The Southern Highlands sits between 600 and 900 metres above sea level. In towns like Robertson, Burrawang and Bundanoon, overnight winter temperatures routinely drop below zero, and ground frosts are a weekly event from June through to late August. For pool owners, this isn’t just uncomfortable, it’s structurally destructive.
If your pool was installed when you moved into a rural-residential property or weekender decades ago and has sat largely unused through Highlands winters, there’s a good chance the cold has done far more damage than simple neglect. This guide explains exactly what freeze-thaw cycling does to the three main pool types, why the damage tends to be invisible until removal day, and why many Highlands homeowners ultimately decide that removal is the only sensible path forward.
Quick Answer (BLUF)
Repeated frost and freeze-thaw cycles crack concrete shells, delaminate fibreglass gelcoat, buckle steel above-ground frames and destroy plumbing fittings. In the Southern Highlands’ cold climate, an unused pool deteriorates roughly three to five times faster than the same pool in coastal Sydney. After several winters without active water circulation and chemical management, most pools are beyond economic repair, removal and landscaping is typically the better investment.
What “Freeze-Thaw Cycling” Actually Means for Pools
Freeze-thaw cycling happens when moisture in a porous material freezes overnight, expands by approximately 9%, then thaws during the day and contracts. Each cycle creates tiny internal stresses. Concrete is particularly vulnerable because it’s inherently porous at a microscopic level, water infiltrates hairline cracks, freezes, and forces those cracks wider. After 10 or 20 winters, what started as surface crazing can become full-thickness fractures.
The Highlands compounds this problem because the freeze-thaw cycles here are frequent and often severe. Robertson averages around 40 to 60 frost days per year and has recorded snow several times per decade. Bundanoon and Burrawang are similar. Even Bowral and Mittagong, which sit slightly lower, regularly see -3°C to -5°C on winter mornings.
Pools that are kept full, heated and chemically balanced through winter resist this damage because the circulating water doesn’t allow ice formation at the shell. But pools that are drained, half-empty or simply left without winterisation absorb ground moisture and experience the full destructive force of the freeze-thaw cycle.
Damage to Concrete Pools
Concrete (gunite or shotcrete) pools in the Highlands develop several characteristic failure modes over time:
Shell cracking. Hairline cracks form in the render layer first, then propagate through the structural shell. You’ll often see a map-cracking or spider-web pattern on the interior walls, this is the render failing. Water ingress behind the render accelerates the problem every winter.
Render delamination. The render coat bonds to the structural concrete, but freeze-thaw cycling breaks that bond. Large sections of render can lift and spall away from the pool wall, leaving rough aggregate exposed. Once delamination starts, it progresses quickly.
Deck heaving. The concrete surrounds around the pool are also affected. Clay soils in the Highlands expand and contract with moisture changes and frost. Pool decks crack, lift and become trip hazards, often within five to ten years of installation on poorly drained sites.
Plumbing failures. PVC plumbing in cold climates becomes brittle over time. The UV exposure at above-ground sections combined with repeated freezing makes pipework crack. Underground plumbing can also shift as saturated clay soils move.
After several harsh Highlands winters, the cost to repair a concrete pool typically runs to tens of thousands of dollars, often more than the pool’s original installation cost adjusted for inflation. See our concrete pool removal guide for what the removal process involves.
Damage to Fibreglass Pools
Fibreglass pools flex slightly, which makes them more frost-resistant than concrete in theory. In practice, the gelcoat, the smooth surface layer, is highly susceptible to osmotic blistering, which is accelerated by cold, wet conditions.
Osmotic blistering. Water molecules penetrate the gelcoat and react with the underlying laminate layers. In warm coastal climates this process is slow. In the Highlands’ cold, wet winters, the constant ground moisture and freeze-thaw cycling accelerates blister formation dramatically. Blisters appear as dome-shaped bubbles ranging from pea-sized to palm-sized across the shell.
Gelcoat crazing. Cold temperatures make the gelcoat brittle. Temperature differentials, a cold frosty morning followed by direct winter sun, create thermal stress that cracks the gelcoat surface. Once cracked, water ingress accelerates both the crazing and the osmotic blistering.
Shell lifting. A fibreglass shell that’s been drained in a high-water-table area can lift out of the ground as the soil saturates in winter. The buoyancy force of waterlogged clay or basalt soils can literally float a drained fibreglass shell. This is one of the most dramatic and expensive failure modes. Learn more about fibreglass pool removal and what’s involved in extracting a damaged shell.
Damage to Above-Ground Pools
Steel-framed above-ground pools face their own freeze-thaw problems. The steel frames rust at accelerated rates in wet Highlands winters, particularly if the pool is left full of untreated water that promotes algae and creates corrosive conditions. Frame connections corrode and fail, wall panels can buckle, and liners become brittle and crack in cold temperatures.
Basalt and Clay Soils Make It Worse
The Southern Highlands sits on a mix of basalt-derived soils (particularly around Robertson and Burrawang) and clay-heavy subsoils throughout Wingecarribee. Both soil types retain moisture rather than draining freely. This means the ground around and beneath your pool stays wet for longer after rain, maximising the freeze-thaw damage potential. Our guide to pool removal in clay soil covers the excavation challenges this creates.
Basalt soils also contain rock fragments at varying depths, when pool shells crack and water infiltrates, the surrounding basalt rubble can shift and create voids beneath the pool floor, leading to subsidence. The frost heave and backfill guide explains how this affects the fill-in process.
When Is a Pool Beyond Repair?
A useful rule of thumb: if the estimated repair cost exceeds 40-50% of the pool’s current replacement value, removal and landscaping almost always delivers better value. In the Highlands, given the climate damage multiplier and the limited swimming season (typically only four months per year at best), many homeowners find that a repaired pool still won’t justify the ongoing maintenance costs.
Signs that a pool has reached this point include: multiple full-thickness cracks in the shell, large-scale render delamination, significant blistering covering more than 20-30% of the fibreglass surface, frame structural failure in above-ground pools, or evidence of shell movement or lifting.
FAQs
Can I just drain my pool in winter to prevent frost damage?
Draining is actually more dangerous than keeping the pool full in cold climates. A drained concrete pool loses the hydrostatic pressure that counteracts soil movement, the shell can crack from external soil pressure. A drained fibreglass pool can lift entirely out of the ground if the water table rises. The correct approach for winterisation is to partially lower the water level, add winterising chemicals, shut down equipment and protect exposed plumbing. But many Highlands homeowners find this annual process unsustainable and choose removal instead.
Does my insurance cover frost damage to a pool?
Most home and contents policies exclude gradual deterioration, which is how insurers classify freeze-thaw damage. Unless there’s a sudden, identifiable event (such as a burst pipe causing immediate damage), frost damage to pool infrastructure is typically not a covered loss. Check your policy’s “gradual damage” or “wear and tear” exclusions.
How do I know if my pool has structural frost damage before getting a removal quote?
Look for map-cracking or spider-web cracking on interior walls, lifting or spalling render, blisters on fibreglass surfaces, cracked or heaved pool decking, or any visible gap between the pool coping and the surrounding ground level. A site inspection by a removal specialist will confirm the extent of the damage and inform the quote.
Does frost damage affect the cost of removal?
It can, particularly if the shell is fragmented or if unexpected voids have formed beneath the pool floor. However, structural damage generally makes the pool easier to demolish rather than harder, a cracked concrete shell breaks apart more readily. The main cost consideration is soil management: if voids have formed or if the soil has been significantly disturbed, additional compaction work may be needed. Contact Southern Highlands Pool Removals for a site-specific assessment.