rails at regular intervals.

Welfare unit or site office

Containers fitted out as offices or welfare units require a stable base for user comfort. Shims allow the container to be placed on slightly sloping ground by adjusting height through stacking (up to 5 shims). It is essential to check levelness with a spirit level so that doors operate correctly.

Technical room or sanitary facility

A container can be converted into a technical room (generator, compressor) or sanitary facilities. Shims ensure leveling and protection against ground moisture. In this case, it is advisable to use distribution plates under the shims if the ground is very soft.

Temporary sales space

For a pop-up store or sales stand, a container placed on shims can be installed quickly on a car park or public square. Shims prevent scratching the surface and facilitate dismantling. Stacking allows any slope to be compensated.

Workshop or garage

A workshop container on shims provides a raised working space, protected from moisture. Shims can be combined with distribution plates to improve load-bearing capacity. It is important to respect the working load of 2.1 tonnes per shim and to distribute heavy loads.

Temporary housing module

For temporary accommodation (construction site, event), a fitted-out container can be placed on shims. This allows installation without foundations, but local planning regulations should be checked. Shims must be arranged symmetrically and the container must be stabilized to withstand wind.

How to use the container shim properly

To get the most out of the shim, it is essential to follow a few good practices:

1. Check the ground's load-bearing capacity: on very soft ground, use a distribution plate or a bed of compacted gravel to prevent sinking.
2. Position the shims under the corner fittings or bottom rails: near the corners, to distribute forces and avoid putting weight on a less reinforced central area.
3. Ensure levelness: use a spirit level and stack the shims if necessary (max 5). Check that the shims are correctly aligned.
4. Distribute the load evenly: for a loaded container, arrange the shims symmetrically.
5. Check the condition of the shims: before each use, visually inspect for cracks, deformation or abnormal wear. A damaged shim must be replaced.
6. Do not exceed load limits: the maximum load on hard ground is 5.5 tonnes, but the usual working load is 2.1 tonnes. Take into account the ground type and load distribution.

Comparison with other shimming solutions

Wooden shims are easy to find and inexpensive, but they rot on contact with moisture, attract insects and lose their mechanical properties over time. Concrete shims are very resistant to compression, but heavy, difficult to move and brittle on impact. Steel plates are strong but rust, slip on certain surfaces and can mark them. Polypropylene shims like this one offer an interesting compromise: light (6 kg), durable, insensitive to moisture, impact-resistant and recyclable. Their shape and material allow stable stacking, which is not always the case with heterogeneous materials. Their resistance to high-pressure cleaning is an asset for outdoor or dusty environments.

Maintenance and durability

Maintaining the shim is simple. Polypropylene is not affected by water and withstands high-pressure cleaning up to 80 °C and 200 bar, which removes mud, soil residues or hydrocarbon splashes without degrading the material. It is advisable to store the shims away from direct sunlight over long periods, not because the material melts, but because UV eventually alters the surface appearance of most plastics. Regular visual inspection helps identify cracks, deformation or abnormal wear that could reduce load capacity. A cracked or crushed shim must be replaced.

At end of life, polypropylene is recyclable, which limits environmental impact. The shim is therefore a durable, reusable accessory with low maintenance requirements.

Points of vigilance and regulations

From a regulatory standpoint, placing a container on private land generally falls under planning law. In France, a container used as a storage unit or dwelling may be subject to authorization depending on its surface area, height and duration of installation. It is advisable to check with the local planning department before any installation. Shims do not exempt you from complying with local rules, but they facilitate placement in line with good practices, particularly regarding stability and safety.

For professional use, the employer must ensure that the installation does not present a risk of tipping or subsidence, in accordance with the general prevention principles of the French Labour Code. Particular attention should be paid to wind-exposed areas, where an empty container may be susceptible to overturning if the shims are not correctly arranged or if the container is not ballasted.

It is also important to remember that shims are not securing devices. They do not replace straps, chains or twist-locks used to secure a container on a chassis or on a ship. Their role is limited to static placement on the ground.

How many shims should you plan for?

The number of shims depends on the container size and the nature of the ground. For a standard 20-foot container, four shims are generally sufficient if the ground is homogeneous. For a 40-foot container or for terrain with irregularities, it may be useful to provide additional shims to support the bottom rails at regular intervals. On very soft ground, using distribution plates or a bed of compacted gravel improves load-bearing capacity and prevents gradual sinking. It is recommended to provide a sufficient number of shims to equip the four corners of the container, or more if the container is long or the ground is uneven.

Adapting placement to the ground type

The shim's versatility does not exempt you from adapting implementation to the terrain encountered. Each ground type presents specific constraints that must be anticipated to guarantee the stability of the assembly.

Compacted earth or clay soil

These soils are sensitive to moisture: they swell, shrink and lose load-bearing capacity after a period of rain. It is prudent to excavate slightly, compact and lay a layer of gravel before installing the shims. Without this precaution, gradual sinking can unbalance the container and stress its structure.

Gravel and compacted sand

Gravel drains well but remains mobile. Shims tend to sink slightly into it under concentrated load. A distribution plate under each shim, or a bed of gravel compacted with a vibrating plate, significantly improves long-term stability. Compacted sand must be stabilized, otherwise it shifts laterally.

Concrete, asphalt and paving stones

These are the most favorable grounds: they offer high load-bearing capacity and good flatness. The shim expresses its maximum load of 5.5 tonnes on them. On paving stones, however, it should be checked that the elements do not move under load, as an unstable paving stone can create a hard point or local tipping.

Sloping terrain

Stacking shims (up to 5 units) compensates for a moderate slope, but you should never settle for unstable stacking. The shims must be perfectly aligned and, if the slope is too steep, earthworks or concrete pads are preferable. A container placed askew abnormally stresses its corner fittings and can cause its doors to deform.

Common mistakes to avoid

Even with a well-designed accessory, certain implementation errors reduce the safety and durability of the installation.

• Placing shims only in the center: this transfers the load to a floor area that is not reinforced for it. The corner fittings and bottom rails are the support points intended by the container's design.
• Neglecting levelness: even a slight defect complicates door operation and creates permanent stresses in the structure.
• Using a damaged shim: a crack, crushing or permanent deformation reduces residual strength without necessarily being visible.
• Confusing shimming and securing: shims stabilize a stationary container, they do not secure it for transport.
• Forgetting wind: an empty container is light and can tip over in a gust if not correctly shimmed or ballasted.

Conclusion

The recycled polypropylene container shim is a simple, robust and versatile accessory. It allows a container to be placed under good conditions on most grounds, without heavy earthworks. Its technical characteristics – dimensions of 40 × 26 × 45 cm, weight of 6 kg, maximum load of 5.5 tonnes on hard ground, working load of 2.1 tonnes, safety factor of 1.5, stacking up to 5 units, resistance to high-pressure cleaning – make it reliable equipment for both individuals and professionals. It is part of a safety and durability approach, complementing a check of the terrain and compliance with local planning rules. Sold individually at €38, it is a modest investment to facilitate installation and extend the service life of a container.