Can a Cement Mortar Be Used for Levelling Swimming Pool Walls and Floors?

When constructing a swimming pool, one of the common questions is whether a cementitious mortar can be used as a levelling layer beneath the waterproofing membrane and tile installation system. The answer is yes, provided the mortar is specifically designed for the application and demonstrates the necessary performance characteristics through standardized testing.

It is important to understand that a levelling mortar is not intended to act as the waterproofing layer. Its primary function is to provide a sound, smooth, dimensionally stable, and durable substrate for the subsequent waterproofing and tile installation system. Therefore, acceptance of a cementitious mortar should be based on its engineering performance rather than solely on its compressive strength.

What Performance Is Required Cement Mortar Be Used for Levelling Swimming Pool Walls and Floors?

A levelling mortar intended for swimming pool applications should possess the following properties:

1. High compressive strength to withstand service loads. ASTM C109/C109M or EN 12190 - : 25 MPa at 28 days
2. Excellent bond strength to the concrete substrate. ASTM D4541 or EN 1542 - 1.0 MPa
3. Low water absorption and permeability. ASTM C642 - ≤ 6–8% by mass.
4. Good dimensional stability with minimal shrinkage. Drying Shrinkage - ASTM C157 - ≤ 0.10% (1000 microstrain).
5. Adequate flexural and tensile strength to resist cracking. ASTM C348) – evaluates crack resistance.
6. Durability under continuous water immersion. An immersion period of 28 days - No softening - No cracking - No delamination - No reduction in bond strength - No surface deterioration after prolonged immersion
7. Compatibility with the specified waterproofing membrane and tile adhesive. Pull-off strength as a system - BS EN 14891 - 0.5 MPa
8. Application thickness: As screed- min 15 - 50 mm, up to 100 with mesh. As plaster - min 8 - 15mm, up to 30mm in 2 pass.
9. Bonding to substrate - with bonding agent - min 1 MPa pull-off strength

Pool System:

A properly designed swimming pool does not rely on the levelling mortar for waterproofing. Instead, the complete system typically consists of:

1. Reinforced concrete (RCC) shell.
2. Cementitious levelling mortar or screed.
3. Waterproofing membrane.
4. Tile adhesive.
5. Ceramic, porcelain, or glass mosaic tiles.
6. Tile joint Grout.

Each layer performs a specific function, and the overall durability of the swimming pool depends on the compatibility and performance of the entire system.

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