Best Expansion Joint Sealants for Concrete Construction

An expansion joint provides major stress relief in wall, floor, and facade projects. This component allows building materials to shift a safe amount without taking structural damage.

However, even the “glue” of the team needs support sometimes.

Expansion joints are often an afterthought as a project wraps up. The contractor is trying to close out a job, and may not use the right type or caliber of product (often a sealant instead of a mechanical joint). This is one of several ways an expansion joint can fail.

We’re here to teach you the proper way to use sealant in an expansion joint – and that starts with proper product selection. Let’s decode how you should be approaching sealant selection, then pick apart the pros and cons of each popular option. In the spirit of competition, we’ll also hand out “best concrete expansion joint sealant” awards at the end.

(Related Resource: 8 Types of Expansion Joints to Know)

How Should You Use Sealant in an Expansion Joint?

Joint sealant is a material that has cohesive properties to keep water and debris out of an assembly. It goes on the outside of the joint, providing a tight barrier. Most savvy expansion joint users add a sealant post-installation in any project of consequence.

To be clear, it is not an acceptable filler material for wide gaps. You need an actual mechanical joint product for that. The common maximum gap sizes for using popular sealants are:

• Silicone – 1”
• Polyurethane – 1.5”
• Acrylic latex – 0.5”

These are general guidelines; you should check for specific sealant properties and job site conditions that may impact results.

How to Find the Best Expansion Joint Sealant for Concrete, Etc.

You might also know expansion joints by another name: movement joints. It’s a funny thing. The overall product is really what’s filling the gap between slabs or masonry, while the sealant is most responsible for accommodating movement.

Expansion joint products must allow shifting (to a certain point) and prevent water infiltration and other threats that cause cracks and other structural hazards.

Put these priorities top-of-mind when deciding how to fill expansion joints in your concrete application:

• Flexibility: If the structure’s expected movement will be highly dynamic, its components may require an ultra-low-modulus silicone sealant. These highly elastic sealants can better adapt to thermal cycles, vibration, and other structural movement.
  
  
• Load-bearing capacity: Structures (i.e. bridges) that face exposure to heavy traffic need a more “structural” sealant. Expansion joint sealants for horizontal installations tend to have high tensile strength so they can withstand frequent movement and weight.
  
  
• Chemical durability: Exposure to chemicals and UV light over time can weaken a joint. A chemical-resistant product can extend the structure’s expected life span and reduce maintenance costs.
  
  
• Physical durability: Joints need more wear resistance in areas where traffic is a concern – from vehicles to stiletto heels.
  
  
• Aesthetics: If it’s important for the installation to blend in nicely, you’ll want a sealant that matches or complements the surrounding elements. Some products will match a substrate better than others. The supplier may also offer color matching.
  
  
• Compatibility: Be sure the sealant and joint filler are compatible with each other – and the substrate itself – so you don’t lose adhesibility.
  
  
• Requirements:  Job site conditions and regulations (i.e. fire or seismic risks) also may narrow your path to a decision. In enclosed, occupied areas, using a low-VOC (volatile organic compound) product may be the right thing to do.

We’ll revisit these at our awards ceremony below.

3 of the Best Expansion Joint Sealant Materials

The never-ending debate among contractors is between silicone and polyurethane sealants. Those can capably cover most commercial construction situations, but other options are also worth judging for your use case:

Silicone (The Best?)

Pros: 

• Flexible and resistant to pressure changes
• Naturally resistant to mildew & mold
• Chemically altered to strengthen it, providing greater resistance to temperature & pressure change
• High performance on a wide range of surface materials

Cons: 

• Higher up-front price point
• Poor abrasion resistance

Silicone expansion joint sealant is a combination of organic and inorganic compounds. It consists of silicone polymers, which cure to form a flexible, rubber-like seal.

Only one-part/component silicone sealant is suitable for expansion joints. Also, while silicone sealant adds movement capability to horizontal, vertical, and other joint types, it’s not applicable on some other types

This product has an expected life span of 20 years. In many applications, you won’t beat that with another material.

Polyurethane

Pros: 

• Great against water, chemicals, & oil
• High tensile strength for handling heavy loads
• Great tear and abrasion resistance

Cons: 

• Short service life – may become brittle over time
• Service temperature range is much smaller

(Pro Tip: Extreme temperatures can affect the flexibility and curing process of any sealant.)

Polyurethane expansion joint sealants are versatile, elastomeric adhesives made of inorganic compounds. The polymers cure to form a tough, flexible seal. 

Polyurethane sealants require replacement or maintenance every 5-10 years.

Both one-component and two-component polyurethane products are usable in expansion joint installations. The key differences are:

Acrylic Latex

Pros:

• Lowest cost of the group
• Installation, tooling, & cleanup are simple
• Adheres to a wide variety of surfaces
• Easy to paint over
• Environmentally friendly
• Doesn’t make you gag like a nail salon

Cons:

• Poor resistance to extreme weather conditions (especially UV)
• Lower movement capability (typically 7-10%)
• Not strong enough for heavy-duty use
• Prone to staining and difficult to clean

Acrylic sealant consists of an environmentally friendly formula. It consists of synthetic polymers, water, latex, and fillers that don’t emit much in the way of VOCs.

Unlike most eco-friendly or healthy products, it’s low in cost. It can be a versatile, economical choice for many expansion joints in interior environments. 

Latex expansion joint sealant adheres to concrete, masonry, wood, and other materials. You’ll find it in kitchens and other areas where contractors want a nontoxic product.

However, where you might be most familiar with it is in bathrooms. Walk inside Gillette Stadium, and you’ll see CMUs (concrete masonry units) in every restroom. Builders overlay these blocks with a latex sealant. 

Another typical use of acrylic latex is as a quick fix around window and door frames, but it can survive in light-duty outdoor applications as well.

… That is, to a point. Expect this construction product to last 5 years or less. Its flexibility is middle-of-the-pack, with products ranging from 12.5-25% in movement capability.

Awards for the Best Concrete Expansion Joint Sealant Go To …

In virtually any building facade or horizontal concrete layout, the joints are the weak spots. The right expansion joint sealants can turn that weakness into an advantage for your structure or building envelope.

Speaking of which, the awards for best expansion joint sealant for concrete and other construction projects go to …

🥇 Most Movement Capability: Silicone

🥈 Strongest: Polyurethane

🥉 Most Durable (Chemical): Silicone

🎖️ Most Durable (Physical): Polyurethane

🏅 Aesthetics: Acrylic Latex

🏆 Compatibility: Polyurethane

🪙 Bang for Your Buck: Silicone

Don’t just take our word for it. As you choose a product to seal an expansion joint, pause and check the job site’s surroundings. Consider the material makeup of the surface and the joint, as well as environmental risks like humidity and UV exposure.

If you need more support, check out our manufacturer list: