Shopping for the right materials can be intimidating if you’re new to home repair. One minute you’re staring at a hairline crack in your basement wall, and the next thing you know, you’re in a home improvement store surrounded by dozens of products. Even worse, not all cracks or foundation damage can be solved by one type of sealant, and there’s no easy way to figure out which one is best by skimming through product labels. To help you make sense of this situation, we’ve compiled this short guide on the different kinds of products that seal foundation cracks.
What Are the Different Kinds of Foundation Cracks?
Before we get into the right products for the job, you need to know what that job is. Your first step should be identifying the kinds of cracks in your foundation; this will help determine what products you need or if you should skip ahead to calling a professional. Here’s a quick overview of the main kinds of foundation cracks, how serious they are, and their most common causes:
- Vertical cracks: These run up and down your foundation walls and are the least serious type of crack you can encounter. These normally result from your foundation setting after it’s built and don’t always represent long-term damage.
- Diagonal cracks: Also referred to as “shrinkage cracks,” these can result from several sources, such as uneven settlement or the earth shifting downhill. They run diagonally from a corner up to the top portion of the foundation. These cracks can indicate short or long-term problems depending on the nature of their source. We recommend monitoring them closely and calling a professional if they grow or change over several months.
- Horizontal cracks: These are the red flags of foundation cracks and represent a serious risk to your home. Horizontal cracks result from hydrostatic pressure created by the soil surrounding the foundation. As the soil pressure increases, it causes the foundation to bow inward, creating cracks. They tend to run along the entire length of a foundation’s wall and are typically straight. If you encounter one of these cracks, we don’t recommend tackling it yourself. Instead, you should call a professional right away.
- Stair-step cracks: Like diagonal cracks, there can be a few different culprits for these cracks, but the most common cause is a differential settlement – this is when different parts of your home’s foundation settle at different speeds and depths, resulting in uneven displacement. These cracks resemble a zigzag or stair-step pattern in solid block foundations or run along mortar lines in brick foundations.
What Kinds of Sealants Exist for Concrete Foundation Cracks?
If you’ve ever been to a home improvement store, you’ll quickly realize there is no shortage of sealants, epoxies, quick-setting concrete, caulks, and foams in the home repair section. If you’ve never used these products, it can be difficult to know what each one is designed to do, and which are suitable for foundation repair.
Below, we review the products you might see in stores or online and discuss which best suits foundation cracks.
Quick Setting Cement
Quick setting cement, or QSC, is a type of cement that sets and hardens extremely quickly. Due to its ease of use and fast drying nature, QSC is used by many home improvement enthusiasts as a quick fix for everything. QSC is typically used to fill potholes, anchor hooks, fill molds, and repair structures. You can use quick setting cement on:
- Concrete floors
- Outdoor steps
- Concrete slabs
Some brands like Quikrete even offer crack repair quick dry cement, which advertises the ability to repair concrete foundation cracks. We don’t recommend using fast dry cement for anything beyond shallow hairline cracks. Quick setting cement can’t reach far enough into most cracks to offer proper structural repair, instead acting as a temporary patch that will flake off later.
Hydraulic cement is a type of concrete designed to waterproof concrete surfaces. It’s strong, dries quickly, is relatively easy to use, and can be applied to vertical surfaces. This kind of cement is what most homeowners go to when patching cracks in outdoor concrete or sealing pipes. It’s effective for sealing foundation cracks but should not be used alone. Hydraulic cement does a fantastic job sealing the outside of a crack as it provides a strong waterproof seal. However, it has a high viscosity and can’t penetrate deep into the crack where most of the fissure resides. As such, if you use hydraulic cement, we recommend first filling the crack with expanding polyurethane foam, then coating and capping the outside of the crack with the hydraulic cement.
Caulks and Crack Sealers
We’re listing these two entries together because they function similarly and have almost identical applications. Caulks and crack sealants are described as any product designed to seal cracks or crevices. They can be composed of various materials, including liquid cement, polyurethane, or latex, and many are designed to be self-leveling. Caulk is typically waterproof, reacts (expands and contracts) to temperature changes, has a fast drying time, and provides an airtight seal between building materials. Sealants are more resistant to weathering and typically last much longer. Both come in squeeze tubes or cylinders for caulk guns.
While both products are great for sealing sidewalks and concrete walls, most don’t provide the strength needed to repair foundation cracks. The one exception is urethane caulk, a type of expanding, sealing foam. Polyurethane foam is great for almost every kind of foundation or wall crack, as it expands into the deepest section of the fissure and creates an airtight seal. Most crack repair kits have special injection ports to get the foam through the entire crack.
To learn more about the differences between caulks and sealers, check out this helpful video from Home Depot:
A resurfacer is a type of concrete mix that combines portland cement, sand, and special bonding polymers to create a smoother, more durable, and stronger holding concrete. Unlike most other concrete, resurfacers are designed to be applied in a thin layer, often over a wide area. This type of concrete is special because it’s extremely strong, often possessing greater pounds per square inch (PSI) than the concrete it’s applied over. While resurfacers are effective for concrete crack repair on driveways and floors, they’re not designed for foundation cracks.
Epoxy is a type of sealant designed to coat the outside of concrete and provide a waterproof seal. Epoxies are different from other sealants in that they’re composed of two chemicals (a resinous material and a hardening agent) that, when mixed, create a much more powerful seal. While more difficult to apply than other entries on this list, epoxy seals will work great on foundation cracks. We recommend foundation repair kits that contain special epoxy injection tools. These kits allow you to better get the sealant deep into the crack, providing a powerful, long-lasting seal.
These compounds are premixed pastes designed as concrete patches for small cracks and holes. These products are the most convenient and easy to use on this list, only requiring a hand trowel and putty knife to apply. However, they don’t possess the strength needed for anything beyond patching small, surface-level damage. Furthermore, these compounds are too thick to get into the deep parts of foundation cracks.
What Kinds of Sealants Are Best for Foundation Crack Repair?
Out of all the types of sealing products mentioned in this article, two stand out as the most effective, polyurethane expanding foams and epoxy sealants. Expanding foam allows you to inject the caulk into the deepest part of the crack, then apply your preferred coating of choice to the outside. Expanding foam is also one of the cheapest and easiest products to apply. The only downside is that expanding foam doesn’t have the strongest hold, so it may fail if your home’s foundation continues to shift.
On the other end of the spectrum, we have epoxy sealants, specifically foundation repair kits that use an injectable two-part epoxy. These kits are designed for serious cracks and damaged foundations. The seal from epoxy provides the highest structural integrity, and the kits come with tools that allow you to fill the entire crack. Unfortunately, they’re some of the most expensive on this list, often costing well over $150, with some high-end kits reaching over $400.
When Is the Right Time To Call a Professional?
Sometimes cracks are foundation problems that go beyond DIY projects, instead requiring the aid of a foundation repair specialist or structural engineer. However, determining when to DIY a foundation problem versus calling a professional can be difficult. Generally speaking, you can DIY a solution if the problem is:
- A hairline crack
- A vertical crack
- Not expanding
- Smaller than a quarter of an inch
However, you should seek the help of a foundation repair specialist if the crack is:
- Larger than one half an inch
- Growing or changing directions after several months
- A horizontal crack
- A diagonal crack
- Accompanied by bulging or warping walls
While wading into the world of foundation repair can be overwhelming, the information provided in this guide should be able to give you an idea of where to start. We also want to mention that you should always install gas detectors inside houses, especially in basements with large foundation cracks. While uncommon, foundation cracks can let in lethal natural gasses.