Resin injection underpinning involves drilling small holes beside or through a footing and injecting an expanding resin into the ground beneath. The resin fills voids and compacts and stiffens the soil, improving its ability to carry the foundation. It is quick and causes little disruption, but it is not suitable for every soil or every cause of movement; a chartered structural engineer decides whether it fits your property.
How does resin injection work?
A grid of small-diameter holes is drilled down into the ground under the footing at depths and spacings set out in the engineer's design. Two-part resin is pumped in, where it reacts and expands, pushing into voids and loose material and compressing the surrounding soil. Monitoring during injection checks how the ground and the building are responding. The result is firmer ground under the existing foundation, without excavating beneath it.
Because there are no deep trenches, no large volumes of concrete and limited muck-away, resin injection is one of the least disruptive options we offer as part of our underpinning and subsidence repair in Liverpool. That convenience is exactly why it needs an honest assessment first: it only helps where the ground problem is one that resin can address.
When can resin injection be a good option?
- Voids or loosened ground under a footing, for example after a leaking drain has washed fine material away, once the drain has been repaired.
- Looser granular soils that the engineer judges will respond well to compaction.
- Localised problems under part of a wall or a slab, such as some sinking floor cases.
- Situations where excavation would be very disruptive, or access for digging is poor.
When is resin not the right answer?
- Shrinkable clay movement driven by trees or long dry spells, where the problem lies deep in the clay.
- Where firm ground is too deep for the treated zone to make a real difference, which may point to mini-piled underpinning.
- Where the existing footing itself is inadequate or damaged and needs replacing or extending, as with mass concrete underpinning.
- Where the cause, such as a leaking drain, has not been dealt with yet.
| Resin injection | Mass concrete | Mini-piled | |
|---|---|---|---|
| What it does | Improves ground under the existing footing | Extends the footing down to firmer ground | Carries the wall on piles to deep firm ground |
| Excavation | Small drilled holes | Bays dug under the footing | Pile bores plus needles or beams |
| Typical time on site | Often days | Usually weeks | Usually weeks |
| Ground it tends to suit | Voided or loose ground | Firm ground at moderate depth | Deep, soft, made or tree-affected ground |
Timescales are general and depend on the property, method and permissions. MyJobQuote describes resin injection as often taking only days, compared with about 3 to 5 weeks for most traditional underpinning jobs.
What does the process involve?
- Find the cause. A CCTV drain survey and, where the engineer asks, a soil and site investigation to see whether the ground suits resin.
- Repair the cause. Leaking drains repaired first through drainage-related subsidence work, otherwise the ground can wash out again.
- Design. The engineer sets injection points, depths and the monitoring needed.
- Approvals. Building Control and, where the Party Wall etc. Act 1996 applies, notices through a party wall surveyor.
- Injection. Resin injected in stages with the building monitored throughout.
- Review and repair. The engineer reviews the results; cracks are then repaired and the work signed off as applicable.
If your property is part of an insurance claim, the insurer and its engineer decide on the repair method, including whether resin is used. Do not attempt to inject or fill under foundations yourself.
What should you ask before agreeing to resin injection?
Because resin is quick and tidy, it is sometimes offered before anyone has worked out what is wrong with the ground. Before agreeing to any scheme, it is reasonable to ask what investigation the recommendation is based on, what the engineer believes caused the movement and whether that cause has been removed, how the building will be monitored during and after injection, and what happens if monitoring shows movement continuing. A clear answer to each of those is a good sign that resin has been chosen for the right reasons rather than for convenience.
Where do we see resin being considered locally?
Resin conversations often start with a drain. Older properties with long runs of clay drainage can develop leaks that soften or wash out ground under a corner or a rear wall, and sandy coastal ground, as found in parts of Southport and Crosby, is the kind where washed-out fines are a typical concern. Inland, in places like Maghull, extended later homes sometimes raise similar questions about ground under one section. In every case, investigation decides whether resin is suitable.
What affects the cost?
The number and depth of injection points, the volume of resin, the length of wall or area of floor, any drain repairs, investigation and monitoring, access, and making good afterwards. Resin is priced against the engineer's design, so we do not quote a figure before we know what the ground needs.
Wondering whether resin could work for you?
Call 07777 659786 or use the form. Tell us about the cracks, any drain problems and whether an insurer is involved, and we will call back to discuss local foundation repair options across Merseyside.
Frequently asked questions
Is resin injection as good as traditional underpinning?
It is a different technique rather than a better or worse one. Resin improves the ground beneath the existing footing; traditional underpinning takes the foundation down to deeper ground. Which suits depends on the soil, the depth of the problem, the cause and the loads. The structural engineer decides, based on investigation rather than preference.
Does resin injection work on clay soils?
Shrinkable clay that moves with seasonal moisture changes or tree roots is often not a good candidate, because the movement comes from deep within the clay rather than from voids or loose ground. Resin tends to suit looser or voided granular ground. The engineer reviews the soil information before deciding whether resin is appropriate.
Can we stay at home during resin injection?
Usually yes. Resin injection is carried out through small drilled holes with portable equipment, so there is little excavation and disruption is generally limited. Some work may be inside if internal walls or floors are involved. We explain exactly what will happen and for how long before work starts.
Will resin injection fix the cracks in my walls?
No. Resin works on the ground, not the masonry. Once the engineer is satisfied the ground has been improved and movement has stopped, cracks are repaired separately, often by stitching and repointing. If a leaking drain caused the problem, it must also be repaired or the ground may be washed out again.
How long does resin injection take?
Resin injection is often a matter of days on site, much quicker than traditional underpinning. The overall timetable also includes investigation, the engineer's design, Building Control and any party wall matters, which can take longer than the injection itself. It depends on the property, the ground and the permissions needed.