Laying down a protective barrier of landscape fabric and gravel before assembling your pool prevents grass from rotting and keeps mud from splashing onto the liner. If you are wondering exactly what to put under above ground pool on grass, the answer depends on the pool type, your yard’s slope, and how long you plan to keep the pool up. This guide walks you through every layer, from the ground up, so you can set up your pool correctly the first time.
Grass under a pool will die within days because it gets no sunlight and the water pressure suffocates the roots. That dead grass then turns into a slimy, smelly mess that attracts insects and can degrade your pool liner over time. The goal is to create a smooth, level, and protective base that separates the pool floor from the soil and vegetation below.
Why You Cannot Put A Pool Directly On Grass
Many first-time pool owners skip the base layer to save time, but this is a mistake. Putting a pool directly on grass leads to several problems that could ruin your summer fun.
Grass Rot And Odor Problems
When you trap moisture under a pool, the grass begins to ferment and rot. This process produces hydrogen sulfide gas, which smells like rotten eggs. The odor will seep through the liner and make the water smell unpleasant. You also create a breeding ground for mold, mildew, and fungus.
Uneven Surface And Punctures
Grass is never perfectly flat. Small bumps, roots, and rocks underneath will create pressure points on the pool floor. Over time, these pressure points can cause the liner to stretch, weaken, and eventually puncture. A single tiny stone can cause a leak that ruins the entire pool.
Weeds And Insects Coming Through
Weeds are persistent. They will push through thin barriers and grow up into the pool. Ants and other insects will also nest under the warm, damp pool floor. Once they find a way in, you will have an infestation that is hard to control.
What To Put Under Above Ground Pool On Grass: The Base Layers
Now for the main event. The best setup involves a multi-layer system. You do not need all of these layers for every pool, but the more protection you add, the longer your pool will last.
Layer 1: Ground Preparation And Leveling
Before you put anything down, you must remove the top layer of grass. Use a sod cutter or a sharp shovel to strip away the grass and roots. You need to expose bare soil. This prevents the grass from rotting and creating that terrible smell.
After removing the grass, check the level. Use a long 2×4 board and a carpenter’s level. Place the board on the ground and check it in multiple directions. If the ground is uneven, remove high spots with a rake and add fill dirt to low spots. You want a slope of less than one inch across the entire pool footprint. A perfectly level base is critical for the pool walls to stand straight and hold water evenly.
Layer 2: Sand Or Pool Pad
Once the soil is level and compacted, you have a choice. You can spread a layer of mason’s sand, or you can use a manufactured foam pool pad. Sand is cheap and easy to shape. It conforms to the ground and provides a soft cushion. You want about one to two inches of sand spread evenly and then leveled with a long board.
Foam pool pads are a newer option. They are made from dense, closed-cell foam that does not absorb water. These pads are excellent at smoothing out small imperfections and providing thermal insulation. They are easier to install than sand because you just roll them out and tape the seams. However, they are more expensive than sand.
Layer 3: Landscape Fabric Or Tarp
Here is the critical protective barrier. You need a heavy-duty landscape fabric or a tarp to go between the sand and the pool liner. This fabric stops weeds from growing up and prevents sharp objects from poking through. It also keeps moisture from the ground from reaching the liner, which prevents mold and mildew.
If you use a tarp, make sure it is a woven tarp, not a thin plastic one. Thin plastic traps condensation and can cause the liner to stick and tear. Landscape fabric is better because it allows water to drain through while still blocking weeds and roots.
Layer 4: The Pool Liner Or Bottom
The final layer is the actual pool floor. If you have a metal frame pool with a separate liner, the liner sits on top of the landscape fabric. If you have an inflatable top ring pool, the bottom is already attached. In that case, the landscape fabric goes directly under the pool bottom. The key is that nothing sharp should be between the fabric and the pool floor.
Step-By-Step Installation Guide
Follow these steps in order to get the perfect base for your above ground pool. Take your time with the prep work, as it is the most important part of the entire setup.
- Measure your pool footprint. Add two feet to the diameter on all sides. This extra space gives you room to walk around the pool and adjust the walls.
- Remove the grass. Use a sod cutter for large pools or a flat shovel for smaller ones. Remove all grass, roots, and debris from the marked area.
- Level the soil. Dig down high spots and fill in low spots. Compact the soil with a hand tamper or a plate compactor. The surface should be firm and even.
- Spread the sand. Pour mason’s sand over the leveled soil. Use a rake to spread it, then drag a straight board across the top to level it. Spray the sand lightly with water to help it settle.
- Lay the landscape fabric. Roll out the fabric over the sand. Overlap the seams by at least six inches. Use landscape staples to hold it in place. Make sure there are no wrinkles or bumps.
- Install the pool. Follow the manufacturer’s instructions to assemble the pool frame and liner. Be careful not to drag the liner across the fabric, as this can cause friction tears.
- Fill the pool slowly. As the pool fills, stop occasionally to smooth out wrinkles in the liner. A small amount of water is fine, but do not let the pool sit half-filled for a long time.
Alternative Base Options For Different Pool Types
Not all pools are the same. The best base for a small inflatable pool is different from a large permanent above ground pool. Here are the options broken down by pool type.
Small Inflatable Pools
For small, seasonal pools, you can skip the sand and just use a thick tarp or a pool pad. These pools do not have the weight to cause major ground issues. The main goal is to protect the bottom from rocks and sticks. A simple tarp is often enough.
Metal Frame Pools
Metal frame pools need a full base. The vertical supports put a lot of pressure on the ground. You must have a level surface or the frame will twist and collapse. Use the full sand and fabric setup for these pools. The sand cushions the bottom, and the fabric protects the liner from the sand.
Hard-Sided Pools
Hard-sided pools are the heaviest and most permanent. They require a perfectly level base that will not shift. Many owners pour a concrete pad or use interlocking foam tiles. These options are more expensive but provide the best long-term support. If you use sand, make sure it is very compacted and deep.
Common Mistakes To Avoid When Prepping The Ground
Even with good intentions, people make errors when setting up their pool base. Here are the most common mistakes and how to avoid them.
- Skipping the level check. A pool that is off by just two inches can cause the water to be deeper on one side. This puts uneven pressure on the frame and can cause it to bow.
- Using a cheap plastic tarp. Thin tarps tear easily and trap moisture. Always use woven landscape fabric or a purpose-made pool pad.
- Not removing the grass. Some people think laying a tarp over grass is fine. It is not. The grass will die and decompose, creating an uneven surface and a bad smell.
- Forgetting about drainage. If your yard has poor drainage, water will pool under the pool. This can wash away the sand and cause the ground to shift. Consider adding a French drain or a gravel layer if you have heavy clay soil.
Do You Need Gravel Under The Pool?
Gravel is not always necessary, but it is helpful in certain situations. If you have very soft, muddy ground, a layer of crushed gravel can provide a stable base. The gravel should be compacted and then covered with sand to create a smooth surface. Gravel also helps with drainage, preventing water from pooling under the pool.
However, gravel is not a good idea for inflatable pools. The sharp edges of the gravel can puncture the thin bottom. If you use gravel, make sure it is topped with a thick layer of sand and a strong fabric barrier.
Maintaining The Base Over Time
Once the pool is up, you cannot see the base anymore. However, you should still think about it. Check the ground around the pool for signs of settling or erosion. If you notice the ground sinking on one side, you may need to add more sand or soil around the outside of the pool to support the walls.
At the end of the season, when you take the pool down, inspect the base. If the fabric is still in good shape, you can reuse it. If it is torn or has holes, replace it. The sand can be left in place or raked into the lawn.
Cost Breakdown For Pool Base Materials
Budget is always a concern. Here is a rough idea of what you will spend on materials for a standard 15-foot pool.
- Mason’s sand: $20 to $40 per cubic yard. You will need about half a yard for a 15-foot pool.
- Landscape fabric: $15 to $30 per roll. One roll is usually enough.
- Pool pad (foam): $50 to $100 depending on the size.
- Tarp (heavy-duty): $20 to $50.
Spending a little extra on a good base will save you from buying a new liner or a new pool next year. The base is the cheapest insurance you can buy for your pool.
Frequently Asked Questions
Can I Use A Tarp Instead Of Landscape Fabric?
Yes, but only if it is a heavy-duty woven tarp. Thin plastic tarps trap condensation and tear easily. Landscape fabric is the better choice because it allows water to drain through while blocking weeds.
How Much Sand Do I Need Under My Pool?
You need about one to two inches of sand. For a 15-foot round pool, this is roughly half a cubic yard of sand. The sand should be level and compacted, not loose and fluffy.
What Happens If I Put The Pool On Grass Without Anything?
The grass will die and rot. You will get a bad smell, an uneven surface, and a high risk of punctures. The pool liner may also develop mold. It is never a good idea to skip the base.
Is Foam Padding Better Than Sand?
Foam padding is easier to install and provides better insulation. It is also less messy than sand. However, sand is cheaper and can be shaped to fix minor leveling issues. Both are good options, so it comes down to your budget and preference.
Do I Need To Remove Grass Before Putting Down A Pool Pad?
Yes. You should always remove the grass before placing any base material. Even a foam pad will not stop the grass from dying and decomposing underneath. Removing the grass ensures a clean, stable surface.
Final Thoughts On Pool Base Preparation
Setting up an above ground pool takes effort, but the payoff is a clean, safe, and enjoyable swimming area. The time you spend leveling the ground and laying the protective layers is time well spent. It prevents headaches later, such as leaks, odors, and uneven water levels.
Remember the core principle: you want a smooth, soft, and level surface that is free from organic material. By using sand, landscape fabric, and a proper pool pad, you create a barrier that protects your liner and keeps the water clean. Do not rush this step. A little extra work now means many summers of trouble-free swimming.
So, when you ask yourself what to put under above ground pool on grass, think about the layers. Remove the grass, level the soil, add sand, lay fabric, and then set up the pool. This simple formula works for almost every pool type and will give you the best results. Your pool will thank you, and so will your feet when you step onto a smooth, clean bottom.