How-To Guide
Expansion (isolation) and control (contraction) joints guide where concrete cracks and allow anticipated movement. If joints are unsealed or the sealant has failed, water and salts can enter the joint and accelerate freeze–thaw deterioration, undermining, and spalling; sealing is a preservation measure that helps keep joint areas dry and extend service life.[3][5]
Match material selection and installation to industry standards: ASTM C920 classifies elastomeric joint sealants by type, grade, and movement capability and is the standard used to choose a sealant suitable for the joint’s expected movement and durability needs.[1] Use ASTM C1193 as the installation guide for substrate prep, primer use, backer materials, and joint geometry; follow the sealant manufacturer’s technical data sheet and installation instructions for system‑specific requirements.[2]
For pavement and long‑life exterior joint details, FHWA technical advisories and briefs discuss reservoir dimensions, backer rod use, causes of joint failure, and preservation practices useful for homeowner and public‑works applications alike.[3][4]
Backer rod controls sealant depth, prevents three‑sided adhesion, and creates the recommended concave bead profile. Closed‑cell polyethylene backer rod is recommended for many exterior concrete joint applications unless the chosen sealant manufacturer specifies otherwise; avoid gas‑producing (non‑closed‑cell) materials when the data sheet disallows them.[9][7]
Choose a backer rod diameter that compresses to fit the joint—many product guides and manufacturers recommend selecting a size that yields roughly 25% compression when installed for typical systems; the manufacturer’s instructions will state the acceptable compression range for that product and sealant system.[9][7]
Polyurethane sealants are commonly used for exterior concrete‑to‑concrete working joints because of their adhesion and movement capability. Other chemistries—polysulfide, silicone, and hot‑pour rubberized asphalt—have tradeoffs and typical use cases (for example, hot‑pour materials are commonly used in many DOT pavement joints). Select a chemistry based on movement needs, UV exposure, traffic/abrasion, and chemical exposure for the site.[8][10][3]
Many sealant manufacturers require a primer on concrete to achieve durable adhesion. Do not omit primer unless the product technical data sheet or the manufacturer explicitly states it is not needed for that substrate.[2][8][7]
Industry guidance commonly recommends a sealant width:depth ratio of about 2:1 for working joints (sealant depth roughly half the joint width). Minimum sealant depths for narrow joints and other exact reservoir dimensions may be published by the sealant manufacturer or in ACI/ASTM guides, so check those sources for the chosen product.[2][6][7]
Worked example (units shown): for a joint that is 1" wide, a typical target sealant depth is 1/2" (giving a 2:1 width:depth ratio). If you install backer rod to set the depth, ensure the finished sealant depth is near that 1/2" per the manufacturer’s minimum/maximum depth limits.[2][7]
Remove failed sealant carefully with mechanical tools and use appropriate PPE (gloves and eye protection). Take care not to damage the joint edges—edge damage undermines future adhesion. Consult the sealant and primer SDS for PPE and ventilation requirements when working with solvents, primers, or sealant materials.[2][8][7]
Clean the joint of dust, loose particles, and salts before installing backer rod and sealant; many FHWA and DOT briefs emphasize cleanliness to reduce causes of joint failure such as trapped debris and intrusion of water and salts.[3][4]
Sealing joints is a preservation measure that helps keep joints dry, but it is not a substitute for proper concrete mixture and placement. Primary measures to resist freeze–thaw distress remain proper air entrainment, a low water‑to‑cement ratio, and good curing; sealing reduces water access at critical joint planes and complements these core practices.[3][6][5]
Costs vary with scope. A simple reseal (clean, backer rod, primer if required, and a single bead of sealant) can be low per linear foot in DIY material cost—sealant tubes commonly retail in the $5–$20 range—while basic professional residential caulking estimates from trade sources are often roughly $5–$10 per linear foot for simple jobs. Full joint replacement, edge repair, or heavy remediation increases costs substantially; consult local contractors for firm quotes because prep scope and labor drive price.[14][12][13]
Use appropriate PPE and follow SDS directions for primers and sealants. For joints in driveways, sidewalks, or near traffic, follow DOT and industry guidance for traffic control and public safety while work is underway.[2][3]
Hire a contractor when joints have significant edge spalling, undermined concrete, or when the job requires removal of adjacent concrete to restore joint geometry—these conditions often need more than a reseal and can require concrete repair techniques beyond sealant replacement. Also consult a professional if you are uncertain about primer compatibility, expected movement ranges, or manufacturer system requirements.[7][8]
Do you need to reseal your exterior concrete joints?
Quick checkQuick homeowner checklist for sealing exterior concrete joints.
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