Technical Guide: Waterproofing a Concrete Swimming Pool

Solutions & Applications · Cementitious Waterproofing Products

A swimming pool is a tank that is subjected to pressure from both sides: when full, the water exerts pressure from the inside; when empty, on ground with water, the pressure comes from the outside. Above the waterproofing, there is almost always a tile or mosaic, and underneath there is concrete which will eventually crack. The right cementitious waterproofing material is not chosen based on the brand but on three factors: depth, cracks and ground water.

Three questions before selecting the material

Question	Why it matters	What guides
How deep is the swimming pool?	Each waterproofing product specifies a maximum water column. Elasticity is measured in terms of water column: elastic materials can withstand less	Up to 5 m: flexible; deeper than that: rigid or crystalline
Will the building envelope shift or crack?	Thermal expansion and contraction, as well as settlement, cause hairline cracks which rigid materials cannot accommodate	Elastic material that bridges cracks ≥ 0.5 mm
Is there water in the ground around it?	When the swimming pool empties, the pressure reverses and pushes the waterproofing from behind	Material with declared strength on the negative side

Which waterproofing product for which swimming pool?

Product	Type	Cracks	Water column · side	Tiles
CERESIT CR 166	Two-component elastomer	Bridging ≥ 0.5 mm	Up to 5 m · positive & negative	After 3 days
VANDEX CEMELAST 100	Two-component elastomer	Bridges gaps of up to 0.5 mm	Pressurised water, 3 mm thick	Suitable for use under tiles
CERESIT CR 65	Rigid single-component	Does not bridge	Up to 10 m · positive & negative	After 7 days
CERESIT CR 90	Crystallic	Seals capillary gaps up to 0.4 mm	Up to 15 m positive · 5 m negative	Do not fill with water until at least 5 days have passed
VANDEX SUPER	Penetrating crystalline	Seals pores and small cracks	Negative pressure up to 14 bar	Within the concrete, not as a separate layer

For a standard domestic swimming pool, with a depth of up to approximately 2.5 m and a tiled or mosaic finish, the first choice is a flexible system: CERESIT CR 166 or VANDEX CEMELAST 100. On ground with a water table, crystalline concrete waterproofing applied from within is applied beneath the elastic layer.

New swimming pool: waterproofing starts with the concrete

In new builds, the building envelope is designed to be airtight and watertight before the first layer of waterproofing is applied:

• Mass waterproofing — SINTOMIX SM N renders concrete impervious to water penetration and is chloride-free, making it suitable for reinforced concrete. Tanks fall within its scope of application.
• Floor-to-wall joint — where the concrete pour is interrupted, water finds a path. This is sealed during concreting using ESHAHYDROBENT or PVC Waterstop.
• Penetrations — skimmers, outlets, light fittings: these should be installed before concreting and, where possible, should not be cut out later using a core drill.

Step-by-step application

1. Sound substrate. Removal of loose material, formwork oil and cement screed. Hollows and delaminations are repaired using SINTOCRETE (R4) or SINTOCRETE Basic (R3) fibre-reinforced repair mortar in accordance with EN 1504-3.
2. Active leaks and corners. Leaking areas are sealed with VANDEX PLUG, which sets in approximately 30 seconds. At the junction between the floor and the wall, a channel is formed using VANDEX UNIMORTAR.
3. Wetting. The substrate should be damp, not soaked — with no standing water.
4. First coat and tape. The first coat of CR 166 is applied with a brush, in generous quantities. Whilst it is still wet, the Ceresit CL 152 tape is pressed into it at all corners, edges and around penetrations.
5. Second layer, laid crosswise. After approximately 3 hours, lay diagonally to the first layer, encasing the tape. Each layer up to 1.5 mm; for waterproofing under pressure, the total thickness is 2.5 mm (~4.3 kg/m²). With CEMELAST 100: 3 mm (~5.1 kg/m²), up to 4 kg/m² per pass.
6. Protection. Three days’ protection from the sun, which dries things out quickly, frost and rain.
7. Water-tightness test. Before tiling, the swimming pool is filled gradually and the water level is monitored for 48–72 hours. With CR 90 crystalline waterproofing, the pool is not filled until 5 days have elapsed.
8. Tiling. Class C2TE S1 adhesive — CERESIT CM 17 for tiles or CERESIT CM 25 for glass mosaic — applied in two coats (to the substrate and the back of the tile), so that coverage is at least 90 per cent.

Mistakes that cost

Incorrect	Consistency
Elastic waterproofing membrane in a swimming pool deeper than the specified depth	The layer performs beyond its limits; in deep pools, a material with a greater column depth is selected
Rigid waterproofing membrane in a crack-bridging shell	The crack in the concrete extends into the waterproofing
Corners without tape	The first contraction opens up the corner — the most common point of leakage
One thick layer instead of two cross-laid layers	Shrinkage cracks and unsealed pores
Tiles without waterproofing tests	The leak is identified once the cladding has been sealed
General-purpose adhesive or bathroom grout for underwater use	Delamination and joints that are being washed away

Swimming Pool Waterproofing

Preparation & Repair

New Cladding & Lining

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