Concrete pools are sealed using a waterproof membrane applied to the cured shell before the interior finish goes on. The dense shotcrete shell (4,000+ PSI) provides the base resistance. A flexible cement-based or polyurea membrane is then applied in two coats to seal hairline cracks and prevent water ingress.
How waterproofing actually works on a concrete pool
Concrete is not naturally waterproof. It’s porous, and without proper sealing, water will seep through over time — damaging the shell from the inside out and letting groundwater push back in from outside. Waterproofing is the step that makes a concrete pool watertight for decades.
The three-layer system:
Layer 1 — The concrete shell itself. Properly applied shotcrete at 4,000+ PSI (or 5,000+ PSI for saltwater pools) is dense enough to be substantially water-resistant. The quality of this layer is set at the time of the build — it’s why choosing a builder who uses commercial-grade concrete and equipment matters.
Layer 2 — The waterproof membrane. After the shell cures, a flexible waterproofing membrane is applied to the entire surface. Common systems include:
- Cement-based flexible membranes (e.g., Maxseal Flex) — applied in two coats, good for tiled pools
- Polyurea spray membranes — seamless, fast-curing, flexible, excellent for raised pools
- Crystalline waterproofing — penetrates the concrete and forms crystals in the pores
The membrane does two things: seals against the water inside the pool, and protects against groundwater pressure from outside. Both directions matter.
Layer 3 — The interior finish, Pebblecrete, tiles, or glass bead, applied over the membrane, adds another layer of protection while providing the final visible surface. This finish is what you see and touch — and it’s what eventually needs resurfacing as it wears.
What happens if waterproofing is done poorly?
- Water seeps through the shell, causing efflorescence (white mineral deposits on the outside of the pool wall)
- Groundwater pushes through, lifting tiles or cracking the finish
- Steel reinforcement rusts from moisture contact, causing concrete to crack from the inside
- Ongoing chemical leakage into the surrounding soil
Waterproofing done properly during the build is far cheaper than fixing a pool that wasn’t done right. It’s one of the areas where cutting costs at the construction stage creates expensive problems years later.
Disclaimer: Waterproofing methods and membrane products vary by builder. Cascade Pools uses high-quality commercial membrane systems on every build. All pools are constructed and waterproofed to Australian Standards. If you’re concerned about an existing pool’s waterproofing integrity, contact us for an assessment.