The short answer
Resin injection — sometimes called geopolymer or expanding-resin ground stabilisation — is usually a lower-cost and far less disruptive alternative to traditional underpinning where it is suitable, typically costing around £3,000–£15,000 for a domestic treatment, against £10,000–£35,000+ for conventional underpinning. Instead of excavating and pouring concrete, a structural resin is injected through small holes into the soil beneath the foundation, where it expands to fill voids, compact loose ground and re-level the foundation. It is often completed in a day or two with no large open trenches, which is why it is cheaper and quicker. However, it is not always appropriate: it suits certain soils and movement types but is unsuitable for clay shrinkage near trees or where deep, structural foundation support is required. A structural engineer and a ground assessment decide whether it is the right method at all.
Resin injection is a genuine alternative for the right ground conditions, not a universal substitute for underpinning. Where it suits, it is cheaper and quicker; where it does not, it is the wrong tool. The figures below are typical UK ranges for guidance.
Typical UK costs
- Resin injection treatment~£3,000–£15,000
- Vs traditional underpinningoften lower cost
- Typical durationaround 1–2 days
- Disruptionminimal — no large open trenches
- Suitabilitydepends on soil and movement type
How resin injection compares
- Cost: generally lower than mass concrete or piled underpinning because there is little excavation, less labour and a shorter programme.
- Disruption: small injection points rather than open trenches, so gardens, drives and floors are largely undisturbed.
- Speed: many domestic treatments are completed in a day or two.
- Limitation: it is a ground-improvement method, not a deep foundation. It does not suit clay shrinkage driven by trees, very deep movement, or cases needing engineered structural support to a stable stratum.
| Method | Typical cost | Disruption |
|---|---|---|
| Resin injection (where suitable) | £3,000–£15,000 | low — small injection points |
| Mass concrete underpinning | £10,000–£35,000 | high — open excavation |
| Mini-pile underpinning | £15,000–£50,000+ | high — rig + beams |
Indicative UK guidance. Sources: Checkatrade underpinning cost guide and structural engineering practice.
When resin is and is not appropriate
Resin injection works by stiffening and re-compacting the soil beneath a foundation, so it suits movement caused by loose or washed-out ground, minor settlement and certain made-up soils. It is not a substitute for underpinning where the cause is clay shrinkage around trees, where foundations must reach a deep stable stratum, or where the structural engineer concludes the foundation itself needs physical extension. Crucially, an insurer handling a subsidence claim, and Building Control, will expect the chosen method to be specified and justified by a qualified engineer after a soil investigation. Treat any contractor who recommends resin without that assessment with caution, because using it on the wrong ground can fail to stop the movement.
How the injection process works
Resin injection is fast and minimally invasive compared with excavation-based underpinning. Small injection tubes are inserted through the ground or floor at set points around the affected foundation, and a structural geopolymer or expanding resin is pumped in. The resin reacts and expands, filling voids in the soil, compacting loose ground and, in the right conditions, gently lifting and re-levelling the foundation. Specialists usually monitor the building with laser levels during injection so the lift is controlled and the structure is not over-raised. Because there are no open trenches, gardens, driveways and internal floors are largely left intact, and many domestic treatments are finished within a day or two with the building remaining occupied. That low disruption, and the short programme, is the main reason the method is cheaper than mass concrete or piling where it is genuinely suitable.
| Stage | What happens |
|---|---|
| Assessment | engineer + ground investigation confirm suitability |
| Injection points | small tubes set around the foundation |
| Resin pumped in | expands, compacts soil, fills voids |
| Monitoring | laser levels control any lift |
General UK guidance. Source: structural engineering practice and Checkatrade cost guide.
Guarantees, regulation and choosing a contractor
Because resin injection is a proprietary, specialist process, the quality of the contractor matters as much as the method. Reputable installers carry out a proper ground assessment, work to a structural engineer's brief, and offer an insurance-backed guarantee on the work, which is worth confirming in writing. The treatment should still be coordinated with Building Control where it forms part of a structural repair, and where it is part of a subsidence claim the insurer's engineer must specify and approve it. Be wary of any contractor who recommends resin from a quick look without a soil investigation, who promises it as a universal alternative to underpinning, or who cannot show the method is appropriate for your ground and the confirmed cause of movement. Used correctly on suitable soil it is an effective, lower-cost solution; used as a shortcut on the wrong ground it simply delays the proper repair.
It is also worth being realistic about how resin injection is marketed. Because it is quick, clean and proprietary, it is sometimes promoted as a simple alternative to underpinning for almost any cracked house, which overstates its range. The honest position is narrower: it is an effective ground-improvement technique for specific soils and movement types, confirmed by a structural engineer after a ground assessment, and a poor choice where the cause is clay shrinkage around trees or where deep structural support is needed. A reputable specialist will turn work away when the ground is wrong for it, rather than inject regardless. For that reason, the most useful thing a homeowner can do is treat resin as one option the engineer weighs against mass concrete and piling, not as a default because it is cheaper and less disruptive. Where it genuinely suits the soil it is excellent value; where it does not, the money is better spent on the method the ground actually requires.
The honest framing for resin injection is that it is a legitimate technique with a narrow window of suitability, not a universal shortcut, and the marketing around it sometimes blurs that line. Geopolymer resin works by expanding in the ground to compact loose soils and lift a slab or footing, which suits certain settlement problems — a sunken floor slab, or shallow movement over loose granular fill — and it is genuinely faster and less disruptive than digging. But it is not a substitute for traditional underpinning where the ground needs reaching down to a deeper competent stratum, where there is significant clay shrinkage near trees, or where a structural engineer has specified a designed foundation. Crucially, an insurer handling a subsidence claim, and Building Control, will both want the method to be appropriate to the diagnosed cause, and resin is not always accepted for an insured subsidence repair. So the sensible approach is to treat a resin quote the same way as any other: insist on a structural engineer's diagnosis first, confirm the method actually fits the cause, and be wary of any pitch that presents injection as a cheaper alternative to underpinning without reference to what the ground investigation shows.
Frequently asked questions
Is resin injection cheaper than traditional underpinning?
Where it is suitable, yes — typically £3,000–£15,000 against £10,000–£35,000+ for conventional underpinning, because there is minimal excavation and a much shorter programme. It is only lower cost when the soil and the cause of movement are right for it.
Is resin injection as good as underpinning?
For the right ground and movement type it can be an effective, low-disruption solution. It is not equivalent where deep structural foundation support is needed or where clay shrinkage near trees is the cause, so a structural engineer must confirm the method.
Will my insurer accept resin injection for a subsidence claim?
Possibly, if the appointed engineer specifies and justifies it after investigation. Insurers fund the method shown to be appropriate for the confirmed cause, so the diagnosis and engineering report come first.
Sources & further reading
- Checkatrade — underpinning cost guide
- RICS — subsidence guidance for homeowners
- ABI — subsidence and your home
Figures on this page are typical UK ranges drawn from published sources and depend on your specific property. They are guidance, not a quotation.