You have a slab foundation (at least you think you do) and you want to know more about what type of foundation you have. Like how are slab foundations made? What causes them to break or become damaged? And how can slab foundations be repaired? Are there different foundation repair methods? That kind of stuff.
Well, aren’t you awesome, lookin’ for more information about your home so you can understand it better . . . you get a gold star for homeownership today!
At Anchor Foundation Repair, we have inspected and repaired thousands of homes in the Bryan-College Station area for over 35 years. Knowing this kind of information is the “foundation” of our service and work for Brazos Valley homeowners. We share it with you in easy-to-understand, non-industry language through our learning center and personal contact.
In this article, we will cover some basic questions you have about your slab-on-grade foundation:
- What is a slab-on-grade foundation? How is it made?
- How does a slab foundation become damaged or crack?
- What repair methods are there for slab foundations? There are 6 of them.
Are you ready to “dig in” to the riveting world of slab-on-grade foundations? Let’s see what this slab stuff is all about.
A. What Is a Slab-On-Grade Foundation?
First things first, let’s make sure everyone knows what defines a slab-on-grade foundation by exploring the words. There’s the word “slab,” it’s not a slab of meat, it’s not a slab of marble, it’s a slab of concrete that is poured all at once.
What does “on-grade” mean? Good question. In the construction industry, “grade” is another word for ground. So the slab is poured on a prepared ground lot and there is no space between the ground and the slab. Not super sure why they didn’t just call it a “slab-on-ground” foundation but that might just be a mystery for the ages.
According to our Wiki-good friends, a slab-on-grade foundation is just one of five basic types of shallow foundations used in construction. It is considered a shallow foundation because it essentially “floats” on the soil surface without a great deal of deep underground support.
Knowing what these words mean only gets you halfway there to understanding this type of foundation. The rest of it comes from understanding how it’s made.
How Slab-on-Grade Foundations are Made
Conventional slab foundations are the most prevalent of all home foundation types in Texas today. Slab foundations have been around and widely used since the 1950s. So if your home was built in the last 60 years or so, it’s probably a conventional slab-on-grade foundation, or a slight variation called post-tension slab foundation is gaining in current building popularity.
Regular slab foundations can be most easily identified by the flat solid concrete piece that your home rests upon. You will see concrete near the ground on the outside perimeter of your home, you will feel concrete under the floors of your home. If you saw your home being constructed, you will see it as the footprint of your home on the ground shaped in concrete.
This type of foundation is made by pouring concrete all at one time directly onto specially prepared ground. The slabs are about 4 to 6” thick. A perimeter and grid of trenches are dug (looks a bit like an irregular waffle) to make the foundation. The concrete is reinforced with steel rebar throughout. A post-tension foundation uses a woven grid of cable instead of rebar.
The edges aka “beams” of the foundation are thicker (from 24 to 30” or more). The beams go deeper into the ground around the perimeter of the home, while interior support beams tend to be less deep than the perimeter beams.
Slab-on-grade foundations are very popular in warmer climates like we have here in Texas. They are not used in colder climates where the ground freezes regularly and for long periods like in the northern United States. Generally speaking, they are easier and cheaper to install and are preferred by home builders because of this.
B. How Does a Slab Foundation Become Damaged or Crack?
It seems like concrete would last forever, but alas it does not. Like anything else in this world, slab foundations can move, break, crack, or be damaged over time. Three main conditions lead to foundation settlement and damage to your home: expansive clay soil plus climate inconsistency, under-slab plumbing problems, and poor initial construction.
Our Special Soil + Our *Special* Climate
The combination of the properties of our local soils plus a climate with wet and dry extremes creates a special recipe for foundation damage. The two forces of expansive clay soils and inconsistent climate conditions work together and strongly impact your home foundation.
Expansive Clay Soil Properties
Throughout central Texas where we live, expansive clay soils dominate the landscape east of I-35. We could write a whole article just on this topic but in a nutshell, expansive soils expand and contract based on moisture levels.
The molecules in the soil puff up when wet and deflate when dry. The molecules are packed closely together and push out all the way around (like inflating a ball), but because they are tightly packed they can’t push out very well on the sides so they push up instead (where there is less resistance) and with much more power on your home’s foundation during rainy seasons.
Then when it’s dry, they sink down and retract to a smaller molecule size and let your foundation fall back. Repeat this pushing and falling effect over and over again through the years.
Your home’s foundation will begin to weaken and sometimes break due to these strong forces and then it moves from its original position. This is what we call “settlement” in the industry.
The forces of expansive clay soils on your home are like daylight savings time on your foundation, springing forward (up) and falling back every year.
Inconsistent Climate Conditions
Now combine expansive clay soil with our delightful weather patterns. Sometimes we get a lot of rain for extended periods, and then we will get no rain. Like none . . . for a long time . . . welcome to Texas!
Since our rainy and drought seasons tend to be *kind of intense* (to put it nicely), our soil is a bit like manic depression. Sometimes it’s strongly lifting and powerful: getting lots of stuff done messing around with your foundation. Sometimes it’s just feeling depressed and sadly sinking down. It’s enough to make any foundation in our area well . . . crack up a bit.
If it were dry here all the time, the expansive soils wouldn’t expand. If it were wet here all the time, the expansive soils would stay expanded.
If there were consistency in the climate, this wouldn’t be such a problem for your foundation but . . . all I can say again is . . . welcome to Texas: where “inconsistent climate conditions” is our three-part middle name!
Under-Slab Plumbing Problems Can Cause Foundation Damage
Leaks from plumbing lines under your home also contribute excess moisture to the expansive clay soil under your home. Remember what moisture does to our soil? If lines are leaking under your home over a prolonged period, it causes the soil to heave and pushes your slab up and it can move, crack, or break.
Leaking water under a home can cause poorly packed soil to “wash out” and create voids or empty space under the home. Voids lessen the support under the home and can cause a slab to crack or break as well.
Broken plumbing lines leaking water can also attract tree roots to the water and those roots are powerful damagers of both plumbing lines and foundations over time.
Time is the enemy with under-slab plumbing leaks. You can’t see them and have no idea how long they have been going on until you begin to see damage or problems caused by the leaks. The longer the plumbing lines leak, the more foundation movement or damage can happen.
Under-slab plumbing leaks are one of those, “Which comes first, the chicken or the egg?” situations where it’s hard to know what caused what first. Did the plumbing leak cause the foundation movement or did the foundation movement cause the plumbing leak? Either way, your foundation can be damaged and could need repair.
Plumbing issues are a big reason people can decide to quickly get their foundation repaired, rather than waiting.
Poor Initial Construction Methods Can Cause Foundation Problems
Poor construction can be a cause of foundation problems. We are listing it last here because it is not very common. There are some cases where poorly prepared grade (aka ground) can cause instability in the foundation.
Also, when mixing and pouring concrete builders have to watch the ingredient and temperature levels. If the concrete is not mixed properly or the ingredient proportions are off, it can affect the durability of the foundation. If it’s too cold or rainy when they pour the concrete for the foundation, that can weaken the material as well.
Instances of poor construction methods causing the foundation issue are rare but we want to acknowledge their existence in the spirit of thoroughness. We tend to have good builders and contractors in this area, but in larger metropolitan areas this could be a more prevalent issue.
Building codes help to establish minimum construction standards in most areas and will help ensure that homes are well built. But building codes have evolved and continue to change over time and something that was okay 40 years ago has a stricter code now.
So older homes might be more susceptible to construction method failures or rural homes may not have been subject to any building codes at all depending on how far outside of a municipality they are located. Just something to keep in mind in case your home is older and/or in the country.
C. What Repair Methods or Types Are There for Slab-On-Grade Foundations?
All slab-on-grade foundation repair methods have at least one thing in common. Each method will have a way of adding extra support under and around the home to bring it back to its original elevation. Even if the methods are very different, they at least have that in common.
There are surprisingly quite a few different methods of foundation repair that exist in the world. When you are choosing a foundation repair company, you are often also choosing a method of repair. Most foundation repair contractors will only specialize in one repair method, although you could find a rare contractor that does more than one.
It’s safe to say that you are never going to find one repair contractor that offers all methods or does all of the methods very well. Some of these methods may not even be available in your area at all. But we will tell you about each one briefly in order by primary repair material.
1. Steel Pressed Pilings
A steel piling is made up of stacked steel pipe pieces that are a little less than 3 inches in diameter and come in lengths of 1 to 3 feet. The sections of steel pipe are stacked on top of one another as they are driven into the ground using a hydraulic ram.
There is a variation of this method where concrete is poured into the center of the shaft pipe, but it is still considered to be steel pressed piling.
The number of steel sections needed depends on the soil conditions under your home. Steel piers can go to great depths (up to 100 feet if needed) and are good for installation in hard rock areas.
2. Steel Helical Piers
A helical pier is sort of an “earth anchoring device” that looks like a drill bit and is also known as a screw pier. The helical pier has one or more metal discs that are welded in a spiral pattern around a rigid central steel pipe.
They get their name from the spiral helix pattern (like you see in the double helix of human DNA). The spiraling pieces help distribute weight and anchor the pier into the ground.
Helical piers are used frequently in commercial building applications as well as areas with high groundwater levels. They are also used more in higher wind and/or seismic activity areas.
3. Concrete Pressed Pilings
Concrete pressed pilings aka pressed piles or friction piers are similar to the steel pressed pilings in that sections are driven by hydraulics into the ground. The concrete sections are cylindrical and measure 6” in diameter and 12” in length. Each section is pressed into the ground on top of one another until the ground pressure will not allow any more to be pressed.
There are variations of this method where a cable or rebar is inserted into the center of the concrete cylinders for extra support or the pile has a special base or cap, but the basic principle is the same. They are all reliant on the friction between the concrete and the clay soil to remain in place and functioning.
Concrete pressed piles are used frequently in residential foundation repair in the Central Texas area and are known for quick installation and lesser cost than other repair methods.
4. Drilled Concrete Piers
Each drilled concrete pier is made individually on-site for foundation repair, as opposed to the other methods so far that use premade materials that are pieced together on-site. Drilled and poured concrete piers can also be called bell-bottom piers due to the distinctive bell shape at the bottom of the shaft that resists soil uplift and increases anchoring stability.
A simple version of this type of pier is used in original construction for things like deck footings. A longer, more enhanced, and reinforced version of this type of pier is used in home and commercial foundation repair.
5. Hybrid Piling with Steel and Concrete
A pressed pile method that uses steel sections at the base of the pile and concrete cylinders near the top of the pile exists as well. This combination of two materials could be more of a marketing spin than a true engineering and performance-based solution. It is unclear if this hybrid method has any true advantages over either single material method.
6. High-Density Polyurethane Foam Injection
A method commonly called “polyjacking” is also used in foundation repair and flat surface concrete repair. A specialized polyurethane foam is injected by drilled holes through the top of the foundation. The foam puffs up and pushes your foundation back up to its intended elevation from below and then solidifies to hold your home in place.
This method is very different from the other methods because it does not use perimeter support around the edges of the home. It only fills voids and lifts from underneath the interior areas of the home. Even though the word foam sounds like something weak, this material has significant weight-bearing strength.
Polyjacking can also be combined “hybrid-style” with other exterior pier methods. This is an advantage as interior pier work can be messy. Using polyjacking on the interior combines the perimeter support strength of piers with the interior simplicity of foam.
What Slab-On-Grade Foundation Repair Methods are Available in this Area?
As we mentioned earlier, some of the slab-on-grade foundation repair methods may not even be available in your area at all. In the Brazos Valley area, there are locally-owned foundation repair contractors that do concrete pressed piles and poured concrete piers.
Out-of-town contractors willing to come to the Brazos Valley can do concrete pressed piles, hybrid steel/concrete piles, and high-density polyfoam injection. We are not aware of any steel pressed piling or helical pier contractors that commonly come to this area.
Remember that when you are choosing a foundation repair company, you are choosing a method of repair as well. We compiled information on other foundation repair contractors in our area if you are interested.
Well, What Method Does Anchor Foundation Repair Use?
Good question! Thanks for asking. Although both methods available in our area have merits and are good in certain situations, Anchor Foundation Repair uses only the drilled concrete bell-bottom pier method of foundation repair. We believe that it has some strong pro features vs. the pressed pile method of repair.
The biggest pro is that this method is the longest-lasting and most durable method of repair. Because of this durability, we offer a lifetime warranty and service agreement on our slab-on-grade foundation repair.
We have been doing business in this community for 35 years and counting and plan to be around for the long haul. We can make good on warranty work because we aren’t going anywhere. Good work takes time too. The bell-bottom pier system takes some time to install, check out this article about our method to see what timeframes to expect from this type of repair.