Voids under swimming pools and concrete slabs can lead to significant structural problems if not addressed promptly. These hollow spaces beneath the surface can weaken the integrity of the structure, causing cracks, settling, or even collapse in severe cases. Understanding how these voids form and how to fix them is crucial for homeowners and property managers. In this blog, we’ll explain what voids are, the various ways they form, and the best methods to repair them.
What Are Voids Under Swimming Pools and Concrete Slabs?
A void is essentially a hollow space beneath a concrete slab or swimming pool. When the soil beneath these structures shifts, erodes, or compacts unevenly, it can leave empty spaces where the ground no longer supports the concrete or pool. Over time, these unsupported sections can lead to cracks, sinking, or even structural failure.
In the context of swimming pools and concrete slabs, voids can cause aesthetic and functional damage, from pool liners wrinkling to foundations cracking. Addressing these voids promptly can prevent the problem from escalating and preserve the integrity of the structure.
How Do Voids Form?
Voids form for several reasons, many of which are environmental or due to the natural settling of the soil. Here are some of the most common causes:
- Soil Erosion
One of the most common reasons for voids forming under swimming pools and concrete slabs is soil erosion. Water is often the primary culprit. Rainwater, flooding, or poorly directed drainage can seep into the soil, gradually washing away fine particles beneath the surface. As the soil erodes, it leaves empty pockets under the slab or pool, resulting in voids. This is particularly common in areas with sandy or loose soils, where water flow can more easily remove material.
- Soil Settlement
Over time, the soil naturally settles due to the weight of the structure above it. If the soil was not compacted properly during the construction process, the ground may compress unevenly. This uneven settlement leads to gaps or hollow spaces beneath the slab or pool. As sections of the soil compress and shift, some areas may sink more than others, resulting in voids.
- Poor Drainage
Improper drainage around your home or pool can exacerbate void formation. When water isn’t properly diverted away from the foundation, it can saturate the soil and cause it to weaken or erode. This is particularly problematic in areas like Florida, where heavy rainfall can contribute to water pooling around the foundation or pool.
- Expansive Soils
Some soils, such as those rich in clay, are prone to expansion and contraction. When these soils get wet, they swell, and when they dry out, they shrink. This constant cycle of swelling and shrinking can create voids under concrete slabs and pools. Over time, this repeated movement weakens the soil’s ability to support the weight of the structure above.
- Burrowing Animals
Although less common, burrowing animals such as moles or rodents can also cause voids to form. These animals dig tunnels beneath the ground, which can eventually lead to unsupported sections of the soil under the slab or pool.
Signs of Voids Under Pools and Slabs
If you suspect there are voids under your swimming pool or concrete slab, here are some signs to watch for:
- Cracks in the slab: One of the most common indicators of voids is cracking in the concrete. These cracks often appear as a result of uneven pressure on the slab.
- Uneven surfaces: Voids can cause certain areas of the slab or pool deck to sink or settle unevenly, leading to sloped or sunken sections.
- Gaps between the pool and deck: If you notice a growing gap between the swimming pool and the surrounding deck, it could be due to a void beneath the surface.
- Tilting or shifting: In more severe cases, sections of the concrete slab or pool can tilt or shift as a result of void formation.
How to Fix Voids Under Swimming Pools and Concrete Slabs
Repairing voids under concrete slabs and swimming pools requires professional intervention to ensure the structure is stabilized and the underlying problem is corrected. Here’s a breakdown of the most common methods used to fix voids:
- Mudjacking (Slabjacking)
Mudjacking, also known as slabjacking, is a common method for filling voids beneath concrete slabs. It involves pumping a mixture of water, soil, and cement (called slurry) into the void through small holes drilled in the surface. This slurry fills the void and hardens, providing support to the concrete above. Mudjacking is a cost-effective solution and can be completed in a relatively short amount of time.
The steps typically include:
- Drilling small holes in the affected area of the slab.
- Pumping the slurry mixture into the void.
- Patching the holes once the void is filled.
While mudjacking is effective for filling smaller voids, it may not be as durable for larger or more severe cases where the soil condition is unstable.
- Polyurethane Foam Injection
Polyurethane foam injection is a more modern and efficient method of fixing voids. It involves injecting expanding polyurethane foam into the void, where it fills the space and then hardens to stabilize the slab or pool. This method has several advantages over mudjacking:
- The foam is lighter than slurry, which reduces the load on the soil.
- The material expands, allowing it to fill smaller and more complex voids.
- It hardens quickly, meaning the repair process is fast and minimally disruptive.
The process of polyurethane foam injection includes:
- Drilling small holes in the concrete.
- Injecting the foam into the void.
- Allowing the foam to expand and harden.
Polyurethane foam is an excellent option for voids under swimming pools, as it can support the structure without adding significant weight to the underlying soil.
- Compaction Grouting
Compaction grouting is another technique used to repair voids, especially when soil settlement is the issue. In this process, a grout mixture is injected into the ground, where it compacts the surrounding soil while filling the void. This method strengthens the soil and restores support to the overlying slab or pool.
- Soil Stabilization
In cases where expansive soils are causing the formation of voids, soil stabilization techniques may be necessary. These techniques involve injecting stabilizing agents, such as lime or cement, into the soil to reduce its ability to expand and contract.
Conclusion
Voids under swimming pools and concrete slabs can lead to serious structural issues if not addressed quickly. These hollow spaces form due to a variety of factors, including soil erosion, settlement, and poor drainage. Fortunately, several repair methods, including mudjacking, polyurethane foam injection, and compaction grouting, are available to stabilize the structure and prevent further damage. Regular inspections and prompt action are essential for maintaining the integrity of your pool or slab, ensuring a long-lasting, stable foundation.
