Resin injection vs traditional underpinning: which one actually suits your house?

If your slab or strip-footing home needs underpinning, you'll quickly meet two camps: crews selling excavated concrete underpinning and crews selling resin injection — each insisting theirs is the answer. Both are legitimate. Neither is right for every house. Here's the comparison the sales brochures skip.

How each method works

Traditional (mass concrete) underpinning is the hundred-year-old heavyweight: pits are excavated beneath the failed footing in a carefully staged sequence — never all at once — and filled with concrete, so the wall ends up founded on deeper, stable ground. It physically extends your footing downward past the problem soil.

Resin injection drills small (roughly coin-sized) holes and pumps an expanding structural resin into the ground beneath the footing. The resin fills voids, compacts weak soil, and — injected carefully in stages — can lift a sunken footing back toward level, with the lift monitored by laser as it happens. It treats the ground the footing sits on rather than deepening the footing itself.

The cost picture (2026)

• Traditional concrete underpinning: $1,500–$3,000 per lineal metre of wall. A single sunken corner (3–4 lm) might run $5,000–$12,000 of works; a full wall (6–10 lm) roughly $12,000–$24,000 before geotech and engineering.
• Resin injection: typically $4,000–$16,000 for a whole residential job. Small void-filling and single-corner lifts sit at the bottom of that band — often meaningfully cheaper than excavation for the same corner.
• Both need the same paperwork: a geotechnical report ($1,000–$3,000) and engineering ($500–$3,000), plus a building permit (VIC) or certifier approval (QLD).

Where resin genuinely wins

• Speed and tidiness. Most resin jobs finish in 1–2 days with no excavation, no spoil, and furniture still in the house. Traditional underpinning is days to weeks of staged digging and curing.
• Voids and loosened soil. Where washout from a leaking pipe or poor drainage has left voids or soft zones under an otherwise adequate footing, filling and compacting the ground is precisely the right treatment.
• Moderate re-levelling of a slab or footing that has settled tens of millimetres, in soils the resin suits.
• Access-hostile sites — courtyard walls, internal slab dips, tight boundaries where an excavator can't work.

Where traditional wins

• Deep or ongoing movement. If the footing needs to be founded deeper — reactive clay drying to depth, fill that never consolidated, soft strata — resin can't extend the footing downward. Concrete (or screw piers) can.
• Severe subsidence and heavy structures. Big settlements, double-brick walls, multi-storey loads: the proven, permanent, physically-deeper fix is still the default.
• Certainty. A mass concrete pin founded on verified ground at an inspected depth is about as arguable as construction gets. Resin outcomes depend heavily on soil suitability and operator skill.
• Wet or highly permeable ground, where resin placement is harder to control.

The third option: steel screw piers

Worth knowing before you pick a camp: screw piers ($3,500–$5,500 per pier, roughly one per 1.5–2 metres of wall) split the difference. Steel piers are wound down to refusal on solid strata and bracketed to the footing — deeper founding like traditional, far less excavation, and installation measured in days. They shine where stable ground sits deep (soft alluvial soils, fill sites) and where the engineer wants verified founding depth without weeks of staged pits. Plenty of well-designed jobs mix methods: piers on the worst corner, resin void-filling under the slab beside it.

Questions that sort the quotes

• "What did the geotech report say, and can I see it?" No soil report, no method credibility — for either camp.
• "Why this method for this soil and this cause?" The answer should reference your ground, your founding depth and what started the movement — not the truck in the driveway.
• "What warranty, in writing, and is it transferable?" Reputable operators in both camps offer long structural warranties; get the words.
• "What happens if the target lift isn't achieved?" Especially for resin re-levelling — the honest answer acknowledges limits.

The decision that actually matters

The method should fall out of the geotechnical report and the engineer's assessment — soil type, founding depth, cause of movement — not out of which company's ad you clicked first. A corner sunk over a broken stormwater pipe in sandy loam and a wall failing on deep-drying reactive clay are different problems wearing the same crack. Be wary of any outfit that only sells one method and has never once recommended the other: when your only tool is a resin pump, every house looks like a void.