A fiberglass pool is a big investment, and homeowners naturally expect it to stay level and stable for decades. But sometimes, things don’t go as planned. We’ve worked with homeowners across the Kansas City area who have noticed their pool shifting or even floating, not just a cosmetic issue, but a structural concern that requires prompt attention. So, what causes pools to shift in the first place? In this post, we’ll break down the causes so you know what to look for and what to do next.
The Main Reasons Pools Shift or Float
Poor Backfill Material
The most common cause we see when a fiberglass pool shifts is improper backfilling. This is the material that fills the gap between the outside of the pool shell and the surrounding ground. When done right, it provides support and prevents movement. But if a builder cuts corners and uses dirt instead of clean gravel, the pool is more likely to settle unevenly or shift. Dirt holds moisture and compacts over time, which creates voids that the pool can sink into.
We always use clean, angular gravel, typically 110 to 150 tons, to ensure the pool shell remains supported. It’s more expensive than dirt, but it’s necessary to protect your investment.
Lack of Drainage and Hydrostatic Pressure
Pools are buried structures. When water builds up underneath them, it creates hydrostatic pressure that pushes upward. If the pressure gets too high and there’s nowhere for the water to go, it can cause the pool to float.
To stop this from happening, we install a hydrostatic pressure relief valve under every fiberglass pool we build. Think of it like a sump pump under your house; it relieves pressure and redirects water safely away. Without this valve, even a heavy fiberglass pool can rise out of the ground when the water table gets too high.
What Causes Pools to Shift During Heavy Rain?
After a heavy rain, the ground around your pool becomes saturated. If the backfill isn’t free-draining gravel or if there’s no proper relief for water under the pool, the pressure builds fast. This can lead to a shifted or bulging pool wall, uneven waterlines, or cracks in the decking. This is why both the right material and drainage strategy are essential.
Signs Your Pool Might Be Moving
Uneven Waterlines
One easy way to check for movement is to stand back and look at the waterline. Water will always find its level. If one side of the water is noticeably higher than the other, your pool may have shifted.
Cracking Around the Deck or Pool
Cracks in the pool decking or separation between the pool and the surrounding concrete can also signal shifting. These signs usually mean the ground beneath has moved or settled.
Bulging Pool Walls
A bulge in the wall of a fiberglass pool is often due to pressure from saturated soil. If the surrounding ground holds moisture, especially if it was backfilled with dirt, it can push against the pool structure.
How We Prevent Pool Shifting at Hinkle
At Hinkle Outdoor Living, we follow strict installation practices that are designed to prevent these problems from the start. Here’s what we do differently:
- Use only clean, compacted gravel as backfill, never dirt
- Install hydrostatic relief valves to control underground water pressure
- Ensure proper drainage grading around the pool perimeter
- Carefully inspect site conditions before digging
- Remove excess soil from the site rather than cutting corners
These steps may add time and cost up front, but they prevent much bigger repair bills down the road.
Key Takeaways for Homeowners
- What causes the pools to shift is usually poor backfill material or unmanaged underground water pressure.
- Never backfill a fiberglass pool with dirt. Use clean gravel to avoid future settling.
- Install a hydrostatic pressure relief valve to keep water pressure from lifting the pool.
- Look for signs like uneven waterlines, cracked decking, or bulging walls to catch problems early.
- A professional pool installer like Hinkle will always follow best practices to ensure a long-lasting pool installation.
Ready to Get Started?
If you’re considering a new fiberglass pool or worried about movement in your current one, our team at Hinkle Outdoor Living is here to help. We’ll inspect your site, explain the right installation process, and make sure your pool is built to stay put. Contact us today to schedule a consultation.
