Concrete naturally moves: it expands in summer, contracts in winter, and develops shrinkage micro-cracks within the first few years. These micro-cracks, often invisible to the naked eye, are enough to let several liters of water seep through per hour.
Weak point number one: cold joints
When the floor slab and walls of a concrete pool are poured at different times, the junction between the two, the "cold joint", becomes a structural weak point. This is where the vast majority of leaks observed on concrete pools originate, far more than on the body of the walls themselves.
What to require before work starts
- A single pour, floor slab and walls poured the same day by concrete pump, with no cold joint.
- Certified XD2 concrete, dosed at 350 kg of cement/m³, from a concrete plant, not mixed on site.
- Verified rebar, TOR steel bars properly positioned and covered, not simply laid at the bottom of the formwork.
- Respected curing time, 28 days before full strength, without rushing to fill the pool.
What if the damage is already done?
Once a leak has set into a concrete pool, repair is tricky: groundwater often finds another path as soon as the visible crack is sealed. Inactive cracks are treated with epoxy resin, active cracks (often around the fittings) with flexible silicone sealant, but neither solution recreates the one-piece structure that a correct pour would have achieved from the start.
A fiberglass shell structurally eliminates this risk: it is one piece from the moment it's manufactured in the workshop, with no floor-to-wall junction. See our full concrete vs fiberglass comparison.