Pool Shell Crack Repair

Most fibreglass pool shell cracks are cosmetic and easily repaired with sanding, resin, and gelcoat — but structural cracks caused by soil movement or poor installation need professional repair. Catching small cracks early prevents water intrusion, delamination, and costly long-term damage.

Even the toughest fibreglass pool shells can show a few battle scars over time (like that one time your dumbass mate thought it’d be a good idea to ride a bike straight into the pool). A small crack along a step, a hairline mark near a return jet — it’s not the end of the world, but it is something that deserves attention.

Fibreglass is strong, flexible, and resilient — but like any engineered material, it responds to the world around it: ground movement, shifting water levels, or years of chemical imbalance. The good news? Most cracks can be repaired effectively if you act early and use the right approach.

Here’s how professionals look at pool shell cracks — what they mean, how to fix them, and when it’s time to bring in the experts.

Key Takeaways

• Cracks happen — and not all are serious. Many are surface-level gelcoat cracks caused by ground movement, chemical imbalance, or pressure shifts.
• Identify severity first. Hairline cracks can be patched DIY; wide, leaking, or flexible cracks signal structural issues that need expert repair.
• DIY repair basics: Drain below the crack, sand, clean, apply resin and gelcoat, then polish for a seamless finish.
• Structural cracks need more. Professionals may grind, rebuild layers, or inject resin to restore full strength.
• After repair: Always rebalance water chemistry, refill slowly, and monitor for leaks or spreading.
• Prevention matters: Keep water levels stable, maintain pH and alkalinity, and inspect annually for small cracks before they worsen.
• Expert insight: Fibreglass pools are tough but not invincible — consistent care and early attention make cracks a small fix, not a big problem.

Why Cracks Happen in Fibreglass Pool Shells

A crack doesn’t necessarily mean your pool is failing. Most are surface-level issues, not structural ones. The causes usually fall into these categories:

• Ground movement: Even slight soil shifts can flex a pool shell. Fibreglass is designed to bend slightly — but sharp movements can still stress the laminate.
• Poor backfilling: If the shell wasn’t evenly supported during installation, hollow spots can form behind it, leading to flexing and minor cracking over time.
• Thermal and water pressure changes: Rapid temperature swings or incorrect water levels (especially draining) can cause internal stress.
• Chemical imbalance: Over-chlorination and low pH can weaken the gelcoat surface, making it more prone to hairline cracks.

💡Expert insight: The majority of cracks are cosmetic — often just in the gelcoat. The structure underneath is usually fine. The danger is ignoring them until water seeps through.

If you’re here because you’ve spotted early signs of wear, you might also find our guide on pool shell maintenance tips helpful — it covers how to prevent these issues from developing in the first place.

Assessing the Severity of the Crack

Before you reach for any tools, figure out what you’re dealing with.

💡Pro tip: Dry the area and tap lightly with your knuckle — a hollow sound means delamination or backfill voids. That’s when DIY ends and structural repair begins.

Pool Shell Crack Repair: Tools and Materials Needed

For small surface repairs, you don’t need a full workshop.

You’ll need:

• Fine-grit sandpaper (240–400 grit)
• Acetone or fibreglass cleaner
• Fibreglass repair kit (resin, catalyst, mat, and gelcoat)
• Mixing sticks and disposable brushes
• Polishing compound and microfiber cloth
• Safety gloves, goggles, and mask

💡Expert tip: Always match the gelcoat colour to your pool’s original shade.

How to Repair Minor Fibreglass Cracks

This process works for hairline or cosmetic surface cracks — the kind you notice but can’t feel underfoot.

1. Drain the water below the damaged area. Dry it completely.
2. Sand the crack gently until smooth, removing loose or chalky gelcoat.
3. Clean the area with acetone to remove oils and debris.
4. Mix resin and catalyst according to instructions.
5. Apply a thin layer of resin over the crack. For deeper spots, add a small piece of fibreglass mat.
6. Let it cure fully (follow product time — usually 12–24 hours).
7. Sand again lightly, then apply gelcoat. Smooth evenly and let cure.
8. Polish and blend the repaired area with compound for a seamless finish.

💡Pro insight: Less is more. Thin layers cure stronger than thick ones, and a steady hand beats rushing with too much material.

Repairing Structural Cracks

Structural cracks — the kind that leak or expose fibreglass fibres — are a different story.

These typically indicate underlying stress or movement and require a full rebuild of the affected area:

• Drain and inspect. Identify whether the shell has shifted or if the backfill has collapsed.
• Grind out the damaged section down to solid laminate, creating a V-shaped groove.
• Layer new fibreglass mat and resin to rebuild strength, curing each layer completely.
• Apply barrier coat and gelcoat to reseal and match the finish.
• Test water level stability before refilling fully.

💡Expert warning: If the pool continues to lose water or if cracks reappear, it’s likely a structural shift below the shell — not just a surface issue. At that point, call in a fibreglass technician or installer to assess the foundation.

If the water level keeps dropping even after repairing a visible crack, the problem may be elsewhere. You can follow our pool shell leak detection guide to confirm whether the leak is coming from plumbing, fittings, or the shell itself.

After the Repair: Testing and Monitoring

Once repairs are complete:

• Rebalance your water chemistry. Over-chlorinated water can attack fresh gelcoat.
• Refill slowly. Monitor the waterline for 24–48 hours to confirm no leaks.
• Watch for recurrence. If the crack reopens or spreads, the problem lies deeper (backfill or soil movement).

💡Pro insight: Keep photos of the repair area before and after. It helps track whether the issue is truly fixed or if there’s ongoing stress.

When to Call a Professional

You should always call a pool technician if:

• The crack leaks water or feels soft around the edges.
• You notice multiple cracks forming in the same area.
• You suspect ground movement or shifting.
• You’re unsure whether it’s structural or cosmetic.

Professional repair teams use vacuum bonding and resin injection systems that restore structural strength without cutting the shell — something DIY kits can’t replicate.

Prevention and Long-Term Care

The best crack repair is prevention.

• Keep water levels stable. Don’t drain without guidance — empty shells can shift or lift.
• Balance chemicals. pH and alkalinity out of range are the silent destroyers of gelcoat.
• Inspect annually. Hairline cracks caught early are easy fixes; left alone, they spread.
• Check backfill stability. If you ever see dips or hollow spots around your pool, get them checked before the shell flexes.

💡Expert tip: Think of your fibreglass shell like a car’s paintwork — resilient but not indestructible. Gentle, regular care keeps it looking and performing its best.

Pool Shell Crack Repair: Handle It Correctly

A crack doesn’t mean failure — it means your pool is asking for attention. Fibreglass is forgiving and easy to repair if handled correctly.

For small cosmetic issues, a DIY fix can work beautifully. But for anything deeper, the smartest move is calling in a professional before small stress becomes major damage.

Need help or advice on your fibreglass pool repair? Pool Tools can guide you through identifying, assessing, and repairing pool shell cracks — or connect you with trusted technicians across Australia.