What Is Backfilling A Pool?

Have you ever seen an inground pool shift out of the ground or sink into the ground? This can happen if a pool is not properly backfilled. As far as inground pool construction goes, one of the most important and overlooked steps is backfilling a pool.

Well, “what is backfilling a pool?”, you may be wondering. Backfilling is the process of filling the space around the outside of the pool shell with a supportive material after the pool has been set in the excavation. Backfilling is critical for the stability, longevity, and overall performance of your pool. A pool cannot just sit in the ground; it needs some sort of support from the ground shifting, groundwater, etc.

At Royal Pools G2 Landscaping, we install fiberglass and vinyl liner pools. Although we do not install concrete pools, we love educating clients about all the options.

In this article, we’ll explain what pool backfill is, why it’s important, and the materials typically used. Most importantly, we will break down how the process differs depending on pool type.

Why Is Pool Backfill Important?

When a hole is dug for an inground pool, the hole is always larger than the pool shell. This extra space gives the installer room for proper placement, plumbing, and adjustments during installation. These gaps cannot remain, however. Leaving the gaps unfilled would cause the pool walls to collapse, shift, or flex over time.

Backfilling a pool provides key support to an inground pool, including:

• Structural Support: Backfill holds the pool shell securely in place.
• Drainage Control: The right material allows groundwater to drain away instead of putting pressure on the pool walls.
• Ground Stability: Prevents soil erosion and shifting around the pool.
• Longevity: Proper pool backfill reduces the risk of wall bulges, cracks, or liner issues.

Common Pool Backfill Materials

“What is used to backfill the pool?” Great question. You’d be forgiven for assuming the excavated dirt is going back in the ground to backfill around the pool. Backfilling a pool requires stronger material.

The backfill material is what will determine the long-term success of your inground pool construction. Although backfill materials have changed over time, modern inground pool backfills should be made of:

• Clean Crushed Stone or Gravel: Crushed stone or gravel is the best option for inground pools. It provides excellent drainage and doesn’t compact over time.

Backfilling a Fiberglass Pool

Fiberglass pools are manufactured shells that are lowered into the excavated hole. Rather than being built entirely onsite, like concrete and vinyl liner pools, fiberglass pool shells are built in controlled facilities and then transported to their forever homes. Because these shells are relatively lightweight and flexible, they need stable support to prevent shifting or wall movement.

For fiberglass pools, clean crushed stone is the best pool backfill material. It compacts naturally, allows for proper drainage, and reduces hydrostatic pressure around the pool walls. Typically, installers will lay the pool base with the compacted gravel backfill before the pool is lowered into the hole.

Backfilling a Vinyl Liner Pool

Vinyl liner pools are built with wall panels and a custom liner that sits inside the structure. After the walls are established, the space behind them must be backfilled to prevent the walls from collapsing over time, destroying the liner.

At RPG2, we use and recommend crushed stone or gravel for backfilling vinyl liner pools. In areas with high groundwater, gravel or crushed stone will always be the best possible option for keeping your pool secure and durable for years to come.

Backfilling a Concrete Pool

Concrete (or gunite/shotcrete) pools are structurally different from fiberglass and vinyl liner pools. The concrete shell itself is built strong enough to resist external pressures, but backfilling still plays a role in the construction process.

• Timing: Backfilling is done after the concrete shell is formed and cured.
• Materials: Like fiberglass and vinyl liner pools, gravel or crushed stone is the best backfill material for concrete pools. Particularly for the base of the backfill. Some contractors will use a combination of dirt and gravel for the middle layers of a concrete pool backfill.
• Importance: Even though the walls are self-supporting, poor backfilling can cause settling around decks, plumbing shifts, or drainage issues that damage the pool environment.

Best Practices for Pool Backfilling

1. Backfill and Fill Together: Always add water to the inside of the pool at the same time as you add backfill around the outside. This balances pressure and prevents the pool walls from bowing.
2. Compact in Layers: Backfill should be added gradually and compacted in layers to ensure stability.
3. Use the Right Material: Gravel or crushed stone is the best backfill material for inground pools.
4. Don’t Cut Corners: Improper backfilling can cause costly problems such as wall bulging, cracking, or premature liner replacement.

Conclusion

Backfilling a pool is perhaps the most critical step during an inground pool construction project. Whether you’re installing a fiberglass pool, a vinyl liner pool, or a concrete pool, using gravel backfill material will guarantee a successful installation, thus ensuring the durability and longevity of your pool.

Do you have more pool questions? If so, check out the articles below. For even more educational content on all things pools and landscaping, check out our learning hub at the top of our page. See you next time!

How to Measure a Swimming Pool Liner?

Which Type of Pool Filter Is the Best?

What Is A Fiberglass Pool Shell?

Written by Logan Edgemon