What Material is Best for Waterproofing Pools?

Firefighting water storage pools, swimming pools, garden landscape pools, surf pools, and other such areas require a long-term water fill. Poor waterproofing leading to leakage is not just troublesome, but also costly to repair. Hence, the waterproofing demands for pools are stringent, and selecting the right waterproofing coating is of utmost importance.

The various coatings used for pools must satisfy four critical functional requirements: adhesion, resistance to cleaning agents, crack resistance, and environmental friendliness.

1. The waterproof coating must exhibit good water resistance and weatherability to ensure that the waterproof layer does not peel or flake off under long-term water immersion.
2. For water storage pools like swimming pools, the selected waterproof coating must withstand underlying shrinkage or settling, thus requiring excellent extensibility.
3. The bond with the base layer must be robust and secure to prevent peeling or blistering in high humidity or soaked conditions.
4. The best choice in eco-friendliness, especially for drinking water or fish ponds, is green, non-toxic waterproofing products. On the one hand, during application, hazardous substances in such confined and poorly ventilated spaces can pose safety risks. On the other hand, water quality must be safeguarded to prevent harmful residue from affecting health and the lifespan of aquatic life.

The waterproofing and anti-corrosion coating systems used in pools now include epoxy composites, polyurethane coatings, and reactive polyurea coatings. What are the different functions of these materials, and how do we choose the right ones for application?

Before selecting materials, we must understand the advantages and disadvantages of the current materials.

1. Epoxy composite systems: Refer to fiberglass and epoxy resin composites widely used for their high hardness and strength, low-cost formulation, and ease of use. However, they are relatively brittle and not very weather-resistant. Fiberglass can significantly enhance their toughness, enabling waterproof applications.
2. Polyurethane coatings: Generally consist of isocyanate prepolymers (also known as low molecular weight urethane polymers) and polyether polyol resins. Polyurethane has high strength and weatherability, with high elongation at break that other materials cannot match. Its polyol component is common and much cheaper than epoxy resin, but it has the disadvantage of poor operability due to the necessary use of aromatic isocyanates, prone to bubbling and high outdoor application risk.
3. Polyaspartic polyurea coatings: Specifically refer to polymers of polyaspartic ester resins and polyisocyanates. A favorite in water parks, these materials have high strength, good weatherability, and toughness, with fast drying times but at a higher cost.
4. Spray polyurea coatings: Typically made from polyetheramines and isocyanate prepolymers. These coatings are characterized by ultra-fast drying and high strength, in addition to allowing a high build in a single application. The downsides are the need for professional equipment and operators, the necessity for special adhesion treatment, and higher costs.

Having understood the material properties, how should we choose the right ones for application?

Firstly, we exclude cost and ease of application since they don't greatly impact the clear pros and cons of the coating systems we're evaluating. Next, we eliminate hardness as it is not a decisive factor. What remains are adhesion, resistance to hypochlorous acid, elongation at break, tensile strength, and toughness.

Clear adhesion advantage:

In pool coating systems, local detachment of coatings is common, usually due to insufficient interlayer adhesion - this might be inherent to the material application or develop over time due to substrate shrinkage, coating stress contraction, or anion permeation. The detachment can occur between layers: the substrate, primer, mortar layer (interface layer), intermediate coat, topcoat, and sealant. Generally, detachment is less common between the primer, mortar layer, and intermediate coat due to careful design consideration of adhesion which is also easier to solve. The topcoat and sealant are typically made from the same material, differing only in color, and sometimes a sealant isn't necessary. Since their thickness doesn't exceed 0.2mm, the adhesion issue between them is not significant.

For intermediate and topcoats, differing material systems have different thermal expansion rates, so after thermal cycling, the same material system will have better adhesion than dissimilar systems. Moreover, in swimming pools, water treated with disinfectants leaves plenty of Cl¯ and OCl¯, some of which permeate through the topcoat to the intermediate layer, causing detachment. Polyurea outperforms polyurethane in preventing Cl¯ and OCl¯ permeation.

For the substrate and primer, the primer's role is to enhance adhesion and seal capillaries. If the primer fails, especially under high summer temperatures, water vapor more easily penetrates the mortar layer's cracks, exerting significant pressure and causing detachment.

Crack resistance:

When the pool’s concrete structure cracks, the waterproofing layer must accommodate the deformation without rupture. This means the waterproofing material must be able to stretch sufficiently across the crack's width. Given that concrete cracks generally don't exceed 2mm, an elongation at break of over 400% is usually enough to bridge such cracks.

Resistance to hypochlorous acid:

Hypochlorous acid is the main disinfectant in pools, and resistance to it is vital for maintaining the waterproofing layer's integrity. Polyurethane and polyurea generally have good resistance to hypochlorous acid.

Polyaspartic Polyurea Waterproof Coatings are suitable for long-term submerged environments and can be used for waterproofing applications in swimming pools, landscape pools, firefighting pools, and other areas expected to be immersed in water for extended periods. They are also appropriate for indoor waterproofing solutions in bathrooms, kitchens, balconies, as well as in other waterproof environments such as sauna shower rooms and SPAs. This product addresses the significant decline in performance of conventional water-based waterproof products on the market after prolonged water exposure. At the same time, it avoids the drawbacks of using polyurethane oil-based waterproof coatings in firefighting pools, drinking water pools, etc. Polyaspartic polyurea has now become a mainstream waterproof material worldwide.

Feiyang has been specializing in the production of raw materials for polyaspartic coatings for 30 years and can provide polyaspartic resins, hardeners and coating formulations. Some of our polyaspartic coating formulations: Polyaspartic Coating

Feel free to contact us: marketing@feiyang.com.cn

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