Elastomeric Joint Sealant for Concrete | Types, Costs & How-To

Temperature changes make concrete expand and contract, and unprotected gaps in driveways, sidewalks, and garage floors crack without a flexible seal. You install an elastomeric joint sealant for concrete in those gaps to handle movement and keep water out. This guide covers the types, costs, application steps, and which product fits your project.

What Is an Elastomeric Joint Sealant?

An elastomeric joint sealant is a rubber-like compound formulated to seal expansion and control joints in concrete. It bonds to the sides of a gap while staying flexible enough to stretch and compress as the concrete moves with temperature shifts, traffic loads, or moisture changes. Unlike rigid fillers, elastomeric sealants maintain a watertight seal across joints that see regular movement.

These sealants come in several material types: polyurethane, silicone, epoxy, polysulfide, and hybrid formulations. Each offers different trade-offs in flexibility, chemical resistance, UV stability, and cost. The right choice depends on where and how the joint sits.

ASTM C920 Classes: What Movement Capacity Does Your Project Need?

The movement capacity you need depends on how much your concrete joint expands and contracts. ASTM C920 defines sealant classes from ±12.5% to ±100% — the higher the rating, the more movement the sealant can handle before it tears or loses adhesion.

• Class 100/50 (±100% or ±50%) — Extreme movement joints, typically in bridges or large industrial slabs
• Class 50 (±50%) — High-movement exterior joints, often filled with silicone
• Class 35 (±35%) — Moderate movement, a middle option
• Class 25 (±25%) — Common for standard concrete pavement and driveways
• Class 12-1/2 (±12.5%) — Low-movement interior joints with minimal temperature variation

For most residential driveways and sidewalks, Class 25 or Class 50 sealants are the practical choice. Use ASTM C1193 as your guide for proper joint preparation and installation.

Top Elastomeric Joint Sealant Products Compared

The table below shows the most common elastomeric joint sealant options for concrete, with their movement ratings, lifespan estimates, and cost per linear foot. Prices vary by region and project size.

How to Apply Elastomeric Joint Sealant Correctly

Proper application follows five steps, and skipping any of them is the most common reason sealants fail. Work during dry weather with concrete temperatures between 40°F and 90°F for best results.

1. Clean the joint. Remove loose debris, old sealant, and dust with a vacuum, brush, or mild detergent. Sand lightly to create a rougher surface for adhesion. Let the joint dry completely — any moisture trapped under the sealant causes failure.
2. Install a backer rod. Choose a foam backer rod about 25% wider than the joint gap. Press it in to the correct depth: for most moving joints, fill to 50% of the joint width, with a final depth between 1/4-inch and 1/2-inch. The backer rod prevents three-sided adhesion, which tears the sealant when the concrete moves.
3. Apply primer if required. Some sealants need primer for proper adhesion to the concrete sides. Check the manufacturer’s instructions for your specific product.
4. Inject the sealant. Use a caulking gun to fill the joint evenly from the backer rod up to the surface. Avoid air pockets by keeping steady pressure and moving at a consistent speed.
5. Tool the sealant. Immediately after filling, press the sealant into a slightly concave shape using a spatula or putty knife. This forces intimate contact with the joint sides, consolidates the material, and creates a clean finished look.

When done correctly, the sealant sits slightly concave within the joint with smooth, uniform edges. For self-leveling formulations like Sikaflex 2C SL, pouring rather than gun application may be more efficient. Multi-component products require thorough mixing and have a limited pot life — mix only what you can apply before the material sets. Cure time ranges from 4 to 7 days at 73°F and 50% relative humidity, depending on the product.

If you are comparing products for a specific project, see our recommendations for concrete joint sealant for a side-by-side breakdown of top choices.

Common Application Mistakes

Even a high-quality sealant fails fast when installation goes wrong. The ICRI’s guide on joint sealant best practices highlights the same set of recurring errors:

• Overfilling the joint — Excess sealant bubbles and cracks as it cures. Fill only to the surface level, then tool flat.
• Skipping the backer rod — Without it, the sealant bonds to three sides instead of two, and movement tears the center.
• Applying on a wet or damp surface — Moisture blocks adhesion. The joint must be bone dry unless the product specifically allows damp application.
• Working outside the temperature range — Cold concrete (below 40°F) prevents proper cure; hot concrete (above 90°F) causes the sealant to skin too fast.
• Ignoring the primer requirement — Some products, especially polyurethanes on dense concrete, won’t bond without it. Check the label before you start.
• Skipping the tooling step — Untooled sealant has poor contact with the joint walls and an uneven surface that collects dirt and weakens over time.

Choosing the Best Sealant for Your Concrete Surface

Your application method and location narrow the field quickly. The table below maps common project types to the sealant category that fits best.

For water-reactive sealants like SikaSwell, the movement range works differently — they expand when they contact water rather than stretching, making them ideal for below-grade or submerged applications rather than standard expansion joints.

Final Selection Checklist

Before you buy an elastomeric joint sealant for your project, run through this checklist:

• Measure the joint’s typical movement range — match it to the ASTM class you need.
• Choose the material family (silicone for UV exposure, polyurethane for high traffic, epoxy for interior low-movement) based on your specific conditions.
• Check the cure time — some projects need to bear weight or resist water within 24 hours, others can wait a week.
• Confirm the application temperature range in the product datasheet.
• Verify whether the product needs primer or can bond directly to concrete.
• Account for the backer rod depth — fill to 50% of joint width for standard moving joints.

Get this right, and a quality sealant keeps joints watertight and crack-free for a decade or more.