What Are Expansion Joints?
Concrete is a rigid material that is always moving. Thermal expansion in Alabama's summer heat, contraction in winter, drying shrinkage as new concrete cures, and soil movement from expansive clay or settling fill all generate stress within concrete flatwork and foundation slabs. When that stress exceeds the tensile strength of the concrete, it cracks, usually in the most inconvenient and unpredictable locations. Expansion joints are deliberate, engineered breaks in the concrete that provide a controlled location for movement to occur, relieving stress before it reaches the cracking threshold. APS Foundation Repair and Waterproofing installs expansion joints in driveways, sidewalks, patios, garage floors, and foundation slabs as both a preventive measure for new construction and a remediation tool for flatwork that has already begun to crack along uncontrolled lines. In Alabama's climate, where temperature swings and expansive Piedmont clay soils are the norm, properly placed expansion joints are one of the most cost-effective investments a property owner can make in the longevity of their concrete surfaces.
How Expansion Joints Work
Expansion joints work by creating a gap or a weakened plane at planned intervals in concrete flatwork. The gap is filled with a flexible, compressible material, typically a closed-cell foam backer and a poured or tooled joint sealant, that allows adjacent concrete sections to move independently without transferring stress across the joint. Joint spacing is based on slab thickness, concrete mix, exposure conditions, and expected thermal range. In existing concrete that has already cracked, saw-cutting and installing expansion joints along or adjacent to existing cracks can convert random fractures into controlled, sealed joints that are easier to maintain and less likely to widen over time. For foundation slabs, expansion joint placement follows structural engineering guidance to ensure that load transfer is maintained across the joint where needed.
“Concrete always wants to crack. Expansion joints do not stop that, they just tell the concrete where to do it. A well-placed joint network turns a cracking problem into a maintenance schedule, which is a much better situation for a property owner than waiting to see where the next random fracture appears.”
How APS Installs Expansion Joints
- 1
Site Evaluation and Joint Layout
APS reviews the concrete surface or slab dimensions, existing crack patterns, concrete thickness, and exposure conditions to determine joint spacing, depth, and type. A joint layout plan is produced for review before work begins.
- 2
Saw Cutting
For new joints in existing concrete, a concrete saw cuts the joint to the specified depth, typically one-third to one-quarter of the slab thickness. Cuts are made straight and to consistent depth for effective stress relief.
- 3
Joint Cleaning and Preparation
Cut joints and existing cracks to be converted to sealed joints are cleaned of dust, debris, and loose material using compressed air and wire brushing. Clean joint faces ensure proper adhesion of sealant materials.
- 4
Backer Rod Installation
Closed-cell foam backer rod is installed in the joint to the specified depth, providing a backing surface for the sealant and controlling the sealant's depth-to-width ratio for optimal flexibility.
- 5
Joint Sealant Application
A flexible polyurethane or silicone joint sealant is applied over the backer rod to fill the joint to the surface level. The sealant is tooled to a concave profile that sheds water and accommodates joint movement.
- 6
Cure and Quality Inspection
Sealant is allowed to cure per manufacturer specifications before traffic or water exposure. APS conducts a final inspection of joint continuity, sealant adhesion, and surface finish before project closeout.
What Expansion Joints Cost and What Is Covered
Cost Range
Project-specific; typically $200 to $800 for residential applications
Warranty
Project-specific; typically $200 to $800 for residential applications
Frequently Asked Questions
My concrete already cracked in the wrong place. Can you still install expansion joints?
Yes. Saw-cutting and sealing existing random cracks is a standard approach that converts uncontrolled cracking into a sealed, maintainable joint. This does not eliminate the existing crack, but it cleans it up, seals it against water infiltration, and reduces the likelihood of further widening.
How often do expansion joint sealants need to be replaced?
Quality polyurethane sealants in a properly designed joint typically last 5 to 10 years before they need inspection and potential resealing, depending on UV exposure, traffic, and the degree of joint movement. APS uses commercial-grade sealants specified for the application.
Do expansion joints affect the structural strength of a foundation slab?
Expansion joints in foundation slabs are placed to relieve stress while maintaining load transfer where structurally required. Dowel bars or other load-transfer devices are specified by a structural engineer in slabs where joint continuity for load bearing is needed. APS follows engineering guidance for foundation slab applications.
What is the difference between an expansion joint and a control joint?
A control joint is a weakened plane, typically a saw cut, that encourages cracking to occur in a straight, planned line rather than randomly. An expansion joint is a full separation between concrete sections with a compressible filler that accommodates larger thermal and movement cycles. Both are important tools; APS will recommend the appropriate type based on the application.
Can expansion joints help with the tile and grout cracking inside my home?
Interior tile and grout cracking along structural joints in the slab below is often a sign that the slab is moving. Proper expansion joints in the slab, carried through the tile and grout layer, are the correct long-term fix. Simply replacing grout without addressing slab movement results in recurring failure.