What Is Concrete Levelling and Is It Right For Your UK Property?

Concrete levelling, as practised in the UK, means injecting expanding polyurethane resin beneath a sunken slab to lift it back to level. The work happens from underneath: no surface grinding, no screed overlay, no demolition.

The method has been used in the US since the 1980s and has grown substantially in the UK over the past fifteen years, driven initially by the industrial and commercial sectors where full slab removal means weeks of operational downtime. It's now well established for residential work too.

Why slabs sink in the first place

Concrete ground-floor slabs are not structural elements. They don't span gaps the way a reinforced beam does. They rest on the ground beneath them and transfer load directly into the sub-base. When the ground moves, the slab follows.

Ground movement beneath slabs has several causes in the UK:

Clay shrinkage. The most common cause across the South East, Midlands, and East Anglia. Clay soils lose volume as they dry, and the slab drops into the space created. The movement is often seasonal. See our deeper guide on why UK clay soils cause concrete to sink.

Soil washout. Water infiltrating through joints and cracks gradually removes fine particles from the sub-base, creating voids that enlarge over time. The slab eventually has no support across part of its area.

Made ground compaction. Many UK properties are built on ground that was previously filled. This fill continues to consolidate over decades, and slabs above it settle progressively.

Tree root desiccation. Mature trees on clay soils draw moisture from a wide radius. A slab within 15–20m of a mature oak or willow is at elevated risk, particularly during dry summers.

Understanding the cause matters because it affects whether re-treatment is likely and what preventive measures make sense alongside injection.

How the process works

A site survey comes first. A competent contractor will walk the area, use a level to quantify the settlement, tap the surface to map void extent, and assess drainage and sub-base condition before quoting. A quote issued without a site visit is an estimate, not an assessment. Our how it works page walks through the full sequence step by step.

On the day of works:

Drilling. Small holes (typically 12–16mm, about the size of a 10p coin) are drilled through the concrete in a grid pattern. Spacing depends on void extent but is typically 1–2m. The holes are positioned to maximise coverage of the void based on the tap survey.

Injection. Two-component polyurethane resin is mixed at the injection nozzle and pumped under controlled pressure. The two components react on contact and expand to fill the void, compress and stabilise the sub-base material beneath, and generate upward pressure that lifts the slab.

Lift monitoring. Operators place a level gauge at reference points around the injection area and monitor lift in real time. The expansion is measured and controlled: a 20–30mm lift might take several passes across the grid, injecting small volumes at each point and checking progress between passes. Overshooting is possible if the process is rushed.

Verification and reinstatement. Post-injection, the contractor confirms the lift achieved against target using a level. Holes are filled flush with mortar or colour-matched compound.

The resin is closed-cell, meaning it doesn't absorb water or degrade in the damp sub-base conditions typical of UK ground. It has a design life of 25 years or more.

Where it works well

• Residential driveways and paths where sections have dropped
• Garage floors that have settled at the entrance or mid-span
• Internal floor slabs in offices, retail units, and warehouses where a void has formed
• Loading bays and yard surfaces that have subsided under vehicle loading
• Patio slabs and garden steps that have settled against the structure
• Any situation where the concrete is structurally intact but no longer supported

Where it doesn't work

Spalled or crumbled concrete. If the slab has deteriorated to the point where it can't be injected through and lifted as a unit, it needs replacing first. The injection technique depends on the slab acting as a rigid unit that can be lifted intact.

Active water ingress from a known source. Resin fills a void. If a fractured drain or failed gully is continuing to wash out sub-base material, the cause needs fixing first or the void will reform.

Structural foundations. Resin injection addresses floor slabs. It doesn't underpin load-bearing walls, footings, or structural foundations. If a structural engineer is involved in a subsidence assessment, their scope is different from a levelling contractor's, and the two should not be conflated. See home subsidence for how the two interact.

UK-specific considerations

Britain's clay geology adds a dimension that doesn't apply in drier climates. In high-risk clay areas, the underlying soil continues to move seasonally, and a slab that's been levelled may experience further movement over subsequent years. This doesn't mean the treatment has failed; it means the ground is still active.

For most residential properties on moderate-risk clay, a single treatment provides a lasting result. On high-risk clay with active tree influence or persistent drainage issues, the expectation should be occasional re-treatment rather than a permanent fix. That remains far cheaper per occurrence than replacement: see our cost comparison guide for the full breakdown, or request a free survey for your property.