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Concrete Slab Lifting and Leveling

If you own a concrete pool deck or patio, you may be familiar with the fact that concrete slabs can sink. Yes, RenuKrete can help lift and level concrete slabs. Before we discuss how we level slabs, though, lets take a look at why concrete slabs sink to begin with!

While concrete is a very strong material, it is also very heavy and requires a very solid base underneath to support it. Usually, the base underneath concrete slabs of pool decks, patios - and even driveways and sidewalks - is compacted gravel on top of soil. When a concrete slab is sinking, its not really the fault of the concrete. The cause is always a problem with the base underneath the slab.

Top Reasons Why Concrete Slabs Sink

 

The top reasons why concrete slabs sink all have to do with the quality of the base underneath the slab. Maybe this base was not properly built by a contractor of owner who used too little gravel. By making the gravel layer too thin, the slab is not supported enough against the possible movements of the soil.

Just as important for a proper concrete slab support base is that the soil and gravel layer is properly compacted. Unfortunately, sometimes during the rush of a construction project, some contractors fail to compact the soil and gravel layer properly. This is especially problematic around in-ground swimming pools which require the back-filling of soil material behind the pool wall. This back-filling results in relatively loose material which is incapable of supporting a concrete slab. The soil needs to be compacted several times, then topped with gravel which also needs to be compacted several times. This is a time-consuming process, especially because the proximity of the pool wall makes aggressive compacting with heavy machinery risky. Too much downward force on the soil or gravel base - and maybe too close to the pool wall - could result in damage to the wall. Frequently, top contractors decide to leave days or weeks in-between compacting sessions. This, however, is very time consuming and costly. Some contractors end up taking short cuts and start pouring concrete on top of this sub-optimal base too soon. 

Over time, the base gives in to the heavy concrete and causes the slab to sink.

Typical pool deck with partially sunken slab.

Why a Sunken Concrete Slab Can Pose A Safety Hazard

Unfortunately, even properly poured and supported slabs can sink over time. This is because the support base can change. One typical reason is the impact of water in the soil. Even a small opening next to the slab, allowing rain water to wash out a section of soil over time can cause a slab to sink. Other times, ground water levels or ground water stream routes change, washing away supporting soil. The result can be a sunken slab that may be missing more than a bit of soil under it. It may be missing so much support base that is actually a risk to anyone setting foot on it! Take a look at this slab. It looked like "just another" sunken concrete slab. However, closer inspection revealed that several cubic yard of soil were "missing" - probably washed away by rain and ground water over time. Clearly, this was a severe safety hazard to the owner and their visitors. And the only indication from the top was that the slab was sunk by about 3/4" on one side.

Pool deck with significant safety hazard due to washed out support base under slab. Discovered during lifting attempt.

Other Reasons why Concrete Slabs Sink

As we mentioned before, when concrete slabs sink, it is because the ground underneath the slab is either not built right, or because it has changed. Especially in cold climates, in areas with clay soil, and in areas with high water tables there is a tendency for the soil underneath the slab to shift and give in. Ever heard of sink holes that all of a sudden open up in Florida? Many small (and not so small) changes take place underneath a building without us even knowing.

For this reason, the larger the building the deeper the support structure is anchored in the ground. This may be concrete footings that are driven or poured 4 feet deep for a small residential building. The foundation of the Empire State building is almost 50 feet deep, and the foundation of modern skyscrapers are driven even deeper. Nobody would want to see a skyscraper sink!

Frequently, we see concrete slabs sink when they are poured on top or on the side of a small hill. This doesn't have to be a big hill, just a few feet high. Typically, the pouring of a concrete slab requires a retaining wall to be built so that the soil on the upper part of the hill does not shift downwards. If it does, it takes the slab with it. Usually, this happens very slowly over the course of many years, by just a fraction of an inch per year. After a few years, though, it is enough to be a nuisance. Even worse, the opening that is created on the top by the moving slab allows rain water to penetrate underneath the slab and may wash out more soil - exasperating the problem.

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Typical pool deck with sunken slab. Water had washed underneath slab through loose pavers, compromising structural integrity of support base.

Pool deck that was built on hill. The retaining wall gave in after ten years and allowed the soil to give in underneath the slab. Water penetrating gap between slab and coping exasperated the problem.

RenuKrete Concrete Lifting​ and Leveling Can Help

If you have an issue with a concrete slab that has sunk, RenuKrete can help. Our proprietary technology has been developed to attack the root of the problem: the support base underneath the slab. 

By filling the void underneath the slab and creating upward pressure, the slab is lifted and brought back to its original position. So, concrete lifting and leveling are related and the usually accomplish a similar result: a level concrete slab. Cracks that were caused by the sinking slab can be repaired through the RenuKrete process, if needed.

 

So, whether your concrete slab is located around an in-ground swimming pool, in a walkway, patio or driveway, RenuKrete can help. Consider our concrete lifting and leveling services. Take a look at some of our completed projects and customer testimonials - then give us a call at 800-406-5010 to discuss your project and if RenuKrete is a good fit for you.

Concrete Pool Decks after RenuKrete Concrete Lifting and ECF Installation. 

Both of these locations had cracks before