What are the Common Types of Foundation Cracks?

A structure’s foundation serves as its base, and while this is usually a strong and sturdy material, it can be prone to cracks. These cracks may indicate underlying problems with the foundation and can have a significant impact on the stability of the structure. 

The most common types of foundation cracks are premature drying, horizontal foundation, stair step, plastic shrinkage, hairline, vertical, diagonal, overloading slab, settlement, expansion, heavy, structural, and floor cracks.

Foundation cracks differ from one another, and it’s not uncommon to have gaps and cracks with no visible signs on the surface. Most of these cracks would appear near windows, walls, floors, footings, slabs, etc.

common types of foundation cracks

Most of the cracks are due to settling, premature drying, etc. However, it is not a concern; the primary concern is the type of crack to find the correct repair solution.

This article will talk about the various types of foundation slab cracks that are commonly found in structures, along with the best repair solutions for them.

Premature Drying Cracks

Whenever a concrete slab or the top layer loses moisture faster, it can cause cracks. Crusting cracks results during the process of stamping when the top layer is dried to embed patterns.

Crazing cracks take place when the top layer of the slab loses its moisture naturally. This crack takes the shape of a spider web. These types do not appear appealing, but they are harmless for the slab’s structural strength.

Horizontal Foundation Crack

It may occur and lead to a severe issue. This sort of crack happens due to hydrostatic pressure from the exterior walls and can cause a failure in the foundation.

Most of the foundations are built for handling water and soil pressure. Extra pressure because of flooding or heavy rains can cause severe cracks that require quicker repair.

Stair Step Cracks

Block foundations lie flat to stair-step cracks that take place along mortar joints. These pose a severe danger to the integrity of the basement foundation. The two common causes of stair-step cracks are:

  • Foundation sinking or settling in one area
  • Moisture problems in the exterior of the foundation

Note: You can call for expert inspection and repair solutions whenever needed.

Crack in a cinder block building foundation

Plastic Shrinkage Cracks

When you observe concrete in its plastic state, i.e., when it is full of water before hardening, you will notice cracks on the surface. These are called plastic shrinkage cracks.

Whenever water leaves the slab, it leaves behind large voids in between solid particles, and these empty spaces cause cracks on the surface.

Plastic shrinkage cracks occur anywhere in the wall or slab where they almost locate at the corners pointing into the slab. It may also be discovered in the middle of the concrete slab, such as drains, pipes, manholes, and plumbing fixtures.

They grow narrow with time in width. So, it is vital to remember that plastic shrinkage cracks do not only exist on the surface. It extends throughout the overall slab thickness.

Hairline Cracks

These types of cracks happen in the concrete foundations as concrete cures. Hairline cracks do not lead to problems of foundation stability but can result in leakage issues.

If the damage takes place in a short time after pouring the concrete foundation, concrete may have been mixed quickly or poorly. The hairline crack appears frequently in the center of the walls due to the excellent stability of wall corners.

hairline crack in a wall

Vertical Cracks

In foundation walls, vertical cracks appear less severe and do not cause any structural threat. They are commonly found in the poured foundation that runs straight up and down your wall.

Vertical cracks are the most common type of crack in basements which are caused due to the settling over time of the foundation.

Note – If moisture is absent and you can’t fit a quarter in the crack, there is no immediate risk. You can repair this type of crack with epoxy injection.

Diagonal Cracks

Another common type of crack that you may find is the diagonal crack. It runs along the basement or foundation wall at an angle of 30 to 75 degrees.

The diagonal crack may be the thin hairline crack but is wider at one end than the other. Diagonal cracks are due to differential settling of the foundation.

It is usually caused by uneven tension. They’re often seen on houses built on a hill because of the contraction or expansion of soil.

A clear diagonal black fissure

Overloading Slab Cracks

Concrete is a strong building material, but it has limits. Locating excessive amounts of weight and loads on the top of the concrete slab can lead to cracking.

Whenever you say that a concrete mix has a strength of 2000, 3000, or 5000 PSI, it refers to the pounds of every square inch. After heavy snow or rain, expect massive weight and stress on concrete that can result in the cracking of slabs.

Settlement Cracks

This type of crack may appear when the underlying ground has not been prepared or compacted, or it may also be due to inconsistency of subsoil.

The settlement crack occurs as the random crack where the soil of the subgrade was found uneven after pouring concrete. Settlement cracks are more extensive at the top in comparison to the bottom. It is usually continuous that may appear multiple times on a wall.

Expansion Cracks

Concrete slabs tend to expand outwards when they are subjected to heat. Small spaces between the wall and slab caused due to expansion are called expansion cracks.

It occurs when there is a difference between the temperature inside and outside of your home. These cracks may appear near windows, heating systems, fireplaces, chimneys, or other objects that generate heat in concrete.

Heavy Cracks

Another crack that happens because of temperature is a severe crack. Serious cracks occur because of extreme cold weather that leads to the condensation of the slab.

The slab expands and contracts due to temperature fluctuations, leading to big cracks in the foundation.

To fix heavy cracking, you must fill the gaps between the slab and wall with grouts or sealants. These cracks can also be an indicator of some underlying problem that needs urgent attention.

Structural Cracks

It happens when the home was built with defective materials or a poorly constructed foundation. These cracks are usually wide and may even cause separation between walls and floors.

Structural cracks should not be ignored as they can lead to severe damage, especially if they grow in size. It is important to address them immediately so that you don’t have to worry about bigger issues in the future.

Floor Cracks

Floor cracks are relatively common and are usually caused by the settling of the soil. Small cracks may appear in a concrete floor due to ground movement, but they should not be ignored as they can lead to bigger damage in the future.

They must be repaired and fixed to prevent common problems such as damage, moisture, and insects from seeping.

Common Types of Foundation Cracks: Final Thoughts

Understanding the different types of foundation cracks and their causes is an important step in repairing a home’s foundation.

With the right diagnostics and help from professionals, homeowners can quickly get to the root cause of their home’s cracking issues and get it fixed before it becomes a more serious issue.

Structural, floor, settlement, and expansion cracks are serious issues that must be addressed immediately. Other cracks like overload and heavy cracking can be managed with the help of professional contractors.

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