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Ground Movement Australia. Independent Advice. Clear Answers. Confident Decisions.

For homeowners with two quotes

Traditional underpinning or polyurethane resin injection.

Most people arrive here with cracks in the walls and two very different proposals. The methods are not interchangeable. Neither is the right repair until you know whether the house is going down, coming up, or moving with the seasons.

Talk it through before you commitHeave or subsidence

The short version

Speed and price are not the decision.

Traditional underpinning puts new support under a footing. Polyurethane resin injection treats the ground through small holes, and can lift something that has dropped. One is slow and disruptive. The other is often sold as quicker and cheaper. Both are often bought for a crack that has not been explained.

Ground Movement Australia does not sell either method, and we do not design them. This is the comparison we would want a homeowner to have before the deposit is paid.

Traditional underpinning

New support under the footing.

Mass concrete underpinning digs sequential pits under the existing footing and fills them so the load is carried lower. Pier and screw-pile systems do the same job with a different construction: they take the load to deeper or firmer ground. Done properly, it is a structural scope, usually designed by an engineer.

Where it earns its place

  • The footing has lost support, or was never adequate for the ground it sits on.
  • An engineer wants the load taken below fill, or below the clay that keeps changing moisture.
  • The whole of the affected structure is dealt with, not one corner that looks bad in a photo.

The costs that are not on the first page of the quote

  • Excavation, access, and putting gardens, paths and floors back.
  • Time. A house is often a building site for days or weeks, not an afternoon.
  • On reactive clay, treating only the low-looking part can pin that part while the rest of the house keeps moving with the seasons. The next crack opens beside the new work.
  • It does not repair a leak, bad drainage, or a tree. If the ground is heaving, a scope written for a drop is the wrong scope.

Polyurethane resin injection

Resin in the ground, sometimes a lift.

Expanding polyurethane is injected through small holes. It fills voids, compacts loose soil as it expands, and on some jobs lifts a slab, a path or a footing back toward level. Houses often stay occupied. The mess is usually far less than excavation.

Where it earns its place

  • A void or loose ground under a slab or path that has actually dropped.
  • Tight access, where digging under the house is impractical.
  • A limited relevelling, once someone has shown the movement is downward and has stopped, or will be controlled.

The limits that the brochure leaves out

  • It treats the soil it reaches. It does not, by itself, carry the house down to stable ground beneath clay that will shrink and swell again.
  • The lift can be hard to limit. An over-lift is not easily undone.
  • If the “low” side never fell — because the middle or the other side rose — lifting it makes the house worse. Resin does not find a leaking pipe.
  • Warranties are often about the product, not about the house never moving again. A day on site is not the same thing as a permanent result.

Side by side

The same crack. Two different promises.

What it does

Traditional. Builds new support under the existing footing, with concrete or with piers taken to firmer or deeper ground.

Resin injection. Injects expanding polyurethane into the ground to fill voids, tighten loose soil, and sometimes lift a slab or path.

Disruption

Traditional. Excavation, spoil, noise, and reinstatement of gardens, paths or floors. Living through it can be difficult.

Resin injection. Small injection points. Often no large excavation. People frequently stay in the house. Internal floors are sometimes drilled when there is no access underneath.

Time

Traditional. Days to weeks, depending on how much of the house is treated and how the concrete or piles are sequenced.

Resin injection. Often quoted as a day or two for a residential job. That speed is not evidence the method is the right one.

Reactive clay

Traditional. Can be designed to found below the soil that seasonally shrinks and swells. Underpinning only part of the house can leave the rest moving.

Resin injection. Treats the ground it is injected into. It does not, by itself, found the house below the depth where the clay keeps moving.

If the house is heaving

Traditional. A scope written for a drop does not answer ground that is rising. Deeper footings are an engineer’s question, not an automatic cure.

Resin injection. Lifting a point that only looks low, because something else has risen, increases the distortion. Resin does not stop the water.

Who is accountable

Traditional. Usually designed and certified by an engineer, and often subject to a building approval. That depends on the state and the work.

Resin injection. Sometimes offered as a ground treatment without that design. Whether approval is required still depends on the state and what is being done.

Where either quote is the mistake

Both fail in the same way: they assume the house has dropped.

The movement is seasonal

Reactive clay shrinks in a long dry spell and swells after prolonged rain. Freezing one side of that cycle in concrete, or filling it with resin, does not stop the soil.

The low point is not the point that moved

Edges lower than the middle can be edges that fell, or a middle that rose. Wet edges can lift and make the middle look sunken. A level plan does not contain the direction.

The cause is still there

A leaking pipe, water against the house, or a large tree taken out can be the reason the ground is moving. A structural product placed over that cause is a second bill, not a solution.

Some houses do need one of these repairs. The costly version is signing the quote that matches the contractor’s method before anyone has shown the direction of movement. The person selling resin and the person selling piers are not neutral about which box you tick.

Before you choose

Five things worth having before a deposit.

  1. 1

    The pattern

    Cracks, floors, doors and external concrete, read together. Not one photograph.

  2. 2

    The levels

    A shape of the building, understood as difference, not yet as direction.

  3. 3

    The history

    Drought, leaks, drainage, trees removed, extensions, and any earlier repair.

  4. 4

    Time, if one visit cannot tell

    Daily monitoring through a change in the weather, so a cycle is not mistaken for a failure.

  5. 5

    An engineer, if the scope is structural

    Design and certification stay with the qualified professional. GMA does not sign that.

Book an inspectionSee daily monitoring

Questions homeowners ask

Do cracks in walls mean I need underpinning?

No. Cracks, sticking doors and sloping floors mean something has changed. They do not tell you the house has subsided, and they do not tell you which repair to buy. Many cracks are seasonal, related to moisture, or not a foundation problem at all.

What is the difference between traditional underpinning and resin injection?

Traditional underpinning builds new support under an existing footing, usually with concrete or piers, often to deeper ground. Polyurethane resin injection pumps an expanding resin into the soil through small holes to fill voids, compact loose ground, and sometimes lift what has dropped. They are different methods. Calling both “underpinning” does not make them the same repair.

Is resin injection cheaper than underpinning?

It is often quoted as less money upfront, because there is less digging, less time on site and less reinstatement. A full traditional underpinning is usually a larger building job. The lower quote is not the lower cost if it treats the wrong movement and the house keeps moving.

Is polyurethane resin injection permanent?

It can fill a void and it can lift a slab that has dropped. It does not, by itself, carry the house below the clay that keeps shrinking and swelling. On reactive sites the ground can keep moving with the weather. Ask what is actually guaranteed. A promise that the resin will not shrink is not a promise that the house will never move again.

Which is better on reactive clay?

Neither, until the mechanism is known. Reactive clay goes down as it dries and up as it wets. Pinning only the part of a house that looks low can leave the rest free to keep moving. Injecting resin under a part that has risen, or over a leak that is still running, can make the shape worse. The clay does not care which product was sold.

Can either method fix heave?

Heave is the ground coming up, often from a leak, wet soil against the house, or clay re-wetting after a tree is removed. A repair that assumes the house has dropped fights the wrong movement. The water, the drainage or the change in the garden has to be dealt with. An engineer may still recommend a structural scope. That is a different decision from buying a lift.

How do I know if my house is subsiding?

You know the ground is going down only if the direction has been established, not because a crack is wide or a floor feels out of level. One set of levels shows which part is higher today. It does not show which part moved. A history of the house, the crack pattern, and readings over time are what separate subsidence, heave and a seasonal cycle.

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