So, you’ve decided to install an above ground pool. That’s exciting! But before you start filling it with water, you need to figure out what to put under above ground pool on grass. Getting this foundation right is the single most important step for a safe, stable, and long-lasting pool. A poor base leads to lumps, bumps, leaning walls, and a very short pool lifespan.
This guide will walk you through every option, from the simplest to the most professional. We’ll cover the materials, the step-by-step process, and the common mistakes to avoid. Your goal is a perfectly level, stable foundation that protects your pool liner and provides years of trouble-free fun.
What To Put Under Above Ground Pool On Grass
You can’t just plop your pool on the lawn and hope for the best. Grass and soil are living, shifting surfaces. Weight and moisture will cause settling and unevenness. The right foundation materials distribute the pool’s weight, block weeds, and cushion the liner.
Here are the most common materials used, from the ground up.
Ground Contact Layer (The Weed & Moisture Barrier):
This is your first layer, directly on the soil.
* Geotextile Fabric (Ground Cloth): This is the professional choice. It’s a tough, permeable fabric that stops weeds and pests but allows water to drain through. It prevents erosion under your sand layer.
* Heavy-Duty Landscape Fabric: A good alternative, though sometimes not as thick as commercial geotextile. Avoid the thin, cheap stuff—it will tear.
Pool Pads: These are often foam or felt sheets sold specifically for pools. They provide cushioning but should usually go over your sand base, not directly on soil, for best stability.
The Leveling & Cushioning Layer:
This is the main layer that creates your flat, supportive surface.
* Mason Sand (Builder’s Sand): This is the gold standard. It’s coarse, washed, and compacts well. You’ll want a 2-3 inch layer, perfectly leveled. Do not use play sand or fine “beach” sand—it washes away and shifts too easily.
* Stone Dust (Crusher Fine): A very stable, compactable material that creates an almost concrete-like base when leveled and tamped. Excellent for stability, but must be leveled perfectly smooth to protect the liner.
* Crushed Stone/Gravel: Sometimes used as a sub-base for very soft ground before adding sand. It provides drainage but is not a top layer—you’d still put sand over it.
The Final Protective Layer:
This goes directly under the pool liner.
* Commercial Pool Floor Pad: A thick, felted or foam pad that provides ultimate cushioning and protection from tiny stones or roots. It’s a great investment.
* Solid Foam Insulation Boards (XPS, not EPS): Taped together seams, these create a perfectly smooth, insulating floor. It’s like having a concrete floor without the cost. Must be covered with a tarp or pool pad to protect from UV rays.
* Old Carpet (A Temporary Fix): Some folks use clean, padding-free indoor/outdoor carpet. It can work short-term but can rot, hold moisture, and attract insects. It’s not recommended for a permanent setup.
Why a Proper Base is Non-Negotiable
Skipping a proper base is the biggest mistake you can make. An uneven foundation puts immense stress on the pool walls. This can cause seams to fail, the wall to buckle, or the top rails to collapse—especially when the pool is full. That’s thousands of gallons of water rushing out.
A good base also makes the pool floor comfortable to walk on and prevents grass and weeds from decomposing and creating methane gas bubbles under your liner. Trust me, you don’t want those.
Step-by-Step: Preparing the Perfect Foundation
Follow these steps carefully. Rushing here will haunt you all season.
Step 1: Choose and Mark Your Location
Pick a spot that is:
* Perfectly level (even a 1-inch slope across a 24-foot pool is a problem).
* Away from overhead power lines and trees (roots and falling debris).
* On stable soil, not fill dirt or a recent compost pile.
* Clear of underground utilities.
Mark the area using stakes and string. Make the circle or oval 12 inches larger than your pool’s diameter on all sides. This gives you room to work.
Step 2: Clear and Kill the Grass
You must remove all organic material.
* Option A (Thorough): Use a sod cutter to remove the top layer of grass and roots. This is the best method.
* Option B (Effective): Spray the marked area with a non-persistent grass killer. Once the grass is dead, you can till it into the soil, but removing it is cleaner.
Step 3: Excavate the High Side to Level
This is the most labor-intensive part. Do not build up the low side with fill—it will settle.
1. Use a long, straight 2×4 with a carpenter’s level on top to find your high point.
2. From that high point, excavate the entire area down to the lowest point. Your goal is virgin, undisturbed soil that is perfectly level.
3. Check for level in multiple directions, like spokes on a wheel. A laser level is a huge help here.
Step 4: Compact the Soil
Use a hand tamper or a mechanical plate compactor on the exposed soil. This creates a firm, unyielding starting layer. Walk over it—if you leave deep footprints, it’s not compacted enough.
Step 5: Add Your Base Material (Sand or Stone Dust)
If using a stone sub-base for drainage, add and compact that first.
1. Spread your mason sand or stone dust evenly across the area.
2. Aim for a 2-3 inch depth after compacting.
3. Use a screed (a long straight board) to pull and level the sand. This is like frosting a giant cake.
4. Lightly mist the sand with water and use the plate compactor. This is crucial—it locks the sand in place so it won’t wash out.
Step 6: Lay Your Ground Barrier
Roll out your geotextile fabric or heavy-duty landscape fabric over the compacted sand. Overlap seams by at least 6 inches. This layer now separates your sand from your protective top layers.
Step 7: Add Your Final Protective Layer
Now install your pool floor pad or foam boards.
* For foam boards, cut them to fit tightly, tape the seams with waterproof tape, and cover them with a final cover (like a non-woven pool pad) to protect from sun and feet.
* For a pool pad, simply roll it out and trim it to fit.
Common Materials to Avoid on Grass
Some things seem like a good idea but will cause problems.
Just a Tarp Alone: A tarp directly on sand or soil creates moisture pockets, promotes mildew, and offers zero cushioning. It can also become slippery. Always use proper materials under the tarp.
* Cardboard or Newspaper: They biodegrade quickly, creating voids and an uneven base. They also attract insects.
* Play Sand: Too fine, it shifts and washes away, creating hollow spots.
* Only Soil or Dirt: It will never be perfectly level, compacts unevenly, and grows weeds directly into your pool floor.
* Wood Chips or Bark Mulch: These decompose and shift constantly. They are not stable at all.
What About Using Just a Pool Pad on Grass?
It’s tempting to skip the hard work and just lay a cushy pool pad on the grass. This is a major risk. While the pad protects the liner, the soft, uneven ground beneath will still settle. Your pool will become unlevel, putting all that weight on one section of the wall. I’ve seen pools fail from this. The pad is a top layer, not a foundation solution.
Maintaining Your Foundation Over Time
Your job isn’t done after installation.
* Check for Level: At the start of each season, use a level on the top rails in several spots. Note any changes.
* Look for Settling: After heavy rains, walk around the pool perimeter. Feel for soft spots or visible dips under the pool wall.
Manage Water Drainage: Ensure rainwater and splash-out runs away from the pool base. Consider a French drain or swale if you have persistent water pooling nearby.
* Address Weeds Immediately: If you see a weed poke through the side, remove it carefully and patch your ground cloth.
A little annual check-up can prevent a catastrophic failure mid-summer.
Special Case: Temporary Seasonal Setups
If you truly only put the pool up for a few months and take it down, you can use a slightly simpler method. But stability is still key.
1. Mow the grass as short as possible.
2. Lay a thick, commercial-grade geotextile fabric directly on the grass.
3. Add 1-2 inches of mason sand on top, level it carefully.
4. Use a solid pool floor pad or interlocking foam tiles as your final layer.
This method is better than nothing, but expect some settling and plan to relevel the site if you reuse it.
FAQ Section
Q: Can I put an above ground pool directly on grass?
A: No, you should never place the pool liner directly on grass. Grass will die, decompose, and create a lumpy, smelly mess that damages the liner and destabilizes the pool. Always use a proper base system.
Q: What is the cheapest way to prepare the ground?
A: The most cost-effective reliable method is to remove the sod, level the soil, and use a 2-3 inch layer of mason sand over landscape fabric. Don’t cheap out by skipping steps—it will cost you more in liner replacements or pool failure.
Q: How level does the ground need to be?
A: Extremely level. The industry standard is within 1 inch across the entire diameter. Even a small slope creates dangerous pressure differentials on the pool wall. Take your time with this step.
Q: Can I use foam boards instead of sand?
A: Yes, extruded polystyrene (XPS) foam boards are an excellent option. They go over a level base of sand or stone dust. They provide a smooth, insulating floor but must be covered to protect them from punctures and sunlight.
Q: Do I need to put something under my above ground pool legs?
A: Absolutely. Pool legs can sink into soft ground. Use large, solid patio pavers or concrete blocks placed flush with the ground level under each leg. This distributes the weight and prevents sinking.
Q: How thick should the sand base be?
A: A compacted layer of 2 to 3 inches is ideal. Thicker than 3 inches can become unstable and shift over time if not properly contained.
Getting the foundation right requires effort upfront, but it pays off every single day you use your pool. You’ll have peace of mind knowing your pool is stable and safe. The smooth floor will be gentle on your feet, and your liner will last for seasons to come. Take a weekend, do the job properly, and then enjoy the cool, refreshing reward all summer long. There’s nothing better than knowing you built it right.