Complete Buying Guide: How to Choose a Container Chock

Why use a container chock?

A shipping container, whether 20 or 40 feet, is designed to rest on its four reinforced corners, called corner castings. Placed directly on uneven, soft, or wet ground, it risks deforming, tipping, or sinking. The container chock is a simple accessory that distributes loads, compensates for unevenness, and slightly raises the container to limit contact with ground moisture. It thus contributes to personal safety and the longevity of the installation, whether for temporary storage, a site office, a technical room, or a light dwelling.

Criteria for choosing a container chock

1. Material: polypropylene, wood, rubber, or concrete?

The choice of material determines durability, strength, and ease of implementation. Here is a comparison of common solutions:

• Recycled polypropylene: resistant to weather, impacts, and most chemicals. Does not rot, does not attract insects, recyclable at end of life. Lighter than concrete, stiffer than rubber. Ideal for semi-permanent installations or frequent repositioning needs.
• Solid wood: economical and easy to cut to size, but sensitive to moisture, wood-boring insects, and splinters under heavy load. Load capacity varies by species and quality. Limited lifespan outdoors.
• Recycled rubber: excellent grip, but generally more flexible and less suited to heavy, concentrated static loads from a container. Often used for chocking vehicle wheels.
• Concrete or foundation blocks: very high load-bearing capacity and great stability for permanent installations, but heavy, difficult to move, and require ground preparation work.

The polypropylene chock sits in between: more durable than wood, more stable than rubber, more mobile than concrete. It is particularly suitable for stabilized ground (concrete, asphalt, compacted gravel) and can be used on soft ground with caution.

2. Dimensions and bearing surface

The dimensions of the chock determine its bearing surface and thus its ability to distribute the load. A wider or longer chock distributes pressure better, which is useful for very heavy containers or soft ground. Conversely, a compact chock is easier to transport and store, but offers a smaller bearing surface.

Height is also an important criterion. A low chock (2 to 3 cm) is sufficient for simple anti-roll chocking. A taller chock (7 to 10 cm) significantly raises the container, which can facilitate access or ventilation, but may destabilize the assembly if not properly distributed. A height of 4.5 cm, like that of the EXCLUSIVELY WEB chock, offers an interesting compromise: it creates an air gap under the container to limit contact with moisture, without making access difficult or destabilizing the assembly.

3. Maximum load and working load

Two values should be distinguished:

• Maximum load on hard ground: this is the load the chock can withstand before failure, under ideal conditions. It is generally given for hard and stable ground.
• Working load: this is the recommended load in normal use, with a safety margin. The safety factor (often 1.5) indicates the ratio between maximum load and working load.

For a standard container, it is essential not to rely on maximum load alone. An empty 20-foot container weighs about 2.2 tonnes, a 40-foot about 3.8 tonnes. Once loaded, the weight can reach several tens of tonnes. The chock alone cannot support the entire load of a loaded container; it is designed to stabilize and distribute forces, not to replace concrete blocks or foundations. Therefore, check the ground's load-bearing capacity and use a sufficient number of chocks, respecting the working load indicated by the manufacturer.

4. Stackability and stability

Some chocks are stackable, allowing fine height adjustment based on ground irregularities. Maximum stacking is generally limited (e.g., up to 5 units) to ensure stability. Beyond two or three chocks, it is advisable to check the flatness and load-bearing capacity of the assembly, as stacking reduces lateral stability. Exceeding the manufacturer's limit is not recommended.

5. Weather and UV resistance

For outdoor installation, the chock must resist UV, rain, frost, and temperature variations. Treated polypropylene offers good UV aging resistance, unlike wood which can rot or degrade. A temperature resistance of 80 °C allows cleaning with a pressure washer (up to 200 bar), which facilitates maintenance.

6. Ease of handling and storage

The weight of the chock is an important criterion if you need to move it frequently. A 6.2 kg polypropylene chock can be handled by one person without specific equipment. Conversely, a concrete chock can weigh several tens of kilos and require lifting equipment. Storage should also be considered: stackable chocks take up less space.

How to determine the number of chocks needed?

A standard container rests on four reinforced corners. It is therefore logical to place one chock under each corner, i.e., four chocks for a container. On soft ground, it may be useful to add chocks under the longitudinal beams to prevent the floor from flexing. In this case, ensure all chocks are at the same height to avoid creating stress points. For a 40-foot container, some users add intermediate chocks under the beams, bringing the total to six or eight. The number therefore depends on the container's weight, the nature of the ground, and load distribution.

Mistakes to avoid when buying

• Neglecting ground load-bearing capacity: a chock, even a very strong one, cannot compensate for unstable ground. On soft ground, load capacity is reduced and requires case-by-case evaluation.
• Confusing maximum load and working load: maximum load is a failure value, not a usage value. Always use the working load to size your installation.
• Using untreated wooden chocks: they rot quickly and can attract insects. Prefer a durable material like polypropylene.
• Stacking beyond limits: respect the maximum stackability indicated by the manufacturer. Beyond that, stability is no longer guaranteed.
• Forgetting to check the condition of chocks: a cracked or deformed chock must be replaced. Regular visual inspection is advised.

Comparison of stabilization solutions

To help you choose, here is a comparison table of the main solutions:

• Polypropylene chock: durable, weather-resistant, lightweight, recyclable. Suitable for semi-permanent installations and frequent moves. Affordable price (about €14 per unit).
• Wooden chock: economical, cut to size, but sensitive to moisture and insects. Limited lifespan.
• Rubber chock: good grip, but less suited to heavy static loads. Often used for wheel chocking.
• Concrete block: very high load-bearing capacity and stability, but heavy, difficult to move, and requires preparation work. Reserved for permanent installations.

Installation and maintenance: best practices

Installing a chock is simple and requires no special tools. Slightly lift the container using a jack or forklift, then slide the chock under the relevant support point. For optimal stability, use one chock per corner. On very uneven ground, you can stack up to five chocks to raise a corner, but check that the stack remains stable and the load is properly distributed.

Maintenance is minimal: cleaning with a water jet or pressure washer (up to 200 bar and 80 °C) is enough to remove mud and dirt. Avoid strong solvents that could damage the surface. For prolonged storage, store chocks away from direct sunlight to limit UV aging, although the material is treated to withstand weather. Regular visual inspection is advised: check for cracks, crushing, or deformation. If a chock shows a visible defect, replace it.

Regulations and safety

The transport and installation of shipping containers in France are subject to some rules. The container itself must meet ISO 668 and ISO 1496 standards, which define dimensions, loads, and tests. For a permanent installation, a planning permission may be required, especially if the container is used as a dwelling or ancillary premises. Chocks are not subject to specific regulations, but their use must guarantee the safety of people and property.

In road transport, the container must be secured to the truck chassis with twist-locks, not simply placed on chocks. Chocks can be used during temporary storage at the carrier's site, but do not replace regulatory securing devices. In maritime transport, containers are secured according to IMO rules and shipping company requirements; chocks can be used to secure goods inside the container, but not to stabilize the container itself on the ship.

Use cases: for whom and for what?

The container chock is aimed at a wide audience:

• Logistics and construction professionals: stabilization of site camps, storage containers, or site offices on dirt or gravel ground.
• Events: rapid installation of container dressing rooms, pop-up bars, or storage spaces on various surfaces (grass, gravel, asphalt).
• Farmers: storage of grain, tools, or equipment, avoiding direct contact of the floor with wet ground.
• Individuals: conversion of a container into a workshop, garden office, or light dwelling, as an economical alternative to concrete slabs.

In all cases, it is essential to respect allowable loads and provide a sufficient number of support points.

Adapting the chock to the container type

Not all containers are alike, and their structural constraints vary. It is useful to know the specifics of the main types to choose the right number and positioning of chocks.

Dry and high cube containers

These are the most common models. A standard 20-foot dry container weighs about 2.2 tonnes empty, a 40-foot about 3.8 tonnes. The high cube, 30 cm taller, has an identical structure but a slightly higher center of gravity. Chocks are placed under the four corner castings, and possibly under the beams for heavy loads. The additional height of the high cube does not affect ground chocking.

Reefer containers (refrigerated)

A reefer container is significantly heavier empty (about 3 tonnes for a 20-foot) due to its refrigeration unit and insulation. It requires particular attention to ground flatness and under-floor ventilation. Chocks must be perfectly level to avoid stressing the chassis. A reefer in operation must remain powered and must not be moved without precaution.

Open top and flat rack containers

These containers have removable walls or roofs, and sometimes different support points. A flat rack, without walls, rests on a reinforced platform that may require wider chocks. An open top, with its tarpaulin, is chocked like a dry but may be more sensitive to infiltration: slightly raising the container with chocks limits contact with ground moisture. In all cases, consult the container specifications and, if needed, seek professional advice.

Stacked containers

When several containers are stacked, chocks are generally used only under the bottom container, as corner castings are designed to transmit loads vertically. Stacking containers must follow safety rules: never exceed the recommended height and always use twist-locks between levels. Ground chocks must then support the cumulative load, requiring an adapted number and sizing.

Choosing the chock according to ground type

Ground load-bearing capacity is a determining factor. Here is how to adapt your choice:

• Hard and stable ground (concrete, asphalt, slab): a standard polypropylene chock is sufficient, with one chock per corner. The maximum load indicated by the manufacturer can be used as a reference, while remaining within the working load range.
• Compacted ground (gravel, compacted crushed stone): load-bearing capacity is good but can degrade with moisture. Provide wider chocks to distribute pressure and regularly check for sinking.
• Soft ground (dirt, sand, grass): load capacity is reduced. Use larger chocks, add support points under the beams, and consider a stabilization layer (compacted gravel, distribution plate) under each chock.
• Sloped ground: chocks must be combined with an anti-slip system or grooved plates. Stacking should be avoided as much as possible, as it reduces lateral stability.

In all cases, a visual inspection before and after loading is recommended.

Recycled polypropylene: an environmental choice

The polypropylene used for chocks is often made from recycled materials, contributing to the recovery of plastic waste. At end of life, the chock itself can be recycled, limiting its environmental impact. Compared to treated wood, which may contain preservation chemicals, polypropylene does not release toxic substances into the soil. It is also immune to rot and fungi, making it a relevant choice for sustainable installations, especially in wet or coastal areas where wood resists poorly. For projects concerned about their ecological footprint, choosing a recyclable chock is a simple but consistent gesture.

Budgeting for stabilization equipment

The price of a container chock varies by material and dimensions. A good quality polypropylene chock generally costs between €10 and €20 per unit. For a standard container, count four chocks, i.e., a budget of €40 to €80. If you add chocks under the beams, the budget can reach €100 to €150. This cost remains modest compared to the potential damage of a poorly stabilized container: floor deformation, accelerated corrosion, tipping. Investing in suitable chocks is therefore a long-term saving. Also consider providing a set of spare chocks, as a damaged chock must be replaced immediately.

Conclusion: choosing the right container chock

Choosing a container chock relies on several criteria: material, dimensions, working load, stackability, and weather resistance. Recycled polypropylene offers an excellent compromise between durability, lightness, and cost. Before buying, check your ground's load-bearing capacity, your container's weight (empty and loaded), and the number of chocks needed. Remember that the chock is a stabilization accessory, not a lifting device: it does not replace concrete foundations for extreme loads. By following these principles, you will extend the life of your container and enjoy a safe and durable installation.