Concreate, Inc. delivers concrete polishing and custom staining for both commercial and residential projects primarily in Virginia and Maryland (but also up and down the East Coast). We work hand in hand with with designers, architects, project managers, general contractors, tradesmen, and home owners alike from start to finish. We welcome the opportunity to serve your polished concrete needs in every way possible.

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How to Fill Joints in Concrete: 5 Ways to Do It Right

How to Fill Joints in Concrete: 5 Ways to Do It Right

Joints in a concrete floor.

Follow these tips for filling joints in concrete. You’ll get professional-looking results every time!

Key Takeaways:

  • Concrete joints are sometimes necessary to prevent damage
  • You can fill these joints to make the floor look better and prevent debris from building up
  • Filling these joints with grout or a specialized filler is common
  • The process is relatively easy for a trained professional

During installation, planned cuts, called expansion joints, are made in concrete to accommodate movement caused by temperature changes and moisture. Without these control joints, cracks can form randomly on the concrete’s surface. 

Random cracking can affect your polished concrete’s aesthetic appeal, cause the floor to become a tripping hazard, and lead to the concrete’s deterioration and, eventually, its replacement.

While you don’t have to fill expansion joints in concrete, doing so can extend the life of your floor and provide a more polished look. Dust and debris can collect in unsealed joints, making maintenance a hassle. Water can also seep into the joints, leading to chemical reactions that cause the concrete to spall or flake.

Luckily, there are multiple ways you can fill joints in concrete to minimize damage and protect your investment. The best way to fill expansion joints in concrete depends on the extent of the damage, the joint’s width, your budget, and your aesthetic preferences.

The 5 best ways to fill joints in concrete

Filling joints in concrete is essential for the longevity and appearance of your floor. It will also save you time and money in the long run by preventing cracks, trip hazards, and other damage. Here are 5 of the best ways to fill joints in concrete:

1. Grout

Grout is one of the easiest and most cost-effective ways to fill joints in concrete. It is a Portland cement-based product mixed with water and sand and is available in various colors to match your concrete floor. You can also add a stain to grout to create a crisp, unique look. The rigidity and strength of grout make it ideal for filling expansion joints in concrete.

To apply grout:

  1. Clean the joint with a wire brush to remove any dirt or debris.
  2. Mix the grout powder with water, following the manufacturer’s instructions. You can also buy pre-mixed grout at your local home improvement store.
  3. Pour the grout into the joint, using a trowel to spread it evenly.
  4. Tool the grout with a flat-edge trowel to smooth it out and remove any air pockets.
  5. Wipe excess grout with a damp sponge.
  6. Let the grout cure for 24 hours before walking on it or adding weight to it.

2. Flexible polyurea-style joint filler

Flexible polyurea-style joint fillers are a newer option for filling joints in concrete. They are two-part resins mixed and then injected into the joint using a caulk gun to create a flexible, long-lasting seal. 

Polyurea fillers are fast curing, taking under one hour to set. Their superior color stability means they won’t turn yellow or fade over time and can be applied in hot or cold weather. Polyurea joint fillers are also durable and designed to withstand heavy foot traffic and vehicular traffic. 

The application process is similar to grout, but you’ll need a caulk gun to apply the filler. Ensure the filler is flush with the concrete surface to create a smooth transition and avoid trip hazards.

3. Epoxy-based joint filler

Epoxy joint fillers’ high adhesion ability, abrasion, and chemical resistance make them ideal for filling expansion joints in concrete floors with high human traffic and heavy loads, such as in parking garages and warehouses. 

Epoxy fillers are also flexible, which allows them to accommodate slight concrete movement without cracking. Unfortunately, epoxy fillers are more difficult to apply and require a lengthy curing time of up to 72 hours. They also require installation temperatures above 32 degrees Fahrenheit, as freezing temperatures can interfere with curing.

To apply epoxy joint filler:

  1. Prep the joint by cleaning it with a wire brush or vacuum to remove any dirt, debris, or loose concrete.
  2. Mix the epoxy resin and hardener according to the manufacturer’s instructions.
  3. Pour the epoxy mixture into the joint using a manual bulk gun or pump.
  4. Use a trowel to tool the epoxy and remove any air pockets.
  5. Allow 48–72 hours for the epoxy to cure before walking on or adding weight to it.

4. Silicone-based joint sealant

Sealants are a good option for filling joints in concrete that experiences little movement, such as in sidewalks, patios, and driveways. Silicone-based sealants are the most commonly used type of sealant for concrete joints. 

They are long-lasting and form a protective barrier against weather, water, and chemicals. Silicone sealants are also flexible, which allows them to accommodate shrinkage and expansion of the concrete. This prevents the unsightly cracks that can form if the sealant cannot move with the concrete.

Applying silicone sealant is a relatively easy process with a few key steps to follow. You will need standard caulking equipment, such as a caulk gun, silicone sealant, and a putty knife.

To apply silicone sealant:

  1. Remove old sealant or debris from the joint with a putty knife or wire brush.
  2. Cut the tip of the silicone sealant tube at a 45-degree angle to create an opening that is 1/4 inch wide.
  3. Insert the tube of sealant into the caulk gun.
  4. Position the caulk gun over the joint and apply pressure to the trigger to dispense the sealant.
  5. Use a putty knife held at a 45-degree angle to smooth out the sealant.
  6. Wipe excess sealant with a damp sponge. Leave the sealant for 24 hours to cure.

5. Polyurethane-based joint sealant

Polyurethane-based sealants are similar to silicone-based sealants but have higher mechanical and adhesion strength. They are also more resistant to moisture, making them a good choice for expansion joints in concrete subject to frequent temperature and humidity changes, such as in kitchens and bathrooms. 

Since polyurethane sealants are organic, as opposed to inorganic silicone sealants, they have poor UV resistance and will degrade over time when exposed to direct sunlight.

The application process is no different than for silicone sealants. You will need a caulk gun, sealant, and a putty knife. Apply a fair amount of sealant to the joint, using a putty knife to smooth it out. 

Tool the sealant at a concave angle to create a slight trough in the center of the joint. This will help the sealant better adhere to the concrete and prevent it from being pushed out of the joint by traffic or weather.

It’s important to have a thorough understanding of your project’s needs when choosing a joint filler to ensure it’s the best option for your situation.

Extend your concrete’s lifespan with professional joint-filling services

Joints are a critical part of any concrete structure but can also be a weak spot if not properly filled. Over time, joint sealants can degrade, allowing water and debris to enter the joint and cause damage.

The concrete pros at Concreate can inspect your joints and recommend the best way to fill them based on the joint damage, the amount of traffic it experiences, and its environment. We use only the highest quality materials, so you can rest assured that your concrete will be protected for years to come. Get in touch with our skilled team today to learn more about our concrete filling, repair, and restoration services.