If you own an older elevated house in Brisbane, you may have noticed vertical cracks in the brickwork underneath, usually where the brick walls meet the original concrete stumps.
Is the house sinking? Do the foundations need repairing? Should you be worried?
Not necessarily.
I recently inspected an older Brisbane home where the owner had exactly these concerns. I didn’t find evidence of a significant structural movement problem in the areas I inspected. The main issue was the way the lower-level brickwork had been built around the original concrete stumps.
Why Do Brick Walls Crack Next to Concrete Stumps?
Many older Brisbane homes were built as elevated timber-framed houses on concrete or timber stumps (engineers often call them piers). Over the years, owners have enclosed the space underneath to create garages, storage rooms or extra living areas, usually by building brick walls between the existing stumps.
The problem is that brickwork and concrete don’t move together. Brickwork expands and contracts with changes in temperature and moisture. Concrete stumps and their footings can also move slightly as ground conditions change.
When brickwork is built hard against the concrete with no flexible joint, those small movements show up as cracks. They usually appear as nearly vertical lines along the junction between the two materials. They may be narrow, but they can look alarming, especially when they run the full height of the wall.
What I Found During a Recent Inspection
The house was an elevated timber-framed home from around the 1960s. The lower level had been enclosed with rendered brickwork between the original concrete stumps.
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- Several vertical cracks, generally less than 3 mm wide, ran along the junctions between the brickwork and the stumps. Some had been patched before, and the cracking had come back.
- One concrete stump had a separate crack that had been roughly repaired and painted over. I tapped the concrete either side of the repair and it sounded solid, with no obvious loose or hollow concrete needing immediate repair.
- Inside, a fine crack below a window appeared to follow a plasterboard joint, and there were some long-standing gaps under the skirting boards.
I didn’t see evidence of significant structural movement in the areas I inspected. In my opinion, the cracking between the brickwork and the stumps was consistent with minor differential movement between the two materials, not a foundation problem.
Why Do Cracks Keep Coming Back After They’ve Been Repaired?
This is one of the most common frustrations with older buildings:
- Someone fills the crack with a rigid filler, sands it back and paints over it.
- The wall looks good for a while.
- The two sides move slightly, and the crack reappears.
The original repair wasn’t necessarily badly done. It just didn’t allow for the movement that caused the crack in the first place. Where the crack is at the junction between brickwork and a concrete stump, a flexible movement joint is usually a better answer than another rigid patch.
How Can These Cracks Be Repaired?
For this house, I recommended forming flexible joints between the brickwork and the concrete stumps. The repair is straightforward:
- Cut a neat vertical groove, nominally 10 mm wide, along the junction between the brickwork and the concrete.
- Clean the joint and remove any loose material.
- Install a closed-cell polyethylene backing rod.
- Apply a flexible polyurethane joint sealant, such as a suitable Sikaflex product, following the manufacturer’s requirements for joint width, depth and installation.
- Repaint the surrounding surfaces if needed.
The backing rod sets the depth and shape of the sealant and stops it bonding to the back of the joint. That lets the sealant stretch and compress as the two materials move.
The aim isn’t to stop all movement. It’s to accommodate small movements so the surface doesn’t keep cracking. A 10 mm joint suits minor cracking like this; where larger movement is expected, the joint width and sealant need to be designed for it.
These repairs weren’t urgent, so I suggested the owner do them progressively rather than all at once. This approach suits minor brickwork-to-stump cracking. A damaged or structurally inadequate stump needs a different assessment and repair.
What About Cracks in the Concrete Stumps Themselves?
A crack in a concrete stump is a different issue from a crack between the stump and the brickwork beside it. Stumps can crack because of shrinkage, corroding reinforcement, moisture-related deterioration or structural movement.
The things to check are:
- Is the concrete loose or hollow when tapped?
- Is reinforcement exposed or rusting?
- Is the stump significantly cracked, leaning or displaced?
At this house, the previously repaired stump still sounded solid. A downpipe discharged nearby, and long-term moisture may have contributed to the original deterioration. Rather than breaking out the old repair, I recommended improving the flashing, keeping water away from the stump and keeping an eye on it. If the concrete deteriorates further, a more substantial repair may become worthwhile.
How Do You Know If Your House Is Subsiding?
Not every crack means subsidence, but some patterns deserve a closer look. I’d be more concerned if I saw several of these together:
- Cracks that are noticeably widening or appearing in new places.
- Doors and windows that are getting harder to open or close.
- Significant changes in floor levels.
- Distorted or displaced structural framing.
- Cracked, leaning or deteriorating stumps.
- Erosion, undermining or drainage problems near the footings.
The QBCC’s guidance on subsidence makes a similar point: some cracking is a normal maintenance item, while wider cracks, bulging walls and sticking doors and windows should be investigated.
Crack width is useful, but it doesn’t tell the whole story. A narrow crack in an important structural element can matter more than a wider crack in a non-loadbearing wall. Location, pattern, history and the condition of the rest of the building all count. For more on reading crack patterns, see Cracks and Gaps.
Sometimes a floor level survey, crack monitoring or a foundation investigation is worthwhile. At this house, based on what I saw, none of them were warranted.
Can Poor Drainage Cause Cracking in a House?
Yes. Poor drainage and leaking pipes change the moisture in the soil around a building. Depending on the soil and the footings, that can contribute to foundation movement. Water can also cause local deterioration of building materials.
At this house, the flashing above the brick infill walls had been cut into several pieces and some sections were missing. I didn’t see water getting inside, but I recommended replacing the defective flashing so water is directed away from the building. Stopping water getting in is much cheaper than repairing the damage it causes later. Our article on drainage problems on sloping blocks covers this in more detail.
Do Cracks in an Older House Mean It Needs Underpinning?
No. Underpinning is a significant structural repair and shouldn’t be recommended just because a building has visible cracks. The first step is to work out what has cracked and why.
If the problem is minor differential movement between brick infill and concrete stumps, flexible joints may be all that’s needed. If the foundations have genuinely lost support or are moving excessively, further investigation and foundation repairs may be necessary. Those are very different situations, with very different costs.
When Should You Call a Structural Engineer About House Cracks?
If you’re worried about cracking, particularly around structural supports, get independent engineering advice before committing to expensive repairs. An inspection can tell you whether the cracking is cosmetic, caused by a local construction detail, or a sign of a broader structural problem.
Sometimes further investigation is needed. Sometimes the repair is simple. And sometimes the best advice is to leave it alone.
At this house, I didn’t recommend underpinning, a floor level survey or crack monitoring. The practical recommendations were flexible joints between the brickwork and the stumps, replacement of the defective flashing, and keeping an eye on the repaired stump.
Not every crack in an older Brisbane house means a serious foundation problem. What matters is understanding what has cracked, why, and whether anything actually needs to be done about it.
Concerned about cracks in your house? Send us photos and a short description and we’ll let you know whether an inspection is worthwhile.
Matt Cornell is a Registered Professional Engineer of Queensland (RPEQ 06598) and Director of Cornell Engineers. Cornell Engineers provides structural inspections and independent advice on existing homes and buildings throughout Brisbane and South East Queensland.