Owning a fibreglass swimming pool in Cape Town comes with great benefits — low maintenance, durability, and a smooth surface. However, one common issue many homeowners face over time is pool wall or floor bulging and cracking. These bulges may seem harmless at first, but they often signal underlying structural stress or groundwater pressure that needs attention.
At Pools Reno, we’ve seen how pool bulging and cracking can worsen if left untreated, especially in areas like Durbanville, Bellville, and Somerset West, where fluctuating water tables and clay soil are common. Let’s break down the causes, short-term and long-term fixes, and the best way to restore your pool.
What Causes Fibreglass Pool Shell Bulging and Cracking in Cape Town?
There are several reasons why a fibreglass pool shell might develop bulges, dents, or cracks. Understanding these causes helps prevent costly damage later.
1. Groundwater Pressure (Hydrostatic Pressure)
Cape Town’s winter rains can raise groundwater levels dramatically. When water builds up beneath the pool shell, it pushes upward, creating pressure that causes bulges in the floor or walls.
If your pool wasn’t installed with a proper sump or relief valve, this pressure has nowhere to escape, forcing the shell to flex outward.
2. Poor Drainage Around the Pool
In suburbs like Durbanville, Bellville, and Paarl, clay-rich soil retains water for long periods. Without proper drainage channels, the soil swells and puts stress on the pool walls. Over time, this constant pressure leads to deformation or bulging of the fibreglass surface.
3. Empty or Drained Pool During Rainy Season
Many homeowners make the mistake of draining their pools for cleaning or repairs during Cape Town’s wet months. When the surrounding ground becomes saturated, the empty shell can lift or deform under external pressure. Always consult a pool professional before draining your fibreglass pool.
4. Improper Installation or Poor Shell Support
If the pool shell was installed without even backfilling or compacting the soil properly, small gaps can form underneath. These gaps allow the shell to flex and weaken under pressure, creating bulges or even cracks at stress points.
5. Temperature Fluctuations and Ageing
Cape Town’s strong UV rays and seasonal temperature changes also affect fibreglass pools. Over time, heat expands the material while cold contracts it, causing gradual warping or delamination in older pools.
Short-Term Fixes for Pool Wall or Floor Bulging
While short-term fixes can improve the pool’s appearance temporarily, they won’t stop the root cause. These are only suitable when the structural damage is minor.
- Releasing Groundwater Pressure:
Using a sump pipe or hydrostatic valve, we can relieve water pressure underneath the pool. - Draining and Re-leveling:
For small bulges, our team may partially drain the pool and recompact the soil beneath it. - Surface Sanding and Patching:
Small cracks or raised areas can be sanded down and patched using a fibreglass resin mix, which seals the area until a full relining is done.
However, these are temporary solutions. If you see cracks or large deformations, it’s time for a permanent fix.
Long-Term and Permanent Repair Solutions
When bulging or cracks are more severe, professional fibreglass relining is the best way to restore your pool’s strength and appearance.
1. Full Fibreglass Relining
This process involves grinding down the damaged surface, repairing structural weak points, and applying multiple new fibreglass and resin layers. A fresh gel coat is then added for protection and a glossy finish.
At Pools Reno, we use high-quality materials designed to withstand Cape Town’s weather and groundwater conditions.
2. Installing a Sump or Hydrostatic Relief Valve
This is crucial for pools affected by high water tables. The valve allows trapped groundwater to escape, preventing future pressure buildup and bulging.
3. Soil Drainage Improvement
If poor drainage is the cause, our team can design a groundwater management system using perforated pipes or gravel beds around the pool.
This ensures excess water flows away instead of pushing against your pool structure.
4. Reinforcing with Structural Supports
In extreme cases, additional structural braces or shell supports can be installed to stabilise the pool walls before relining.
Best Way to Repair Bulging and Cracking in Fibreglass Pools
The best repair option depends on the extent of the damage and the surrounding soil conditions.
For Cape Town homeowners, the ideal long-term solution is a complete fibreglass relining, combined with a hydrostatic valve installation.
This not only removes existing bulges but also prevents future pressure-related issues.
At Pools Reno, we’ve successfully repaired fibreglass pools in Stellenbosch, Somerset West, and Table View, where soil movement and groundwater levels often cause structural deformation.
Our process ensures your pool looks new again — smooth, watertight, and perfectly level.
Why Cape Town Pools Are Prone to Bulging
Cape Town’s geography makes fibreglass pool maintenance unique. The high clay content, seasonal rainfall, and shifting groundwater all combine to create challenging conditions for pool shells.
This is why regular inspections and groundwater checks are crucial for keeping your pool stable and safe.
Final Thoughts
A bulging fibreglass pool isn’t just a cosmetic issue — it’s a sign of stress within your pool’s structure. Acting quickly can save you thousands in future repairs.
Whether it’s a small floor bulge or visible wall deformation, Pools Reno provides expert fibreglass pool inspections, repairs, and full relining services throughout Cape Town and the Western Cape.
Frequently Asked Questions
Q1: Can a bulging fibreglass pool be repaired without draining it?
Minor bulges can sometimes be stabilised without draining, but in most cases, partial draining is needed to relieve pressure safely.
Q2: How much does fibreglass relining cost in Cape Town?
Costs vary depending on pool size and condition, but most full relines range from R25,000 to R55,000. Always request a site visit for an accurate quote.
Q3: Can groundwater cause pool cracks?
Yes. Continuous groundwater pressure can weaken the fibreglass shell, leading to stress cracks and bulging.
Q4: How do I prevent my pool from bulging again?
Install a sump drain or hydrostatic valve, improve site drainage, and avoid draining your pool during the rainy season.
📍 Related Services We Provide
- Fibreglass Pool Relining in Cape Town
- Marbelite Pool Resurfacing Services
- Leak Detection and Pool Crack Repairs
