Not every crack is the same
Cracks in a concrete pool fall into two broad groups, and the difference matters. Some are fine surface marks that are cosmetic. Others are structural, which means the shell itself is cracked and the repair has to deal with why it moved. A crack that gets filled and painted over without that diagnosis usually comes back.
This page covers cracks specifically. For the wider picture of how we diagnose and fix pool problems, see pool repairs.
Hairline and craze cracks
Craze cracking is a network of very fine lines across the surface, a bit like crazing on old pottery. Single hairline cracks are the same family. They’re usually in the finish itself, rather than the structure, and often come from the finish shrinking or ageing.
- Very fine, often branching lines across the surface
- No step or gap, where one side of the crack sits higher than the other
- No water loss linked to them
- Often worth watching more than rushing to fix
These are often dealt with as part of a resurface, because the old finish is coming off anyway. On a sound pool they may only need monitoring.
Structural cracks
Structural cracks go through the shell. They’re wider, they tend to run in a line, and they may show movement, with one side sitting differently from the other. A pool with a structural crack often loses water, and it’s worth checking quickly.
- A crack you can feel with a fingernail, or that’s visibly open
- A crack running through the floor, wall or at the junction of the two
- Cracks that keep coming back after being filled
- A pool losing water along with the cracking
If your pool is losing water, work out whether it’s a crack or something else. Our pool leak repair page explains how we track that down.
Why pool shells crack
Pool shells crack for a handful of reasons, and often more than one at once:
- Ground movement. The soil under and around the pool shifts over time.
- Reactive clay soils. Parts of western Sydney sit on clay that swells when wet and shrinks when dry, putting stress on the shell.
- Hydrostatic pressure. High groundwater pushes against an empty or low pool, which is why we check ground conditions before draining.
- Age and shrinkage. Older concrete and render develop cracks as they cure and weather.
- Tree roots and nearby loads. Large trees and heavy structures close to the pool can add pressure.
Knowing which one applies decides the repair. If the ground is still moving, the crack will move with it unless the cause is dealt with. Read about draining safely in our guide to hydrostatic valves.
How a crack is properly repaired
This is the difference between a repair and a cover-up. A crack that’s just filled and coated is still a crack underneath.
Open it up
The crack is cut open along its length, usually into a V or a channel, so the repair material has something to bond to and the full depth of the crack is exposed.
Clean and prime
Dust, loose material and old coating are removed so the repair bonds. Any exposed reinforcing steel is checked, because rusting steel can push the concrete apart.
Fill with the right material
The channel is filled with a pool-grade repair product suited to the crack, and built up in layers where needed. For cracks that may keep moving, a flexible product may be a better fit than a rigid one.
Make good the surface
Once the repair has cured, the surface is brought back to match. If the whole pool is getting a new finish, the repair sits underneath it as part of the resurface.
Straight advice: filling a crack and painting over it is the quick job that fails. We open it up, repair it properly and tell you honestly what we think caused it.
When an engineer is needed
Some cracks are beyond a surface repair. If a shell shows significant movement, an obviously bulging or displaced wall, cracks that keep widening or damage that suggests the ground itself is moving, the right step is a structural engineer’s assessment, not a patch. We’ll tell you plainly if we think your pool is in that category, and we won’t pretend a repair is enough when it isn’t.
Cracks and the finish on top
A crack repair is only half the job. The finish over it matters as well, because a brittle or thin coating will often show the crack again. If the surface is also tired, rough or stained, repairing the crack and then resurfacing the pool in one go is usually the cleaner outcome, and it avoids paying for the surface to be prepared twice.
It also helps to tell us when you first noticed the crack, whether it’s changed and whether the water level has been dropping. That history is useful when we work out whether the movement has stopped.
Book a crack inspection
We inspect first, work out whether the cracks are surface or structural, and quote the actual job in writing. Pool season opens in November and cracks are best sorted before then. Booking early gives you the widest choice of dates, whether you want to swim by November, Christmas or later in summer. We work across all of Greater Sydney.
