When a mobile crane, aerial work platform, or heavy plant machine deploys its outriggers, those four contact points carry an enormous concentration of load. Without the right outrigger pads, that load can punch through tarmac, damage underground services, sink into soft ground, or — in worst-case scenarios — cause a machine to tip. Choosing the correct crane stabiliser pads is not just an operational decision; it's a fundamental safety requirement.
This guide covers everything UK plant operators, lifting supervisors, and site managers need to know about selecting, sizing, and using outrigger pads safely.
Why Outrigger Pads Are Critical
Mobile cranes and heavy plant machines generate extremely high point loads at outrigger feet. A 50-tonne crane can impose loads of 30–80 tonnes per outrigger foot depending on the lift configuration. Tarmac, asphalt, and compacted hardcore can appear solid but have surprisingly low bearing capacities — often as low as 100–200 kN/m².
Outrigger pads spread that concentrated point load over a much larger area, reducing ground pressure to levels the underlying surface can safely support. The physics is straightforward: double the pad area and you halve the ground pressure. Use the right pad, and a 60-tonne point load becomes manageable on a standard roadway.
Types of Outrigger Pads
1. UHMWPE (Ultra-High-Molecular-Weight Polyethylene) Pads
UHMWPE outrigger pads have become the industry standard for crane and plant stabilisation in the UK. The material offers a remarkable combination of properties:
- Exceptional compressive strength: Resists crushing under extreme loads
- High impact resistance: Won't crack or shatter under dynamic loading
- Self-lubricating surface: Won't bond to the ground or outrigger foot
- Lightweight: Up to 8x lighter than steel pads of equivalent load capacity
- Chemical and moisture resistance: Suitable for contaminated ground, wet conditions
- UV stable: No degradation in outdoor storage or use
- Colour-coded: Available in different colours for load rating identification
UHMWPE pads are available from small 500mm × 500mm options up to 1,500mm × 1,500mm or larger, and in thicknesses from 25mm to 150mm.
2. Composite Outrigger Pads
Composite pads use fibre-reinforced polymer materials to achieve high strength-to-weight ratios. They offer:
- Very high compressive and shear strength
- Lightweight handling — important for large pads
- No moisture absorption
- Higher cost than UHMWPE but comparable performance
Composite pads are particularly popular for specialist lifting operations where maximum load capacity per unit of weight is critical.
3. Timber/Oak Cribbing
Traditional hardwood cribbing (oak or similar dense timber) has been used for decades and remains in use on some sites. However, timber has significant drawbacks compared to modern engineered pads:
- Inconsistent strength — affected by moisture, age, and grain direction
- Can split, splinter, or crack under dynamic or eccentric loads
- Cannot be visually inspected for internal defects
- Heavy for its load capacity
- Absorbs moisture — may swell, rot, or freeze
While timber cribbing is not prohibited, most modern lifting plans specify UHMWPE or composite pads for predictability and safety.
4. Steel Outrigger Pads
Heavy steel plates offer very high load capacity but at the cost of extreme weight. A 1m × 1m steel plate suitable for crane work may weigh 250–500 kg, requiring crane or telehandler assistance to position. Typically used only in static industrial environments or where weight is not a constraint.
Load Spreading: The Maths That Keeps Your Crane Upright
Understanding load spreading is essential to specifying the right pad. The calculation is:
Ground Pressure (kN/m²) = Outrigger Load (kN) ÷ Pad Area (m²)
For example: A 400 kN outrigger load on a 0.5m × 0.5m pad = 1,600 kN/m² — far beyond the bearing capacity of most surfaces. The same load on a 1.0m × 1.0m pad = 400 kN/m² — still high, but potentially within the capacity of reinforced concrete or solid rock. On a 1.5m × 1.5m pad = 178 kN/m² — manageable on most prepared ground.
Always obtain the maximum outrigger load from the crane manufacturer's capacity chart for the specific lift configuration, not the crane's rated lift capacity.
How to Choose the Right Size
When selecting outrigger pads for UK crane and plant use, consider:
Ground Type
- Rock/reinforced concrete: High bearing capacity — smaller pads may suffice
- Tarmac/asphalt: Moderate bearing capacity — verify and use adequately sized pads
- Compacted hardcore: Variable — always use generous pads
- Soft/disturbed ground: Low bearing capacity — large pads essential; may need ground investigation
- Over voids/services: Consult a structural engineer regardless of pad size
Pad Thickness
Thickness determines the pad's ability to spread load through its depth (bending stiffness). Thicker pads distribute load more widely:
- 25–50mm: Light plant, telehandlers, MEWPs
- 75–100mm: Medium cranes and larger plant
- 100–150mm: Heavy lifting operations, maximum spread requirements
How Many Pads?
Most mobile cranes have four outriggers — one at each corner. Stacking pads to achieve greater thickness is common practice, but:
- All pads in a stack should be the same material and size
- Stacks of more than 3–4 pads are generally not recommended without engineering guidance
- The outrigger foot should be centred on the top pad with clear margins on all sides
Outrigger Pad Safety Requirements
Under UK lifting operations regulations (LOLER) and the requirements of the Construction (Design and Management) Regulations, lifting plans must specify ground support requirements. Best practice includes:
- Lifting plan to include outrigger pad specification
- Ground bearing capacity assessment (visual minimum; intrusive survey for critical lifts)
- Pads to be positioned by a slinger/signaller — never by the crane
- Visual inspection of pads before and after each use
- Withdraw from service any pad showing cracks, splits, or deformation
- Storage flat, off the ground, to avoid warping
View the full range of outrigger pads at Barriers Co — including UHMWPE stabiliser pads in all standard sizes and thicknesses, with next-day UK delivery available.
Frequently Asked Questions
What material is best for outrigger pads?
UHMWPE is the most widely specified material for outrigger pads in the UK due to its combination of high compressive strength, light weight, moisture resistance, and durability. Composite pads offer similar performance at higher cost.
How do I calculate the size of outrigger pad I need?
Divide the maximum outrigger load (from the crane's duty chart) by the bearing capacity of the ground. The result is the minimum pad area required. Always add a safety factor and consult a lifting engineer for critical lifts.
Can you stack outrigger pads?
Yes — stacking pads of the same size and material is standard practice to increase effective thickness. Limit stacks to no more than 3–4 pads unless specifically designed stacking systems are used.
How often should outrigger pads be inspected?
Visually inspect before every use. Any pad showing cracks, splits, deformation, or discolouration indicating heat damage should be withdrawn from service immediately.
Are UHMWPE pads suitable for use on soft ground?
UHMWPE pads can be used on soft ground but the underlying bearing capacity must be assessed. On very soft ground, even large pads may be insufficient — ground improvement or engineered hardstanding may be required.
Do I need a lifting plan to specify outrigger pads?
Yes — under LOLER, all lifting operations must be properly planned. The lifting plan must include ground support requirements including outrigger pad specification, positioning, and ground bearing capacity assessment.