What Is an Expansion Joint?

As you discuss a new cement project with contractors, you keep hearing the phrase "expansion joints." Too intimidated to admit you have no clue what an expansion joint is, you nod, sheepishly smile and read this article to get up to speed before someone asks you another question.

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Why Are Concrete Expansion Joints Necessary?

Expansion joints allow for movement in or between structures, from buildings to concrete pavement. Concrete — like most building materials used in construction — is durable and rigid. That’s great for a foundation or driveway, but not so great when flexibility is needed due to external forces, such as:

• Seismic activity: Homes and buildings in areas with seismic action must adapt to an unstable foundation. Concrete expansion joints can help a building flex as needed.

• Thermal expansion: The expansion and contraction of materials based on temperature is called thermal movement. Expansion joints help concrete withstand temperature fluctuations.

• Settling: Soil changes over time due to pressure. As your cement foundation settles, expansion joints help your home adjust to the uneven surface.

What Happens When Cement Expansion Joints Fail?

When concrete can no longer adapt to expected movements, it eventually gives way to stressors. Cracks can appear in pavement and foundations. In time, the structure may become unstable and eventually collapse. Water infiltration increases the progress of this deterioration.

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Where Are Concrete Expansion Joints Used?

In residential construction, you often find them in foundations, driveways and where patios or sidewalks adjoin other surfaces.

The quantity and types of expansion joints depend on the following factors:

• Building or pavement size

• Regional characteristics, such as temperature, soil structure and seismic activity

• Attributes of the material and adjacent components

Residential homeowners should follow local and state building code guidelines regarding using expansion joints in building projects.

Expansion joints are commonly used to ensure a flexible interface between pool coping and the adjacent material, whether tile, brick or concrete. These joints allow for the expected movements around the pool bed and are critical to the longevity and appearance of your pool.

Expansion joints are one of several movement joints in concrete construction. You’ll often find them placed where the concrete meets another surface, such as a decorative wall or column. Cement expansion joints are formed with job-specific materials and put into place before the workers pour concrete.

To help prevent cracks in concrete, contractors use a control or contraction joint. A narrow slit is cut or grooved into the concrete after it's been poured but before the final set. Establishing a crack in the concrete ahead of time prevents random cracks from developing due to temperature changes and frost heaves.

As your driveway ages, it’s normal for concrete expansion joints to widen and the original support material to decay or fall out. You can reseal these joints as a DIY job or call a home repair service. Control joints are usually narrower and don’t proceed all the way through the concrete. You can easily clean out any dirt residue to prevent buildup and water damage. If your control joint is excessively wide, you may caulk it as well.