The Importance of Expansion Joints in Concrete Driveways -

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KEY FACTS ABOUT EXPANSION JOINTS IN CONCRETE DRIVEWAYS

Needed where the new driveway butts an existing slab or foundation.

AKA Isolation Joints (but not the same as Control Joints).
Placed before concrete pour, spaced 12′ or 24′ apart.
Typically ⅜” wide.

Should be sealed with a flexible sealant.
Best to seal the entire concrete driveway with a topical sealer.

Are Expansion Joints in Concrete Driveways Needed?

Expansion Joints in concrete driveways are required wherever the new slab butts an existing slab or foundation such as the garage floor, house foundation or the curb.

Expansion joints give the concrete driveway space to expand and contract when the temperature changes, preventing the development of stress. The expansion joint is also known as an isolation joint as it physically separates the two slabs.

Expansion Joints (aka Isolation Joints) are needed in concrete driveways where the driveway butts an existing slab or foundation such as the garage floor, house foundation or the curb.

When should you use expansion joints in concrete? Almost all the time. Expansion joints are usually required in most slab-on-grade installations, be they interior floors such as a garage or basement floor or exterior slabs such as driveways.

The Importance of Expansion Joints in Concrete Driveways

The only time expansion joints are not required is when you pour an independent concrete slab, such as that to place a shed or above ground pool on.

An expansion joint is especially important for a concrete driveway as:

Driveways are exposed and are hence subject to higher temperature variations

Driveways are typically long slabs and hence the expansion is higher

Where Do You Need Expansion Joints in a Concrete Driveway?

Short Driveways

For short driveways that just connect the garage directly to the curb, expansion joints are only required at the edges where the driveway meets the garage floor and the curb.

Such driveways are usually around 24’ long, just long enough to park cars or pick up trucks. However, the driveway does require contraction a.k.a. control joints. These should be formed or cut such that they are 8’ – 12’ apart.

Long Driveways

Driveways that are longer than 24’ and circular or horseshoe driveways will need more expansion joints. They, of course, need expansion joints at the edges where the driveway meets the garage floor and the curb.

They also require expansion joints at edges where the driveway meets the house foundation or any other rigid obstruction such as a column, pillar, manhole, etc.

Long concrete driveways should be poured in sections and expansion joints should be placed between them. It is easier to pour the concrete and also gives each section room to expand when temperatures rise.

A typical concrete mix truck delivers a load of 10 – 12 yards. This quantity is right for pouring a 6” thick, 24’ X 24’ concrete slab. So for concrete driveways longer than 24’, you can install expansion joints after every 24’.

Each 24’ long section can then be poured from a single concrete mix truck.

How Wide Should Concrete Expansion Joints Be?

Expansion joints in outdoor concrete slabs are recommended to be ⅜ “ wide.

Concrete expands when temperatures rise and contracts when temperatures drop. The thermal coefficient of expansion of concrete is small but significant enough to require expansion joints in concrete slabs.

An unrestrained 100’ long concrete slab could expand by as much as ½ “ – ⅔ “ should the temperature rise from 0° F to 100° F.

An expansion joint that is ⅜ ” wide, will be able to more than handle any expansion or contraction in a concrete driveway, especially if the expansion joints are placed 12’ or 24’ apart.

Expansion Joints Vs Control Joints: What’s the Difference?

The terms expansion joints and control joints are often used interchangeably, sometimes even by professionals. They may look similar but a closer inspection will reveal that they are different. They are designed for performing different functions.

Expansion joints in concrete driveways are placed to separate two sections of the slab independent of each other. Contraction joints are placed within a section of the slab to control where cracks form.

Infographic: Expansion Joints vs Control Joints

Here is a table which highlights the key differences between an expansion joint and a control joint.

Feature	Expansion Joint (aka Isolation Joint)	Control Joint (aka Control Joint)
Placement	Before concrete pour	After concrete pour
Depth	Same as concrete slab thickness	Quarter of concrete slab thickness
Width	Typically ⅜”	Typically ⅛”
Purpose	Separates two slabs to allow for expansion due to temperature rise	Creates a weakened plane to encourage concrete shrinkage cracks to occur within the joint

Should Expansion Joints in Concrete Driveways be Sealed?

Expansion joints should be sealed with a flexible sealant. This will prevent water and other fluids from seeping in and causing damage to the concrete slab. The sealant should be flexible enough to allow the joint to move without cracking.

There are a few different types of sealants that can be used for expansion joints. Some common choices include:

Polyurethane sealant: This is a flexible sealant that is resistant to water, chemicals, and UV rays. Arguably your best option.

Epoxy sealant: This is a strong sealant that is also resistant to water and chemicals.
Bituminous sealant: This is a less expensive sealant that is still effective at preventing water from seeping in.

After using a PU sealant to fill up the expansion joint, you must also seal the entire concrete driveway with a good quality topical sealer.

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The Best Sealers for Your Concrete Driveway or Patio

A topical sealer is essential for protecting concrete surfaces from water permeation that can damage the concrete from within and compromise its lifespan.

I highly recommend Foundation Armor Concrete Sealers. Pick the one that best meets your aesthetic and application preference.