When setting up an above ground pool, many homeowners focus on the size, shape, and accessories—but often overlook one of the most critical aspects of installation: the surface underneath the pool. A proper base not only enhances the stability and longevity of your pool but also contributes to safety, comfort, and drainage. If you’re wondering, “What is best to put underneath an above ground pool?”, this comprehensive guide will help you understand your options, how to choose wisely, and what to avoid.
Understanding the Importance of the Pool Base
Before diving into materials, it’s essential to understand why the foundation matters. The base beneath your above ground pool performs several crucial functions:
- Distributes weight evenly to prevent sinking or shifting
- Protects the pool liner from punctures or abrasions
- Provides a level and smooth surface for the pool structure
- Helps with drainage and moisture control
Improper preparation can lead to costly repairs or even premature pool replacement. This is especially important when investing in a steel or vinyl-lined above ground pool, as sharp objects or uneven surfaces can easily damage the liner.
Key Factors to Consider When Choosing a Base Material
Not all surfaces are appropriate for every pool. Before you break ground, consider the following:
Pool Size and Weight
Larger pools exert more pressure on the base. Heavier structures, particularly during winter when water is left in the pool, require a more robust foundation.
Drainage Requirements
Water doesn’t drain through vinyl or concrete. Without proper grading and base materials, pooling water can cause mold, algae growth, or structural damage.
Local Climate
If you experience freezing winters, the ground can expand and contract beneath your pool. This can warp the base structure if not properly insulated or stabilized.
Surrounding Landscape
If your yard slopes, has tree roots, or contains rocky soil, special care must be taken with site preparation and base material selection.
Top Materials to Place Under an Above Ground Pool
Now let’s explore the best materials you can use for the base beneath your above ground pool. Each option suits different needs, budgets, and regional landscapes.
1. Sand
Sand is one of the most commonly used materials for cushioning a pool’s bottom and protecting the liner. It’s versatile, affordable, and relatively simple to install.
- Pros: Provides a soft, even surface that conforms to slight imperfections in the ground
- Cons: Does not provide a firm base for large or heavy pools; can shift over time
When using sand, opt for washed masonry sand, which has been sifted to remove rocks and other sharp objects. Avoid using beach or play sand, as these may include materials that can damage your pool.
How to Install Sand Under Your Pool:
- Clear the area of grass, rocks, and roots
- Level the ground as much as possible
- Spread a layer of sand (2–3 inches thick)
- Compact lightly to set the base
Sand works well in climates that don’t experience heavy frost or extreme weather.
2. Foam Padding
Foam underlayment, often used in conjunction with sand or concrete, adds an extra layer of protection between the pool floor and its base.
- Pros: Acts as a cushion and protector for pool liners
- Cons: Does not serve as the sole base and can compress unevenly
Foam padding typically comes in 4×8-foot sheets and should be specifically pool-rated and UV-resistant. The best foam underlayment is at least 1/4 inch thick and is ideal for use under vinyl-bottom pools to prevent scuffing and punctures.
How to Install Foam Padding:
- Place a base layer of sand or concrete
- Trim the padding to fit the pool’s diameter
- Lay sheets flush against each other, without overlapping
Foam padding requires a stable, smooth subsurface to perform effectively and is best for smaller, temporary or seasonal pools.
3. Concrete Slab
A poured concrete base offers the most durable and long-term solution for installing an above ground pool.
- Pros: Extremely stable, prevents ground movement, ideal for permanent installations
- Cons: Expensive, time-consuming, requires professional installation
Unlike sand, a concrete base won’t shift or settle over time, and offers a perfectly level surface. Additionally, concrete prevents the growth of mold or roots underneath the pool—offering a clean, sealed base.
How to Prepare a Concrete Base:
- Measure the pool footprint and add extra space (at least 8–12 inches around the perimeter)
- Excavate to the required depth (typically 4–6 inches below frost line, depending on region)
- Pour a 3–5 inch concrete slab, reinforced with wire mesh or rebar for strength
- Allow the slab to cure completely before installing your pool
A concrete base is particularly ideal in cold or wet climates, where frost heaves and runoff can damage a less-secure foundation.
4. Gravel
Gravel, often used as a sub-base for concrete, can also support above ground pools directly, especially in conjunction with a tarp or sand layer.
- Pros: Excellent drainage, cost-effective
- Cons: Must be compacted carefully or installed with a capping layer to prevent sharp edges
While gravel alone can be too rough for pool liners, combining it with a layer of landscaping fabric and sand creates a stable, drainable base that still protects the pool.
How to Install a Gravel Base:
- Remove all vegetation and organic matter
- Excavate the area 4–6 inches down
- Layer landscaping fabric to suppress weeds
- Pour 3–4 inches of crushed gravel
- Compact the gravel and top with a 2-inch layer of sand or foam padding
This option works especially well for seasonal pools in regions with moderate weather.
5. Interlocking Foam Tiles
A newer and increasingly popular product, interlocking foam tiles offer a combination base and padding system specifically designed for above ground pools.
- Pros: DIY-friendly, quick to install, provides insulation and cushioning
- Cons: Higher upfront cost, not suitable for very large or permanent installations
These tiles are made from durable EVA foam, are resistant to water, and are easy to clean. Because of their modular nature, they can be easily removed or reinstalled seasonally.
How to Install Interlocking Foam Tiles:
- Level the ground as flat as possible
- Install a weed barrier fabric to reduce lawn growth and maintain stability
- Begin laying the tiles from the center outward
- Ensure the interlocking edges are fully engaged
Foam tiles are especially beneficial for individuals seeking comfort underfoot and additional insulation in cooler environments.
Which Base Best Suits Your Pool?
To make an educated decision, it helps to break down your needs by comparing each material side by side:
| Material | Best For | Budget Level | Installation Difficulty |
|---|---|---|---|
| Sand | Small pools, temporary use, budget installations | Low | Easy |
| Foam Padding | Added liner protection, seasonal use | Medium | Easy |
| Concrete Slab | Large, permanent pools and cold climates | High | Hard |
| Gravel with Sand Cap | DIYers, wet or hilly regions | Low to Medium | Moderate |
| Interlocking Foam Tiles | Fast setup, comfort, and insulation | Medium to High | Very Easy |
The “best” material depends on your installation goals, climate, and budget.
Common Mistakes to Avoid When Installing the Base
Even with the right material, incorrect installation can lead to problems. Here are some typical errors and how to avoid them:
Skipping Ground Preparation
Some homeowners believe that “a layer of sand hides imperfections.” This simply isn’t true. Uneven terrain or rocks can create pressure points that weaken your pool structure or puncture the liner over time.
Using the Wrong Type of Sand
Play sand and beach sand can contain shells, rocks, or excess silt. Use washed masonry sand for a grit-free base.
Improper Drainage Setup
A concrete base that doesn’t slope slighty away from the center can trap moisture, which could damage the pool’s structural integrity over time.
Choosing Thickness Without Planning
Laying too thick a layer of sand can cause soft spots, while too thin a layer won’t offer effective protection. Stick to the recommended 2–3 inches when using sand.
Not Leveling the Base
An unlevel foundation can cause the pool walls to bow, leak, or collapse over time. Always use a level and strike lines or strings to ensure a balanced base.
Forgetting Climate Conditions
In colder climates, choose materials that can handle freezing temperatures and snow removal tools. Foam padding may get damaged by heavy snow shovels, while concrete resists this better.
Step-by-Step Guide to Installing a Pool Base
To ensure you get this right, here’s a simple guide to preparing the area for your above ground pool:
Step 1: Select and Clear Your Site
Choose a flat, open area away from trees and structures. Mark the circle or oval shape of your pool with spray paint or rope.
Step 2: Remove Grass and Debris
Use a sod cutter or shovel to strip grass and roots. Clear away rocks, sticks, and any sharp objects from the soil.
Step 3: Level the Ground
Use a rake, shovel, and long 2×4 board with a level to ensure the ground is flat. Fill low spots with dirt or sand.
Step 4: Install Your Base Material
Depending on your choice, lay a layer of sand, install foam padding, pour concrete, or use interlocking tiles.
Step 5: Add a Liner Protection Layer (Optional)
If you don’t have a built-in protective pad in your pool, adding an extra foam or felt underlayment over the base material will provide an additional guard against rough points or ground unevenness.
Step 6: Install Your Pool
Assemble the pool on top of the base, ensuring it sits perfectly flat and that the walls are taut and secure.
Final Thoughts
The foundation you choose for your above ground pool can make the difference between a fun-filled summer and a costly disaster. Whether you opt for budget-friendly sand, long-lasting concrete, or the modern foam tiles, the key is to balance affordability, durability, and protection for your specific needs.
By properly planning and preparing the surface underneath your pool, you ensure greater enjoyment, reduced maintenance, and a longer lifespan for your pool. Take the time to explore your options, weigh the pros and cons, and invest in a solid foundation for one of your most cherished backyard spaces.
What materials are best to use as a base under an above ground pool?
The ideal materials for an above ground pool base include sand, concrete, solid foam padding, or specialized pool base kits. Sand is a popular choice because it’s affordable, easy to spread, and provides a soft and level surface. However, while sand offers great cushioning, it may shift over time, especially in wet or uneven ground conditions. Concrete provides a durable and stable base but can be expensive and labor-intensive to install.
Another excellent option is using a solid foam base, which combines the softness of sand with the stability of solid material. These foam pads are designed specifically for pools, help prevent wear on the pool’s liner, and offer insulation against temperature extremes. Specialized base kits with blocks and leveling systems are also available, allowing for adjustable support and a durable foundation. Choosing the right material depends on your budget, the terrain, and the expected lifespan of the pool.
Why is it important to use the right base material under an above ground pool?
Using the correct base material is critical because it affects the pool’s stability, longevity, and safety. An improper or uneven base can lead to structural damage to the pool’s walls and floor, and can also cause the pool to tilt, creating dangerous conditions. The right base not only ensures proper weight distribution but also protects the liner from sharp or rough ground elements, such as rocks and roots, which can cause punctures or tears.
A good base also contributes to comfort and usability. A flat, smooth surface makes for a better swimming experience and helps avoid discomfort for swimmers walking on the pool floor. Additionally, proper bases can help with water drainage and prevent moisture from accumulating underneath the pool, which can lead to mold or ground erosion over time. By investing in the proper base, you help protect your pool and enhance the overall enjoyment of the installation.
Can I use just sand under my above ground pool?
Sand is a commonly recommended material for underneath above ground pools due to its flexibility and ease of use. It works well on relatively flat and cleared ground, where it can be raked and leveled to create a smooth, even surface. Sand provides a stable base that conforms to the ground while offering some cushioning to protect the pool liner from sharp objects.
However, sand is not suitable for all backyard conditions. On sloped or uneven terrain, it can shift or wash away during heavy rain, leading to instability and potential damage to the pool. In such cases, a combination of ground leveling and more secure materials, such as foam padding or concrete blocks, might be necessary. If you do opt for sand, ensure that it’s evenly spread and free of debris to maximize effectiveness and longevity.
Should I remove grass before putting an above ground pool on the ground?
Yes, it is highly recommended to remove grass and vegetation before placing an above ground pool. Grass and plants beneath the pool can retain moisture, attract insects or small animals, and eventually decay, leading to mold or uneven ground under the pool. Leaving grass intact may also allow roots to regrow and create bumps or damage the pool’s base over time.
Proper preparation involves removing the top layer of grass and topsoil to achieve a firm and level surface. After the grass removal, compacting the soil is important to prevent settling or shifting once the pool is installed. After this, you can add your chosen base material, such as sand or foam, for a clean and stable foundation that supports the pool evenly and safely.
Is solid foam padding better than sand under an above ground pool?
Solid foam padding is often considered superior to sand in certain situations because it provides a smoother, more consistent surface that doesn’t shift or erode. Foam padding is specially designed for pool installations and acts as a protective layer between the ground and the pool liner. It also offers excellent insulation, which is beneficial in areas with fluctuating temperatures or cold ground conditions.
However, sand remains a more affordable and widely available option, especially for temporary installations or pools in relatively flat areas. While sand may require more maintenance over time due to settling or unevenness, it can still be an effective base if properly installed. Ultimately, the decision between foam padding and sand depends on your priorities—whether you value initial cost-effectiveness (sand) or long-term protection and stability (foam padding).
What should I avoid putting under my above ground pool?
Certain materials should be avoided when preparing the base for an above ground pool. These include large rocks, dirt clods, concrete pavers without a leveling system, plastic sheets, or any sharp or uneven objects. These can cause damage to the pool liner, provide an unstable or uncomfortable surface, or trap moisture, leading to mold and ground erosion.
Plastic sheets or other impermeable materials underneath the pool can prevent proper drainage and trap moisture, potentially leading to water accumulation and damage over time. Avoid using mulch or organic materials like leaves or wood chips, as they can decompose and shift under the pool’s weight. Choosing inappropriate materials may reduce the pool’s stability and lifespan, so always prioritize a smooth, level, and durable base.
How do I level the ground before putting an above ground pool in place?
Leveling the ground is one of the most important steps in preparing for an above ground pool installation. Start by clearing the site of grass, rocks, sticks, and other debris. Using a shovel and rake, excavate high spots and fill in low areas to create a flat surface. A carpenter’s level or laser level can be used to check for evenness.
Once the ground is roughly leveled, compact the soil using a hand tamper or mechanical compactor. This prevents settling after the pool is filled. After compacting the soil, you can add a layer of your preferred base material—like sand or foam padding—and smooth it out with a board or screed. Continuously check for levelness throughout the process, as even a slight slope can lead to big problems once the pool is installed and filled with water.