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How to Fix Foundation Cracks

Foundation cracks can be troublesome to repair, depending on the cause of the problem. The majority of foundation cracks are a result of settling, which can occur when the home sits on less than stable footings. In most instances footings become unstable due to loose fill or soil erosion, and either cause must be corrected before any foundation repairs are made. After the cause has been corrected, we can address the severity and nature of the foundation crack.

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Why Did My Foundation Crack?

Home foundations sit on long strips of concrete in the ground called footings, or footers. Footers must be poured onto undisturbed or compacted soil because concrete requires adequate support or it will crack under its own weight. In some cases a builder may have dug a hole, but neglected to compact the bottom of the hole before pouring the concrete. Because of the enormous weight the concrete will support, over time the footer will sink into the loose dirt, causing it to crack.

A similar problem occurs when erosion is uncontrolled around the foundation. Loose gutters, incorrectly placed downspouts, and poor grading can cause ground and rainwater to erode the sides of the footers. Without adequate side support, the footers can be crushed by the weight of the structure and begin to crumble, often resulting in a foundation crack.

Can I Repair My Cracked Foundation?

Repairing a foundation crack is within the skillset of an average do-it-yourselfer, but success will often depend on the age and severity of the crack. For example, if a 100 year old home experienced a foundation crack, it is very likely the crack occurred long ago and the home has settled around it. In most cases, these cracks are no longer affecting the structure of the home, but they may allow insects and debris to enter the crawlspace.

Other cracks, especially vertical ones, often indicate a foundation problem that must be corrected because it usually indicates a broken footing. Most professionals would not recommend repairing the foundation crack until the cause is found, because unless the cause of the movement is solved, the crack will likely reappear. Once the cause of the crack has been corrected we are usually left with an unsightly foundation crack to repair.

Will I Need Expensive Tools to Repair a Foundation Crack?

In small foundation repairs, most work can be done with simple hand tools a homeowner would likely have. Foundation crack repairs typically involve filling in the crack with masonry crack sealer or cement, and are not considered a structural repair because no additional bearing support is added. Depending on the repair method used, more elaborate tools like hammer drills and jacks may be needed, but most repairs will not. Foundation cracks can occur in either poured or masonry block foundations, but both repairs will often be made the same way, using some form of crack sealer. 

How to Repair a Foundation Crack (Step-by-Step)

Most professionals use mortar to repair foundation cracks because it looks good and is designed to work with masonry. Using mortar is common, but a slurry made from cement or synthetic crack sealers also work well. Most pros use mortar because it looks the best and allows the technician to disguise the repair. Other products like crack sealing caulk do a good job, but they tend to shrink as they cure, making the repair more visible.

Step 1 Prepare the Surface

First, we must remove any debris still attached to the crack. Especially with concrete cracks, the fiberglass strands in the concrete can prevent loose debris from falling out. Any loose debris may prevent the mortar from contacting the foundation, and result in a bad repair. Most pros use a cold chisel (designed for masonry) to remove any debris and slightly widen the crack to accept more mortar.

To ensure a good bond with the foundation, the goal is to increase the surface area of the crack to allow for more contact with the mortar. To do this, we use the cold chisel to gently tap away any material that looks suspect. If in doubt, take away a little extra, but make sure not to create a hole if the foundation is hollow. Once the debris has been removed and the crack widened, it’s time to install a backer.

Step 2 Install the Backer

If the crack is more than ¼” wide, it is recommended to install a cement backer in the crack before applying the cement. The backer will prevent the mortar from falling all the way through the crack if the wall is hollow, such as with a concrete block foundation. Most professionals use open cell expanding spray foam for this purpose, as it sticks to anything and expands to fill the crack. Foam backer rod or crumpled newspaper can also be used, but spray foam is worth the effort.

Some cracks will extend all the way through the foundation and be visible from both sides. In these situations, the spray foam can be installed from both sides of the foundation in the same way, with the same goal. If the foam expands too much and fills in the crack, it can be scraped away with a trowel or utility knife. However, make sure the foam has completely cured before moving to the next step, which is mixing the mortar.

Step 3 Mix the Mortar

Next, the mortar is mixed with water to form a slurry. A five gallon bucket, mixing paddle, and cordless drill make this step much easier, but hand tools like a trowel or small shovel can be used. The goal is a mixture about the consistency of toothpaste, so if the slurry seems too stiff to apply smoothly, a little water can be added. After the correct consistency is achieved, the wall should be moistened with a sponge.

Step 4 Apply the Mortar

Wetting the foundation before applying the mortar is important, because the foundation will draw the water away from the mortar, making it dry too quickly. Adding the extra water prevents this convection, and allows the mortar to cure normally. If desired, an additional latex bonding agent can also be mixed with the mortar to increase its adherence to the foundation. Once the mortar is mixed and allowed to rest for ten minutes or so, it can be applied with a masonry trowel to fill the crack completely.

After the mortar has begun to set, a texture can be applied to help disguise the repair. The wait time required will vary with the conditions, but will generally be about thirty minutes after application. Most professionals use a damp sponge to gently wipe the mortar, blending it into the texture of the foundation until the repair essentially disappears. After the mortar has completely dried it can be primed and painted to match the rest of the foundation.

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