Fiberglass Pool Installation – Backfill and Soil Types

Understanding Ground and Soil Requirements for Fiberglass Swimming Pool Installation

As a company that is deeply passionate about swimming pool installation and construction, we know that using the correct backfill (the material used to pack around and level your pool), when based on the soil types of your fiberglass pool installation, is crucial. However, it’s reassuring to know that due to their durability, flexibility, and all-in-one construction, fiberglass pools are perfectly ideal even under adverse soil conditions—especially shrink-swell. This includes just about any other soil type, whether it is sand, rock, or clay. Fortunately, modern prefabricated fiberglass pool shells are both durable and extremely adaptive to installation in numerous ground types, making them the most versatile pool available when it comes to soil conditions.

Nevertheless, the backfill and soil conditions where you install your swimming pool can significantly impact the installation process and— if not properly addressed— could even affect the long-term stability of your pool. But why is this choice so important?

Backfill and soil types play a pivotal role in ensuring the structural integrity and longevity of your fiberglass swimming pool, and the success of your pool installation hinges on getting this fundamental step right. There are different requirements and concerns associated with different backfill and soil types, and having a thorough understanding of what those are can save you time, money, and potential headaches down the road.

What are the different types of backfill used during Fiberglass Pool installation?

When it comes to installing a fiberglass swimming pool, the type of backfill you choose sets the foundation for everything. Let’s delve into the common types of backfill used for fiberglass pool installations and the considerations for each.


Sand is commonly used as a backfill and base for fiberglass pools and has been used for many years with great success. It provides good drainage and is relatively easy to work with during installation. Sand also has the added benefit of being a very good insulator for your fiberglass pool. While sand is easy to work with it is best to have a very experienced installer use this material to ensure that there will not be any settling during or after the installation process.


Gravel is a sturdy choice for fiberglass pool installation. It offers excellent drainage and stability, making it suitable for area of heavy rainfall and poor soil conditions. Gravel used in fiberglass pool installation should be roughly 3/8” chipped in size and of a “cleaned” or “washed” variety to ensure there will not be any erosion of the finer particulate within the backfill. A proper base layer is crucial to ensure the pool remains level and support the pool’s weight evenly. Gravel can be easily compacted to fully support the shell.

The type of backfill involved in your fiberglass pool installation may be the most important factor in the long-term success of your pool installation. Each backfill has its advantages and considerations, and the suitability of one over the others depends on many factors including soil type, climate, and location. Understanding these concerns will help ensure successful and enjoyable swimming pool ownership for many years to come.

In choosing the ideal site for your pool installation, the soil should ideally be consistent beneath and in the surrounding the pool shell, and stable enough to prevent shifting. Your pool installer should be knowledgeable when it comes to soil engineering and able to determine if there’s a need for additional support features, soil injection, or extra drainage.

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How Does Soil Composition Affect Fiberglass Pool Installation?

Soil composition can play a significant role in determining the stability and longevity of your pool. Let's explore this crucial aspect further.

Sandy Soil:

Sandy soil is well-draining but lacks cohesion. While it doesn't expand or contract significantly with changing moisture levels, it may not provide the necessary support for your pool. To install a fiberglass pool on sandy soil, additional measures for compaction for the base and surrounding walls may be required to ensure stability.

Clay Soil:

Clay soil retains moisture and can expand significantly when wet and shrink when dry. This expansive nature can pose challenges to fiberglass pool installations. Proper drainage solutions and soil stabilization techniques are important to prevent soil movement and protect your pool. It can take some special expertise to install fiberglass swimming pools in high clay areas. Areas where such soil is common may also suffer from high water tables, making it more difficult to install a fiberglass pool. Improper installation under these conditions can cause serious problems down the road.

Loam Soil:

Loam soil, with its balanced mixture of sand, silt, and clay, is often considered ideal for fiberglass pool installations. It offers good drainage while maintaining some structural stability. However, it's essential to assess the specific characteristics of your loam soil to ensure it meets the requirements for your pool.

Rocky Soil/ Solid Rock:

Rocky soil and Solid Rock can be both a blessing and a challenge. While it provides excellent support, drainage in these soil types tend to be poor. Digging through rocks during excavation can be labor-intensive and costly. Proper excavation techniques and equipment are essential when dealing with rocky soil to avoid damage to the pool shell.

Soil composition is crucial because it directly affects the installation process and the long-term performance of your fiberglass pool. Soil testing and consultation with professional pool installation specialists can help you determine the best approach to address your specific soil type.

What Factors Affect Soil Stability for Fiberglass Pool Installation?

Being aware of the factors that can affect soil stability during fiberglass pool installation is essential to ensure your pool remains secure and free from potential issues.

Water Table Level:

The water table refers to the depth at which groundwater is found in the soil. If the water table is too high in your area, it can create hydrostatic pressure against your pool shell, potentially causing it to lift or crack. Proper drainage systems can help manage water table issues.

Underground water pooling can directly affect the stability of your pool. A fiberglass pool shell is comparable to a huge container, and it could be displaced if a substantial amount of water accumulates beneath it. This can occur when the pool is drained and there is no counterweight from the underground water. Expansive soil (soil that shrinks or swells dramatically depending on moisture levels) can place undue pressure on swimming pool walls. Proper installation is necessary to ensure durability and requires the correct amount of soil or backfill, drainage, and support.

Climate and Weather Conditions:

Climate plays a significant role in soil stability. In regions with extreme temperature fluctuations, soil can experience much more severe expansion and contraction, affecting the pool's foundation. Proper insulation and soil preparation are vital to counteract these effects.

Vegetation and Trees:

The presence of large trees or dense vegetation near your pool can also impact the stability of the soil. Tree roots can draw moisture from the soil, leading to uneven settling. It's essential to consider tree removal or root barriers to protect your pool's structural integrity.

Soil Compaction:

Proper soil compaction is critical to ensure a stable foundation for your fiberglass pool. Inadequate compaction can lead to settling, which may result in an uneven pool surface or damage to the pool shell. Professionals should use compaction equipment and techniques suitable for your soil type. Using the proper material to backfill the spaces around the pool shell will create the necessary back pressure (while maintaining desired flexibility) to maintain proper pool stability. 

What Precautions Can You Take for Soil-Related Concerns in Fiberglass Pool Installation?

Professional Site Assessment:

Start by having your site assessed by a qualified pool installer or geotechnical engineer. They can evaluate the soil composition, water table, and other site-specific factors to recommend the best installation approach.

Proper Excavation and Compaction:

Ensure that the excavation and soil compaction are carried out meticulously. This includes using the best available equipment and techniques to create a stable base for your pool.

Drainage Solutions:

Implement effective drainage solutions to manage excess groundwater, especially in areas with high water tables. A well-designed drainage system will alleviate and prevent hydrostatic pressure issues.

Regular Maintenance:

Keep an eye on your pool's surroundings. Monitor trees and vegetation that could affect the soil, and promptly address any issues that arise to maintain soil stability. Keep your eye out for indications that the area around the pool is shifting, sinking, or settling, and if so, notify your pool installer immediately to remedy the situation.

Consultation and Professional Expertise:

Don't ignore the recommendations of your experienced pool installer. Their knowledge and expertise is invaluable in ensuring a trouble-free installation.

By taking these precautions and staying informed about the unique soil-related concerns in your area, you can enjoy your fiberglass pool with confidence, knowing it's built on a stable and secure foundation.

Now that you have a better understanding of the critical role that backfill and soil types play in fiberglass pool installation, it may be time to reach out to a qualified pool installer who can evaluate your specific location, soil composition, and potential concerns. Armed with this knowledge, you'll be well-prepared to make the best decisions about your fiberglass pool project, ensuring a safe, stable, and enjoyable swimming experience for years to come.

At Barrier Reef Pools, we encourage you to browse our wide selection of beautiful fiberglass swimming pools. For any questions, please contact us here or reach out to us on our social media listed below. We would love to help you find your new pool!