Control joints and expansion joints in a concrete sidewalk

The short answer

The lines across a concrete walkway are not decoration. They are joints, and they are there because concrete shrinks and moves. NRMCA, the ready mixed concrete industry association, calls joints "simply pre-planned cracks," and says cracks cannot be prevented entirely but can be controlled and minimized by properly designed joints.

A walkway has two main kinds. Control joints, also called contraction joints, give the concrete a weak line to crack along. Expansion or isolation joints separate the walk from things that move differently, such as a driveway, a wall or a light pole. Heaving most often happens at joints, so knowing which kind you are looking at helps you describe the problem and ask the right question.

What a control joint does

NRMCA says contraction joints create weakened planes in the concrete and control where cracks from dimensional changes will occur. The American Concrete Institute (ACI) defines a control joint the same way: a formed, sawed or tooled groove that creates a weakened plane to regulate where cracking happens. On a walkway, these are the grooves that divide it into panels.

The Federal Highway Administration's (FHWA) 2013 sidewalk maintenance guide explains why they are there. Any length of concrete will eventually crack, so methods are used to control it. NRMCA adds that joints relieve the tensile stresses in the slab, are easy to maintain, and are less objectionable than uncontrolled or irregular cracks.

The guidance on how to build them is specific, and it is guidance, not code:

• Spacing. NRMCA recommends a maximum spacing of 24 to 36 times the slab's thickness. For a 4-inch slab, that is about 10 feet, and it recommends no more than 15 feet. FHWA generally recommends a maximum of 24 to 30 times the thickness.
• Panel shape. NRMCA says panels should be square or nearly so, no longer than 1.5 times their width, and not L-shaped.
• Depth. NRMCA says the groove should be at least a quarter of the slab's thickness, and not less than 1 inch. FHWA says a quarter to a third of the sidewalk's depth, and no more than 5 millimeters wide.
• Timing. NRMCA says conventional saw-cut joints should be run within 4 to 12 hours after the concrete is finished, and that if sawing is delayed too long, uncontrolled cracking may occur.
• Wide walks. FHWA says a walk 8 feet wide or wider should also have a control joint along its center line.

FHWA also recommends saw-cut control joints over troweled ones because they leave a smoother surface, and says joints should be level and as narrow as possible. It says decorative scoring should be kept to a minimum, to avoid jarring bumps for people using wheelchairs.

What an expansion or isolation joint does

NRMCA says isolation or expansion joints separate a slab from other parts of the structure. Its examples include walls, footings and columns, and driveways and patios from sidewalks, stairs and light poles. They permit independent vertical and horizontal movement and help minimize cracking where that movement would otherwise be restrained. ACI defines an expansion joint between slabs on the ground as a separation filled with a compressible filler material, and an isolation joint as a separation that allows movement in three directions.

Where they go:

• NRMCA's rules for proper jointing call for isolation joints between slabs and columns, walls and footings, and where driveways meet walks, curbs or other obstructions.
• FHWA says full-depth expansion joints should be placed next to rigid structures such as poles, walls, hydrants and buildings, and isolation joints at the beginning and end of curved sections and at all intersections.
• NRMCA recommends a premolded joint filler, such as compressible foam strips, for isolation joints against building walls or footings.

There is a third kind. NRMCA describes construction joints as the surfaces where two successive pours meet, typically at the end of a day's work. You may see one where a newer panel meets an older run.

What a failed or missing joint looks like

Joints do their work only partly. FHWA says expansion joints are used to control cracking, but that this is only partially effective, because of the forces at work in the soil below. Here is what to look for at and between the joints. Describing what you see is the goal.

A step at the joint. FHWA says that because sidewalks are built with joints to control cracking, heaving most often occurs at those locations, and that displacement often occurs at the joints. ACI calls this faulting: displacement of a slab along a joint or crack. A step is a trip-hazard question first. See sidewalk cracks for how the change-in-level figures are written, and the walkway inspection checklist for how to measure it.

A crack that ignores the joints. NRMCA says the majority of concrete cracks come from improper design and construction practices, and the first it lists is the omission of isolation and contraction joints and improper jointing practices. Its joint sheet also warns that saw cutting delayed too long can lead to uncontrolled cracking. FHWA says longitudinal cracks can run along the middle third of a walk through several joints. Note where the crack runs relative to the joint lines, and how long and wide the panels are.

Cracks near a driveway, wall or pole. These are the places the sources say need an isolation joint. FHWA also links cracks across a walk to uneven subgrade compaction, especially where driveways cross sidewalks. Note whether there is a separation with filler at that edge, or whether the concrete runs straight into the driveway or structure.

Broken edges along a joint. ACI calls a spall next to a joint a joint spall. Note how much of the edge has broken away.

What sealing a joint can and cannot do

ACI defines the two materials in a sealed joint. Joint filler is compressible material that keeps debris out and supports the sealant. Joint sealant is compressible material that keeps out water and solid material. FHWA lists joint sealing among its best examples of preventive maintenance for sidewalks, and the definition it quotes says preventive maintenance is typically applied to pavement in good condition with significant remaining service life.

Sealing is not a repair for a joint that has already moved. Writing about cracks, FHWA says sealants will not hold two sidewalk segments together; they only keep water out of the void. A raised or sunken panel at a joint needs grinding, lifting or replacement, and the method comparison sorts which fits. The sources opened for this page give no sealant product or resealing interval for walkways, so ask the contractor what they would use and why.

When it is the city's question or a professional's

Building or replacing a walkway. NRMCA's first jointing rule is to plan the exact location of every joint, and the timing of the saw cuts, before construction. Ask whoever will pour for the joint plan: where the control joints go, how deep and how soon they are cut, and where the isolation joints meet the driveway, walls and other fixed objects. Sidewalk replacement covers the rest of a replacement job, and the curing guide covers the days after the pour.

A sidewalk along a public street. Ask the city which standards apply; general guidance may not be what governs. For sidewalks the Texas Department of Transportation (TxDOT) builds, its 2024 Item 531 says, "Install joints as shown on the plans." For conventionally formed concrete it says, "Provide pre-molded or board expansion joints of the thickness shown on the plans for sidewalk section lengths greater than 8 ft. but less than 40 ft., unless otherwise directed." That governs TxDOT contracts, not a city's own sidewalks or a private walkway. In Dallas, the City's 2021 Addendum to the regional construction standard (retrieved November 6, 2026) says, in its opening notes, that the City's Department of Public Works will use the latest edition of its Standard Construction Details, File 251D-1, and the North Central Texas Standard Drawings, and adds: "The 251D-1 Standards will take precedence over the Public Works Construction Standards – North Central Texas, standard details." Those details were not opened for this page, so it states no Dallas joint dimension. Check with the city that the address is in before anyone cuts or pours in the right-of-way, and see the Dallas guide for who must repair a Dallas sidewalk.

A step at a joint. FHWA says more communities are using grinding and cutting to make more permanent repairs to displacements at joints. See sidewalk grinding for what grinding involves, and the method comparison for when it fits.

Next steps

Walk the property with the inspection checklist and note each joint with a step, a crack beside it, broken edges, or missing filler. The glossary defines the terms a bid will use. Then use the inquiry preparation guide to gather what a contractor needs, and ask about your project when you are ready.