Which pool liners should I choose?

You have the project, the land, perhaps already an idea of the shape of your pool. But when your pool builder asks you, "flat bottom or sloped bottom?", doubt sets in. This is normal: this decision is rarely explained clearly, even though it affects your swimming comfort for 20 or 30 years.

For a fiberglass shell pool, the bottom is integrated into the structure from the moment of manufacture: it is impossible to modify it after installation.

The right choice depends on who uses your pool, your lifestyle, and your budget. This guide provides everything you need to make an informed decision.

What is the bottom of a prefabricated pool, and why is this choice so important?

In a fiberglass shell pool, the term "bottom" refers to the interior floor of the pool, meaning the horizontal surface on which swimmers' feet rest. This floor can be flat, gradually sloped, or incorporate areas at different levels depending on the chosen configuration.

What distinguishes a shell pool from a concrete-built pool is precisely the irreversibility of this choice: the shell is manufactured in a factory in one piece, by polyester lamination. The shape of the bottom is an integral part of the structure, just like the overall shape of the pool or its dimensions. This is why the bottom is not chosen in isolation: it is part of a global choice of pool model to be considered from the outset, taking into account the actual use of the pool and the profile of your household.

In practice, the pool liner affects four key aspects of your swimming experience:

• Safety (slip hazard, accessibility for children and seniors),
• Comfortable swimming (swimming, games, water aerobics),
• Ease of maintenance (robot movement, debris buildup),
• and finally, accessibility for people with disabilities in certain specific cases.

As many criteria as it is better to anticipate from the first meeting with your pool builder.

Flat bottom or sloped bottom: What practical differences does this make for your use?

Flat bottom or sloped bottom? Both options have their own advantages, and the right choice depends above all on the composition of your household and the intended use of the pool.

The flat bottom: versatility and ease of maintenance

A flat bottom, as its name suggests, offers a uniform depth over the entire surface of the pool. This depth is generally between 1.20 m and 1.50 m for common family models. It is the most widespread configuration, and for good reason. It is suitable for recreational swimming, water games, aquagym, and gentle swimming.

The cleaning is made as easy as possible: automatic robots move on a perfectly uniform surface, without having to manage changes in slope. Debris (leaves, insects, sand) does not accumulate in any particular area.

For families with children of various ages, a flat bottom at 1.30 m often represents the best compromise.

The sloped bottom: a natural progression, ideal for blended families

The sloping bottom offers a progressive slope from a shallow area (generally around 0.90 m) to a deeper adult area (1.40 m to 1.80 m depending on the models).

This layout recreates a more natural swimming experience, similar to walking into the ocean. It is particularly popular with families with young children, as the shallow area provides a safe play space on the “beach” side. However, this layout has a practical drawback: debris tends to drift toward the deepest area due to water circulation. Manual vacuuming may be necessary in addition to the automatic robot.

Here is a comparison chart to help you quickly determine which configuration best suits your needs:

Criterion	Flat bottom	Sloping bottom
Depth	Uniform (1.20–1.50 m)	Progressive (0.90–1.80 m)
Primary use	Family / Leisure / Relaxation	Coed / Leisure Swimming
Robot Maintenance	Optimal, linear path	Well, there is a slight concentration of deposits in the deep zone
Comfort for children	Provides safety across the entire surface	A shallow area designated for children
Diving	Not recommended	Not recommended unless the water is very deep (≥ 1.80 m)
Ease of maintenance	Very easy	Slightly more complex

What bottom depth should you choose based on your usage profile?

Reference depths based on the swimming profile

Choosing an unsuitable depth (too shallow for adult swimmers, or too deep for a family with young children) is one of the most frequent mistakes in swimming pool projects. And as with the choice of the pool floor, it is impossible to correct it once the shell is installed.

The following table summarizes the recommendations usually adopted by shell pool professionals, according to different usage profiles:

User Profile	Recommended depth	Point to watch out for
Young children	0.80–1.00 m	Mandatory supervision; safety barrier required
Blended family	1.20–1.40 m	A flat or slightly sloped surface is recommended
Adult swimmers	1.40–1.60 m	Flat bottom for a swimming lane
Diving	≥ 1.80 m (regulated)	This should be addressed as early as the design phase

What do the regulations say about the minimum depth?

Unlike public swimming pools, private pools are not subject to national regulations setting a minimum legal depth. However, diving requires strict safety precautions: industry experts recommend a minimum depth of 1.80 m to 2.00 m below the landing area.

If this use is considered, it must be mentioned from the design phase. Legal obligations regarding pool safety (barriers, alarms, covers) apply to all configurations, regardless of the chosen depth.

Flat bottom or sloped bottom: which one is really easier to maintain?

Pool maintenancerepresents a significant daily expenditure of time and budget. And the shape of the bottomdirectly influences the frequency and ease of this maintenance. This is an aspect that many owners underestimate when choosing their pool.

How the surface affects dirt buildup

On a flat surface, automatic cleaning robots move linearly and cover the entire area homogeneously. Debris (leaves, insects, dust) are evenly distributed and easily vacuumed up as the robot passes.

On an inclined surface, suspended particles in water naturally tend to slide towards the deepest area under the effect of gravity and water circulation. The robot can access this area, but manual vacuuming in addition is often still recommended, especially after a period of strong sunlight or wind.

The role of gelcoat in ease of cleaning

Regardless of the type of background, the quality of the interior coating plays a major role in ease of maintenance. The polyester gelcoatof a quality shell pool offers a non-porous, smooth, and waterproof surface, which greatly limits the adhesion of algae and limescale deposits.

At Aboral Piscines, the Sparkle finishes (available on pools in the TAILOR MADE range) incorporate reflective particles that enhance this effect while providing a premium visual finish. The Iconic Grey, Pacific Blue, Silver Grey, and Mineral Sand colors in this range sacrifice nothing in terms of durability and ease of maintenance.

How does Aboral Piscines help you choose the right pool liner for your project?

At Aboral Piscines, each project begins with an on-site visit to analyze the property's configuration, soil type, the future pool's orientation, and intended uses. Based on these elements, consultants propose a selection of suitable models(with corresponding bottom options) accompanied by a visual representation and transparent cost estimate.

The range includes flat-bottomed and sloped-bottomed pool models, and custom configurations for projects requiring a bespoke approach. For over 30 years, this end-to-end support approach has helped avoid design errors that would be difficult to correct after installation.

Choosing the bottom of your shell pool means defining the swimming experience you will have for years to come: your children's safety, the ease of your weekly maintenance, and the comfort of your swimming. And since it is a definitive choice, it deserves to be made with the same care as the size of the pool or its location in the garden.

Building a swimming pool is above all a life project that commits your property in the long term. The good news is that the options available today make it possible to meet almost all family situations, from the simplest to the most specific, provided they are identified beforehand with the right contact person.

The experts Aboral Piscines are available to analyze your project and offer you the most suitable pool configuration for your home, your land, and your budget.