Slab foundations are a simple, cost-effective foundation type that allows a house to be supported by a simple concrete slab. There are many advantages to having a slab foundation, but no matter how convenient they can be, like other foundation types, they can also settle.
The concrete slab that holds up your home rests upon a layer of soil. If that soil becomes displaced in any way, your home will no longer have an even foundation. A gap will form between the soil and the slab itself, and if enough weight is placed on the slab, it will begin to sink against the displaced soil. Concrete slabs traditionally sit upon a layer of gravel to help with drainage, but even the gravel can shift about once the soil underneath gives way.
Soil displacement occurs due to several reasons. Excessive rain and extreme weather are the two most common factors, especially in places like Huntsville, Alabama, and Chattanooga, Tennessee. Alabama is the third state in the contiguous U.S. with the most annual precipitation. Hurricanes are frequent in this state, so the flooding and severe winds displace the topsoil on homeowners’ properties bit by bit every single year. This makes it easier for water to reach under the house and displace the soil there.
It’s the same story with homes in Tennessee, which is at the heart of Dixie Alley. The constant tornadoes and ice storms frequently disrupt the soil on any uncovered property.
Alabama and Tennessee may not be the coldest places in the United States, but they still see freezing temperatures during the winter. Because of the freeze-thaw effect, not only does soil become looser and less stable, the actual concrete slab itself gets damaged and loses its strength.
Slab Piers: The Solution for Settling Slab Foundations
To the layman, a cracked, settling slab foundation may seem impossible to repair. Luckily, we have reached a point in civil engineering where even the most severe structural issues have durable, reliable repair solutions. One such solution for slab foundations is the installation of slab piers.
Slab piers are rods made of solid steel that are meant to support the foundation. A settling foundation can no longer rely on soil to hold it up, so it needs another kind of support system that can bear the weight of the entire structure. Slab piers lift the slab back up and transfer the weight to the load-bearing soil below. Soil layers a few feet into the ground are a lot tougher and denser than topsoil, so they can support large weights. These underground soil layers are undisturbed and don’t get affected by weather conditions and are below the frost line, so they don’t get affected by the freeze-thaw effect either.
Part of the reason slab piers are such great solutions for settling slab foundations is because no matter how much the above soil layers get displaced, the stable soil will keep supporting the house. It’s a permanent solution that prevents settling for the rest of the house’s lifespan.
How Slab Piers Are Installed
The process for installing slab piers is incredibly easy and non-invasive. There are two kinds of slab pier systems that can be installed: helical slab piers and push slab piers. Depending on the kind of pier system required for your foundation, there might be a few variations, but everything can be done in less than a day depending on the size of the house and how many piers need to be installed.
Push Slab Pier Installation
The weight of the house is transferred to the piers. During this part, the slab will begin to level out and become even again. Once this is done, a mixture of water, cement, and sand is pumped underneath the slab to fill the gap left behind by soil displacement. The holes that were drilled are covered up with cement and the job is done.
Before installation, contractors will inspect the settling foundation to determine where the piers will be placed. A hole is drilled through the concrete slab and a bracket is placed so the flanges are on the underside of the slab. The steel piers are hydraulically pushed through the hole until reaching the required soil depth.
Helical Slab Pier Installation
The installation process for helical slab piers is extremely similar to push slab piers. After inspection, holes are drilled where the piers are to be installed. Before the bracket is installed, the pier itself is slowly drilled into the ground with a machine until it reaches the proper soil depths. The torque indicates how much weight the pier will be able to bear as it’s being drilled down.
The bracket is positioned underneath the slab and the weight of the foundation is transferred to the soil below. The grout is pumped under the slab and the holes are filled and covered.
The Difference Between Helical Slab Foundations and Push Slab Foundations
Although their installation process is similar, helical slab piers and push slab piers serve contrasting functions. The kind of slab pier you get to repair your settling foundation will depend on what your contractor says you need for your particular case. Let’s look at the differences:
Push Slab Piers
Push piers are hollow rods that rely on the weight of the home to create the resistance needed to work properly. The piers are pushed in with a hydraulic ram until they cannot be pushed any further. The weight of the house is what acts as the counterweight needed to keep the piers at load-bearing depth.
Because push piers are inserted into the ground with a hydraulic ram, they are able to penetrate through bedrock and tougher soils better. Push piers cannot be removed once they are put into place, so if the house is to be expanded in the future, the workers won’t be able to remove the piers.
Because of this, push slab piers are good for:
- Big, heavy homes
- Properties surrounded by bedrock
- Homes that won’t have expansions
Helical Slab Piers
Helical piers are steel shafts that have helix blades welded to the bottom of the shaft. They rely on load-bearing soil to support the foundation. If the load-bearing soil is found at a depth that the pier cannot reach, contractors can simply add more shafts to the piers to lengthen them. They have impressive load-bearing capacities, but not as much as push piers, which is why it’s so important that they reach competent soil to support the foundation.
Unlike push piers, helical slab piers can be removed. Because of this, helical slab piers are good for:
- Properties with soft soils
- Smaller homes
- Homes that will be remodeled or expanded
How Do I Know If My Slab Foundation Is Settling?
When a home’s foundation begins to settle, it affects the entire house. Without a stable foundation, the walls, the roof, and the chimney will begin to fall apart. Some problem signs of foundation settling are very subtle, but they get worse over time, so keep a lookout for the following so you can spot the problem early:
- Cracked walls and ceiling
- Cracked pillars
- Uneven floors
- Jammed windows and doors
- Floor leaking
- Frequent plumbing issues
- Broken kitchen and bathroom tiles
- Uneven home
- Tilting chimney
- Cracks at the bottom of the house
Slab foundation settling is one of the most disruptive problems a home can face. If the house had a basement or crawl space, the most severe damage occurs outside of the homeowner’s regular living space. However, because homes with slab foundations don’t have a sub-level that can take the brunt of settling damage, the entire house is affected quickly. This means that many repairs will have to be done by the time you notice the settling. If you experience any of the above problem signs, contact your local foundation experts as soon as possible to avoid further settling and further damage.
Do I Have To Replace My Foundation If It’s Cracked?
When a concrete slab foundation sinks, there is always a chance that it cracks as the weight of the entire house is distributed unevenly. Once it cracks, leaking and flooding will be a common occurrence, floors will begin to sink, and the pipework and ductwork system under your home will be damaged.
The idea of using slab piers to raise a settled slab foundation might sound good, but does it work if the slab is cracked? Wouldn’t it be easier to simply replace the foundation entirely?
Replacing your foundation is an arduous, long, costly process that is short-lived, and doesn’t address the problem at hand. When a slab foundation is replaced, it still rests upon soil. Sure, this soil may be newly placed, but if the previous soil eroded, there is nothing stopping this new layer to erode eventually. The new slab will settle again in a few years, rendering the replacement job useless.
Not to mention, you will have to move out of your house for weeks while the foundation is in the process of being replaced. The pipes and ductwork under your slab will have to be uninstalled and reinstalled, which will cost a lot of money.
When using slab piers, the foundation does not rely on the soil to stay stable. Because of this, they are a much more reliable and long-term solution to foundation settling. Even if the slab is cracked, slab piers can be used. They can even lift the cracked slab back into place so the contractors can seal and unify the two parts back together.
Slab Piers vs. Mud Jacking
If you are in desperate need of a contractor to fix your settling slab, while doing your research, you may have come across the term mud jacking for foundation repair. Mud jacking, also called slab jacking, is a concrete lifting method that has been around for many years. It involves drilling a hole in the slab and pumping in a slurry of cement. The cement is supposed to lift the slab until it’s even again.
Many contractors use this method, and it may seem like a cost-effective way of repairing your foundation, but it isn’t. This is because of the way the cement interacts with the soil.
First of all, cement is rough and heavy. Substantial amounts of pressure compact soil and causes further displacement. The cement is pumped right under the slab but right above the soil. If the soil underneath erodes away, the cement will settle against the soil just like the slab did.
Cement is permeable and can absorb water. Like most porous materials, concrete will erode as water and ice displace the particles. It will weaken with time and will fail to hold up the foundation as it once did in time. So, as you can see, mud jacking may seem like a workable solution at the time because of the attractive rates, but it’s a short-term fix that will end up costing you money in the future.
Whether the contractor is using helical slab piers or push slab piers, the machinery used to install them is small. This means that the piers can be installed in small spaces and the job can be completed from places like bathrooms and closets. This isn’t possible with mud jacking, since the machines involved are a lot larger.
Can I Install Slab Piers Myself?
When looking to get slab piers for your foundation, the most important thing is finding the right expert to do the job. There’s a lot of things to take into consideration when installing slab piers, and these are only things you can know if you are professionally trained and experienced in the job.
The soil needs to be tested and the slab needs to be inspected to know the kind of pier system you need. You would also need to load test the piers and know how to operate the machinery to get them to proper soil depths. Knowing where to drill and how many piers to install is crucial since drilling in the wrong place can harm the already debilitated slab. Overall, slab piers work best when installed by somebody who knows what they are doing.
Alabama and Tennessee may not be the coldest states in the country, but they do see below-freezing temperatures during the winter, even if only shortly. This means that slab foundations and the soil underneath are vulnerable to the freeze-thaw effect, which contributes to settling.
What It Is
The freeze-thaw effect refers to the cycle water goes through as it freezes and thaws during the winter. When water turns into ice, it expands by nine percent. This freezing and expansion can occur in any amount of moisture that is exposed to freezing temperature, including in the soil.
There is a certain depth at which water does not go through a freeze-thaw cycle, and the point where this no longer happens is called the frost line. In most of Alabama, the frost line can be found six inches into the ground. In Tennessee, it’s 12 inches down.
How It Affects Your Foundation
The soil that is under your home can be heavily affected by freeze-thaw. The soil is saturated by moisture from the snow during the winter, and once the temperature gets cold enough, usually at night, the water freezes and expands. The ice eventually thaws during the day, and the cycle continues. Because of the ice expansion, the soil particles get displaced, becoming looser, less stable, and more likely to allow water to saturate the deeper soil layers.
As for your actual slab foundation, this also gets affected. Concrete is a permeable material, so it will also get saturated with water. It may not seem like it, but expanding ice can go past concrete’s tensile limits and displace its particles. Over the years, the slab experiences micro-tears because of the freeze-thaw cycle that debilitates the concrete and makes it less likely to handle pressure.
Most concrete slab foundations are four to six inches tall. Although it would be preferable for a slab foundation to be reinforced with rebar, most aren’t. Does this affect the way the slab settles? It does, but not as much as you would think.
How It Helps
Concrete has amazing compression strength but terrible tensile strength. This means that it does not lose its volume when supporting a heavy weight, but if the pressure becomes too much, it will break apart. Concrete is especially vulnerable to substantial amounts of pressure that focuses on one spot and is not evenly distributed throughout the slab, which is why concrete breaks so easily when hit with a hammer.
Rebar is meant to increase the tensile strength of concrete, which is why it’s called reinforced concrete. What makes a slab crack when a house is settling is its inability to support the weight of the home as the foundation tilts and the pressure of this weight is focused on one side. With rebar in place, the slab would be able to handle more pressure, making cracks a lot less likely.
How It Doesn’t Help
Rebar may help a slab handle pressure, but it doesn’t stop the slab from settling. Even if the slab does not crack, the house will still sink because settling has to do with the soil under the house, not with the slab itself. Your home will still experience most of the structural damage that comes with settling, such as cracked walls and jammed doors, even with reinforced concrete.
This is why replacing the slab with one that has rebar is a wasted effort. The only way to truly stop settling is to allow the slab to be supported by something other than the soil underneath. This can be achieved with polyurethane foam injections or with slab piers.
You now know of helical slab piers and push slab piers, but are those the only viable options for a settling concrete slab? At AFS, we always make sure to provide homeowners with the best tools for their specific cases. Sometimes, a home’s slab foundation requires another kind of support system to combat settling. If needed, we can provide homeowners with another great concrete lifting method in the form of polyurethane injections.
How It Works
Polyurethane injections are a modern, innovative solution for slab settling. Here’s how it works: Contractors drill multiple holes where the slab needs to be lifted. Polyurethane foam is injected under the concrete, where it will expand and fill the gap until there is enough foam to lift the concrete and make it even again. The holes are covered up and the foundation is left looking like new.
Much like slab pier installations, polyurethane foam injections don’t require heavy machinery, so the job can be done in small spaces. The holes drilled are the size of a penny, so they will not harm slabs that are already severely damaged. It’s a fast, convenient process that also permanently solves the issue caused by displaced soil.
Why It Works
Polyurethane injections work because, like slab piers, they allow the foundation to rely on something other than soil for support. Polyurethane foam is tough enough to support over 100 tons of concrete. At the same time, it’s light enough to not compress the soil below and cause further displacement.
Polyurethane foam is also impermeable, so there’s no way water can pass through and saturate the soil. It serves as a barrier that keeps the soil dry and stable much better than the cement from mud jacking can. It is not affected by the freeze-thaw effect, so it’s a long-term solution for a settling slab.
Call AFS for Slab Foundation Repairs
If you are looking to install slab piers to stabilize your settling foundation, look no further. We specialize in all kinds of foundation repair and can provide you with the best repair methods in the industry. Don’t hesitate to call us or use our online contact form so we can schedule a free inspection. Our field experts will provide you with a quote as well as a rundown of what it’s needed and in what time it can all be done. Foundation settling is a headache, but it’s always our goal to make the repair process as seamless as possible.
We are proud to serve Birmingham, Huntsville, and Mobile, Alabama, as well as Nashville, Chattanooga, and Knoxville, Tennessee.