Every Wagga Wagga homeowner faces wall cracks eventually. Reactive clay soil, extreme summer heat, and decades of seasonal movement mean cracking is a fact of life in the Riverina. The question most homeowners ask is: can I fix this myself? Sometimes yes. Often no. The difference matters, because DIY repairs on the wrong type of crack can mask a structural problem, lead to water damage, and cost significantly more to fix properly later. For a guide to identifying which cracks are serious, see our article on when wall cracks are cause for concern.
Quick answer (BLUF)
Hairline cosmetic cracks in plaster or render, stable, under 1 mm wide, not associated with any structural movement, can be safely filled by a competent homeowner. Cracks in brickwork wider than 3 mm, diagonal or stepped cracks associated with door or window frames, cracks that have grown over time, or any crack where you are uncertain of the cause should be assessed by a professional before any repair is attempted.
The fundamental DIY rule: diagnose before you fix
The biggest mistake DIY foundation crack repairs make is cosmetic filling without any diagnosis. If you fill a crack that is still actively moving, the filler will re-crack, usually sooner than you expect. Worse, if the crack is an indicator of progressive foundation movement and you simply paint over it, you lose your only visible warning sign.
Before attempting any crack repair, ask yourself:
- Is the crack stable? Has it changed size, shape, or length in the past twelve months? If you cannot answer this with confidence, monitor it for at least one full seasonal cycle (one summer and one winter) before filling.
- What is the likely cause? A hairline crack in plaster along a ceiling cornice has a very different cause from a 4 mm diagonal crack in brickwork above a door frame. If you are not sure what caused a crack, do not fill it until you find out.
- Is there associated movement? Do nearby doors or windows stick? Is there a corresponding crack on the opposite side of the wall? Does the floor slope toward the crack? Associated movement strongly suggests a foundation cause that needs professional investigation.
What you can safely DIY
Hairline plaster and render cracks
Hairline cracks (under 1 mm) in internal plaster or external render, with no associated structural movement, are suitable for DIY repair. These are almost always cosmetic, the result of normal thermal movement, plaster shrinkage, or very minor seasonal flexing.
Materials: Acrylic gap filler or interior flexible crack filler for internal plaster. Exterior flexible render patch or acrylic gap filler for rendered external walls.
Method: Clean out the crack with a narrow tool (old screwdriver or similar) to remove loose material. Apply the filler with a flexible spatula or your finger, slightly overfilling. Once dry, sand flush. Prime and repaint. For external render, apply a render patch matched to the existing texture.
Mortar joint repointing in stable brickwork
Small areas of crumbled or missing mortar in stable brickwork, where there is no movement and the existing mortar simply aged out, can be repointed as a DIY task.
Materials: Bagged mortar mix matched to the existing mortar colour and type. Note: using too strong a mortar (too much cement) in older brickwork can cause new cracks adjacent to the repair.
Method: Rake out the damaged mortar to at least 15 mm depth. Wet the joint. Pack in new mortar, striking to match the existing profile. Keep the repair damp for 24-48 hours to allow proper curing.
Expansion joint sealing
If a crack runs along what appears to be an old expansion joint (typically a vertical crack in brickwork at regular intervals), and the crack is simply the joint that has lost its sealant, this can be refilled with a polyurethane sealant or backing rod plus sealant system.
What you should NOT attempt as DIY
Cracks wider than 3 mm in brickwork
These indicate significant movement, not cosmetic imperfection. The mortar in a wide crack has typically been displaced, not just cracked, and simply packing it back in will not restore structural continuity. More importantly, a crack of this width in brickwork has a cause, and that cause needs to be diagnosed by a foundation inspection before any repair.
Diagonal cracks above door and window openings
These are a classic indicator of differential foundation settlement. Filling them without addressing the foundation movement is pointless, they will re-open, often within one seasonal cycle. The correct approach is: get the foundation assessed, address any active movement, then repair the cracks once stability is confirmed.
Stepped cracks tracking across multiple courses
Stepped cracking indicates shear movement, horizontal sliding between sections of the wall. This is a structural concern, not a cosmetic one, and requires professional assessment.
Any crack that is growing
If you have measured a crack and it is wider this year than last year, even by 1-2 mm, do not fill it. The crack is telling you something about ongoing foundation movement. Get it assessed.
Concrete slab cracks
Cracks in concrete slabs may indicate slab structural failure, not just cosmetic distress. Attempting to fill slab cracks without understanding whether the slab has fractured through its depth, whether reinforcement has been compromised, or whether the underlying soil movement is ongoing, can mask a serious problem.
The cost comparison
A professional foundation crack repair for a correctly diagnosed stable crack might cost $200 to $800 depending on the extent. A DIY repair of the wrong crack, masking ongoing movement, can ultimately result in far greater structural damage and a bill for underpinning or slab replacement that runs into tens of thousands of dollars. The investment in a foundation inspection before attempting any repair is almost always worthwhile.
FAQs
Can I use foam filler in a crack to stop water getting in?
Expanding foam is not appropriate for masonry crack filling. It does not adhere properly to brickwork or concrete, cannot be adequately painted, and has no structural value. Use flexible exterior-grade sealant for temporary water exclusion while you arrange a proper assessment.
How do I know if a crack in my Wagga brick home is cosmetic or structural?
The combination of crack width, pattern, location, and whether associated movement is present (sticking doors, floor slope, multiple cracks in the same area) tells you more than any single factor. Our guide on when cracks are cause for worry walks through the assessment process. When in doubt, book a foundation inspection.
My painter says the cracks are nothing to worry about, should I trust their opinion?
Painters are not structural engineers and are not trained to assess foundation conditions. A painter correctly observing that cracks appear cosmetic is useful input, but not a substitute for a structural assessment when there are multiple or widening cracks. Foundation problems caught early are far less expensive than those left until they are unavoidable.