Whether you have a new home or one built years ago, it’s scary to find a crack in a concrete slab foundation. If it’s a hairline crack, you may have nothing to worry about. If your slab foundation crack is getting bigger or if one side is raised, it may be time to call a structural engineer. Cracks occur for many reasons and often stem from multiple causes.
Three Reasons Concrete Slabs Crack
Cracks in concrete slabs fall into three categories: drying shrinkage, plastic shrinkage, and structural.
1. Cracks Caused by Drying Shrinkage
As poured concrete hardens, moisture evaporates from the slab, especially if the mixture was too wet. This problem can be prevented by using less water in the mix. Using too much water makes the concrete easier to manage, but it also makes it weaker.
2. Cracks Caused by Plastic Shrinkage
When concrete is wet, it is in a “plastic” state and stays that way for several hours. If moisture from the surface evaporates too quickly, especially during windy or hot weather, the concrete shrinks and cracks. Synthetic fibers or chemicals can be added to the mixture to help prevent shrinkage, but the cracks in cured concrete are permanent.
3. Cracks Caused by Structural Problems
Structural cracks usually occur when concrete is compressed from the side or when too much weight falls onto a single area. If the dirt under the slab settles unevenly, it can cause the slab to bend and cause slab foundation crack. A leaking water pipe that washes away soil and causes wet spots under or around a concrete slab foundation is another cause of cracking.
Structural cracks in new construction can be prevented by properly compacting the soil and gravel beneath the slab. Rebar, or steel reinforcing rods, can be added around the perimeter to offer additional support, but it is usually unnecessary in houses.
Slab Foundation Problems in Existing Homes
Even well-built homes can develop cracks, and the environment often plays a role. To keep structural damage from getting worse, ask for a foundation inspection as soon as you see these warning signs:
- Frequent rains that cause repeated soaking and drying
- Damage from tree roots that grow into concrete slabs
- Natural settling of foundation over time
- Erosion of topsoil
- Shoddy construction
- Improper grading
- Poor drainage
- Damage from the environment or natural disasters
Pier and Beam Foundation vs Concrete Slab Foundation
In many areas of the country, builders can choose between a pier and beam foundation and a concrete slab foundation. Each has its advantages and disadvantages.
A pier and beam foundation uses piers and beams to support a building. Piers are placed on rocks deep in the earth, and they support the beams that hold up the walls. This type of foundation is less likely to shift when the soil underneath moves. It allows contractors to make slight adjustments, but it is more expensive than a concrete slab foundation.
A concrete slab foundation sits directly on the soil beneath your home. Slabs work well on flat land, are easier to construct, and cost less than pier and beam foundations. Over time, concrete may be more expensive to maintain and repair than pier and beam foundations.
Slab Foundation Repair
Nobody wants to know their home needs concrete foundation repairs, but procrastinating only makes matters worse. The severity of problems varies. Some are easy to fix, and you may be able to do some repairs yourself. Others are more difficult and require the services of skilled professionals. Here are the nine most common repairs:
1. Sealants and Patches
If you have cracks caused by shrinkage, patches and sealants may be the best option. This type of crack rarely poses a structural threat, but it needs to be fixed to prevent further damage. Sealants and patches act like mortar to fill cracks and stop leaks. Shrinking problems usually occur in the corners of the foundation.
2. Foam Jacking
High-density foam jacking is one of the fastest and most economical ways to fix a foundation that is sinking or settling. Workers drill holes in the concrete and inject polyethylene foam underneath the slab. The foam expands and immediately fills in holes and raises the slab. You will need to check your plumbing afterward because the foam can enter pipes and harden, damaging plumbing.
3. Mudjacking
Mudjacking, also known as slabjacking, is used to repair concrete that has been poured on improperly compacted soil. The contractor raises the slab by drilling holes and filling them with a grout-like substance. Mudjacking can be done in all kinds of climates, only takes a few hours, requires nothing to be moved off the concrete, and doesn’t mess up the landscape.
4. Epoxy
Epoxy works like a sealant, but it’s also effective for repairing severe cracks. It can be injected or poured, making it a flexible solution to a difficult problem.
5. Pilings and Piers
Piles foundations are typically used in coastal areas to support shifting soil. Pilings are embedded several feet into the ground to keep the foundation from moving. Pilings, made of steel, are usually manufactured elsewhere and transported to the building site. Piers are constructed on-site from wood, steel and concrete. Although pilings and piers are more expensive than concrete slabs, they work better and last longer.
6. Water Management
Poor water management is second only to unstable soil as a major cause of structural damage. When a slab repeatedly soaks up water and then dries out, it puts the entire foundation at risk. Upgrades, such as installing water pumps and insulating crawl spaces, can prevent future problems.
The Takeaway
Budget and location are important factors when choosing a concrete slab foundation. A slab is more durable and affordable than a pier and beam foundation. It dries quickly and doesn’t delay construction. Because there is no hollow space under the building, infestations of termites and other pests are less common. A slab is less vulnerable to flooding and gas leaks like radon. Concrete foundations, which require fewer steps than piers, are more convenient for the elderly or handicapped.
Don’t forget that pests can still enter a home through the walls. Heating and air conditioning units must be put above ground if there is a slab, and ducts require heavy insulation to maintain the proper temperatures. Tree roots, displaced soil, and freezing temperatures can cause cracking. Avoid cracks by watering your lawn, providing good drainage, maintaining plumbing, and keeping roots away from the concrete. It’s a lot of work, but it’s worth it.
