If you've noticed a hairline crack in your Plungie, or you've come across the topic online and want to understand it before you invest, this article covers what you actually need to know. Hairline cracks in concrete pools are one of the most misunderstood aspects of pool ownership. Some are a normal characteristic of concrete and expected across every concrete pool ever built. A small number indicate a genuine issue that warranty should address. Knowing which is which is the fastest way to move from worry to action.
Below, we walk through what causes hairline cracks, how to tell a cosmetic crack from a structural one, exactly what a Plungie's warranty covers, what to do if you spot a crack in your own pool, and how Plungie's manufacturing process has continued to develop.
Yes. Every concrete pool, whether it's a traditional shotcrete build, a poured-in-place gunite pool, or a precast pool like a Plungie, has the potential to develop hairline cracks over its lifetime. This is a well-documented characteristic of concrete as a material, not a manufacturing fault or a defect specific to any one pool company.
Standard construction warranty language across the residential building industry reflects this. Warranty documents for concrete foundations, driveways, patios, and pool shells routinely state that hairline cracks caused by the natural expansion and contraction of concrete do not affect structural integrity and are not covered by warranty. This is the industry norm, not a Plungie-specific position, and it applies to concrete construction in general.
What matters isn't whether a hairline crack exists. It's what type of crack it is, where it sits, and whether it changes over time.
Concrete is a mix of cement, water, aggregate, and reinforcing steel. Once poured (or in Plungie's case, cast in a factory), it goes through a curing process where the material sets, gains strength, and settles into its final structural state. That process, and the environmental conditions the pool sits in afterward, cause a small amount of movement. Sometimes that movement shows up as a hairline crack.
As concrete cures, it loses moisture and shrinks slightly. This is called drying shrinkage, and it's the single most common cause of hairline cracks in any concrete surface. In a Plungie, the curing process happens in the Brisbane factory under controlled temperature and humidity conditions, which reduces (but doesn't eliminate) shrinkage cracking compared to on-site pours.
Concrete expands when it heats and contracts when it cools. On a hot Australian summer day followed by a cool night, the shell of a pool moves millimetre-scale amounts as the temperature changes. Over time, that repeated movement can produce hairline surface cracks. This is why cracks are more common in concrete pools in extreme climates than in mild ones.
The ground your pool sits in isn't static. Reactive clay soils common across South East Queensland, Northern NSW, and parts of Victoria and SA swell when wet and shrink when dry, moving the surrounding earth up and down through the seasons. Sandy soils compact and settle over time. Well-engineered pools handle this movement, but small hairline cracks in the shell can occur where the ground movement is greatest.
Groundwater exerts significant upward pressure on any inground pool. Heavy rainfall, high water tables, or poor site drainage can push the water table up against the base of the shell. Every Plungie is supplied with a hydrostatic valve that releases this pressure into the pool, but sites with severe drainage issues can put ongoing stress on the shell.
This is the distinction that matters most, and it's the one homeowners find hardest to make on their own.
A cosmetic hairline crack has the following characteristics:
Cosmetic hairline cracks are not a warranty issue and don't affect the pool's structural performance or lifespan. In many cases, they're only visible up close or in certain light. If you're not sure whether what you're seeing is cosmetic, photograph it against a coin or ruler and monitor it over a few weeks to see if it changes.
A structural crack looks and behaves differently. Signs that a crack may be structural include:
Structural cracks are a warranty matter. If any of these apply to your Plungie, stop monitoring and get in touch immediately.
Traditional gunite and shotcrete pools are built on-site over 6 to 16 weeks, in whatever weather conditions happen to exist at the time of the pour. Concrete cures over the following 28 days in the open. Surface preparation, humidity, ambient temperature, the sequence of the trades, and installer technique all introduce variables that affect the finished shell.
Plungie is different. Every shell is cast in a controlled environment at our NATA-accredited Brisbane manufacturing facility, on a schedule that doesn't depend on weather, with concrete mixed to a tested specification. That reduces the variables that produce cracking in on-site pours. It doesn't eliminate cracking altogether, because concrete is still concrete, but it produces a more consistent finished shell than a poured on-site pool.
For more detail on how Plungie is manufactured, see our article on what ecoFinish is and how it's applied at our Brisbane facility.
Every Plungie sold in Australia comes with a three-tier warranty:
Full details are on the Plungie warranty page.
Manufacturing defects that affect the structural integrity of the pool shell. That includes structural cracks caused by faults in the manufacturing process, adhesion failures between structural layers, and shell failures that aren't caused by external factors.
Manufacturing defects in the ecoFinish application. That includes adhesion failures, blistering, and finish integrity issues that aren't caused by external factors like chemical imbalance or unauthorised cleaning products.
Consistent with industry-standard concrete warranty terms, the following are not covered:
Australian Consumer Law provides consumer guarantees that operate independently of any manufacturer's warranty. Under the ACL, products must be of acceptable quality, fit for purpose, and match their description. These consumer guarantees apply to your Plungie regardless of the stated warranty period, though the specific remedies available depend on the nature and timing of the fault. Legal advice on ACL rights is best sought from a qualified professional if a warranty claim is disputed.
The process is straightforward, and we'd rather hear from you early than late.
If the crack is cosmetic, we'll tell you and explain how to monitor it over time. If it's a warranty matter, we'll coordinate the assessment and repair through our network. If it's chemistry-related or otherwise not covered, we'll give you clear guidance on how to address it.
Plungie has manufactured precast concrete pools in Australia since 2018. Like any manufactured product, the process has developed considerably since those first installations. We've taken every learning seriously along the way, and the quality controls below are the result of that ongoing commitment to refining how we build.
Three specific quality controls have been added over that period, and the Plungie Quality page has the full picture:
Small cosmetic hairline cracks can occur in any concrete pool as a natural characteristic of the material. They're not typically a warranty issue on their own, but they should be photographed and monitored. Structural cracks are a different matter and should be reported to Plungie for assessment immediately.
Cosmetic hairline cracks in the ecoFinish surface don't typically cause leaks because the ecoFinish membrane is fully sealed and the underlying concrete shell is intact. Structural cracks that extend through the shell can cause water loss, and any suspected leak should be reported to Plungie immediately.
The best approach is to photograph the crack, note when you first saw it, and contact Plungie through the warranty inquiry form. Our warranty team assesses each claim individually based on the photos, the pool's production record, and any site information the installer has on file.
We don't recommend DIY repairs on any crack in a concrete pool. If the crack is cosmetic, it typically doesn't need repair. If it's structural, DIY repairs can compromise the shell and complicate any subsequent warranty assessment. Contact Plungie first before doing anything to a visible crack.
Every type of concrete pool has the potential to develop hairline cracks over its lifetime because of the way concrete cures and responds to temperature and ground movement. Traditional shotcrete and gunite pools tend to develop more cracks over time than precast pools because they cure in less controlled conditions. A Plungie is cast in a controlled factory environment, which reduces (but doesn't eliminate) the potential for cracking.
If you're an existing Plungie owner and you're not sure whether what you're seeing is cosmetic or structural, the fastest way to find out is to send us the photos and let us assess. If you're considering a Plungie and want to talk through concrete performance in more detail, we're happy to walk you through it directly.