What to Put Between Flagstone: A Guide to Choosing the Perfect Filler

Understanding the Importance of Fillers for Flagstone

When it comes to creating a beautiful outdoor space, flagstone is a popular choice for pathways, patios, and other hardscape features. Its natural beauty and durability make it a great option for adding charm and functionality to your landscape. However, one important aspect that is often overlooked is the choice of filler material between the flagstone pieces.

Fillers play a crucial role in the overall performance and aesthetics of your flagstone installation. They not only help to stabilize the stones and prevent shifting but also add visual interest and enhance the overall look of the surface. Choosing the right filler material is therefore essential to ensuring a long-lasting and visually pleasing flagstone project.

The Purpose of Fillers

The primary function of fillers is to provide stability to the flagstone surface. They help to prevent the stones from moving, settling unevenly, or becoming loose over time. By filling the gaps between the stones, these materials create a solid and secure base that can withstand foot traffic, weather conditions, and other external factors.

Another important purpose of fillers is to enhance the aesthetic appeal of the flagstone installation. The right filler material can complement the natural beauty of the stones, creating a cohesive and polished look. It can also add texture and contrast, allowing you to customize the appearance of your outdoor space to suit your personal style.

Choosing the Perfect Filler Material

Now that we understand the importance of fillers for flagstone, let’s explore some common options and factors to consider when choosing the perfect filler material:

  1. Crushed Stone: Crushed stone is a popular choice for fillers due to its excellent drainage properties and durability. It comes in various sizes, allowing you to select the right grade for your project. The angular edges of crushed stone interlock, providing stability and preventing stones from shifting.
  2. Gravel: Gravel is another common filler material that offers excellent drainage and stability. It comes in different colors and sizes, allowing you to achieve a unique and decorative look. However, it’s important to choose gravel with rounded edges to prevent it from shifting or becoming uncomfortable underfoot.
  3. Sand: Sand is a versatile filler material that is easy to work with and provides good stability. It can be used for both dry and wet installations, depending on your project requirements. However, it’s essential to choose a sand with the right texture and consistency to prevent it from washing away or becoming compacted over time.
  4. Mortar: Mortar is a more traditional filler option that provides maximum stability and prevents weed growth between the flagstone. It creates a solid and permanent bond between the stones, ensuring a long-lasting and secure installation. However, it should be noted that mortar can be more challenging to work with and may require professional assistance.

When choosing the perfect filler material, it’s important to consider factors such as the type of flagstone, the desired aesthetic, the climate, and the intended use of the surface. Consulting with a professional or seeking advice from a reputable supplier can help you make an informed decision and ensure a successful flagstone project.

In conclusion, fillers are a crucial component of any flagstone installation. They provide stability, enhance the aesthetic appeal, and contribute to the overall performance and longevity of the surface. By understanding the importance of fillers and choosing the right material, you can create a stunning and durable flagstone feature that will be enjoyed for years to come.

Key Facts

  • Choosing the right filler is crucial for maintaining the stability and aesthetic appeal of your flagstone patio or pathway.
  • Fillers help to prevent weed growth, erosion, and shifting of the flagstones.
  • The ideal filler material should be durable, permeable to water, and easy to maintain.
  • There are various options available for fillers, each with its own unique qualities and advantages.

Types of Fillers


  • Sand is a popular and cost-effective filler choice.
  • It provides stability, allows for proper drainage, and prevents weed growth.
  • Choose high-quality, coarse sand to ensure better stability and longevity.


  • Gravel is a versatile filler that offers excellent drainage and stability.
  • It comes in various sizes, allowing you to choose the perfect option for your specific project.
  • Smaller gravel can be easily compacted while larger gravel adds a decorative element.


  • Grit is a fine, crushed stone that works well as a filler between flagstones.
  • It creates a solid surface and is resistant to weed growth.
  • Grit provides a natural and rustic appearance.


  • Mortar is a more permanent filler option that creates a solid, stable surface.
  • It requires professional installation and is ideal for areas with heavy foot traffic.
  • You can choose colored mortar to match or contrast with your flagstone.

Maintenance and Considerations

  • Regular maintenance is important for all types of fillers to prevent weed growth and maintain stability.
  • Remove any debris or plant matter that accumulates between the flagstones.
  • Consider using a polymeric sand or joint stabilizing sealer to enhance the durability and longevity of the filler.
  • Choose a filler that complements the overall design and style of your flagstone patio or pathway.

Factors to Consider When Choosing Flagstone Fillers

When it comes to creating a stunning flagstone pathway or patio, choosing the perfect filler is crucial. The right filler not only enhances the visual appeal of your project but also ensures long-lasting durability. With so many options available, it can be overwhelming to make a decision. To help you out, we have compiled a list of factors to consider when choosing flagstone fillers.

1. Climate and Weather

One of the first factors to consider is the climate and weather conditions of your area. Different fillers have varying levels of resistance to extreme temperatures, moisture, and freeze-thaw cycles. For instance, if you live in an area with harsh winters, it’s important to choose a filler that can withstand freezing temperatures without cracking or shifting.

Expert Tip: Consult with a local landscaping professional or a supplier who can provide guidance on the best fillers for your specific climate.

2. Foot Traffic

The amount of foot traffic your flagstone area will receive is another crucial consideration. Fillers should be selected based on their ability to withstand heavy use and the potential for wear and tear. For high-traffic areas, it’s important to choose a filler that is durable and resistant to erosion. On the other hand, for areas with minimal foot traffic, you can opt for a more delicate filler.

3. Aesthetic Appeal

While functionality is important, the aesthetic appeal of your flagstone project should not be overlooked. The filler you choose should complement and enhance the natural beauty of the flagstone. Consider the color, texture, and shape of the filler in relation to the overall design scheme. You may also want to select a filler that matches the existing landscaping elements or the architectural style of your home.

Expert Tip: Bringing home samples of different fillers and comparing them against your flagstone can help you visualize the final result.

4. Weed and Pest Control

Weeds and pests can quickly ruin the look and integrity of your flagstone project. Choosing a filler that effectively controls weed growth and deters pests is essential for its long-term maintenance. Some fillers come with built-in weed inhibitors or have natural properties that repel pests, reducing the need for constant upkeep.

5. Ease of Installation

If you are planning a DIY project, it’s crucial to consider the ease of installation when choosing flagstone fillers. Some fillers require special tools or techniques, while others can be easily installed by homeowners with basic skills. Opting for a filler that aligns with your level of experience and available time will make the installation process smoother and more enjoyable.

6. Maintenance Requirements

Flagstone fillers have varying maintenance needs, and it’s important to choose one that matches your desired level of upkeep. Some fillers may require regular reapplication or resealing, while others are virtually maintenance-free. Consider the time and effort you are willing to invest in maintaining the filler, as well as the associated costs.

7. Cost and Availability

Lastly, it’s essential to consider the cost and availability of the flagstone fillers. Prices can vary significantly depending on the type, quality, and source of the filler. In some cases, certain fillers may be difficult to source in your area, leading to increased costs or delays in your project. Researching and comparing prices from different suppliers can help you find the best filler that fits your budget and is readily available.

By considering these factors, you can confidently choose the perfect filler for your flagstone project. Remember to consult with experts, explore various options, and prioritize both functionality and aesthetics. With the right filler in place, your flagstone pathway or patio will not only be visually pleasing but also built to withstand the test of time.


When it comes to filling the gaps between flagstone, choosing the right filler is essential. Not only does it add visual appeal to your outdoor space, but it also plays a crucial role in ensuring the stability and durability of your flagstone installation. In this comprehensive review, we will explore some of the most popular fillers for flagstone and discuss their pros and cons. By the end of this guide, you will be equipped with the knowledge to make an informed decision and create a stunning flagstone patio or pathway.


Sand is a classic choice for filling the gaps between flagstone, and for good reason. It is readily available, affordable, and easy to work with. Additionally, sand allows for natural drainage and helps prevent weed growth. However, it’s important to choose the right type of sand for your project. Coarse sand is recommended for larger gaps, while fine sand works best for narrow joints.


If you prefer a more rustic and textured look, gravel can be an excellent filler for your flagstone. It comes in various sizes and colors, allowing you to customize the appearance of your outdoor space. Gravel is also highly permeable, allowing for efficient water drainage. However, it’s worth noting that smaller gravel may shift over time and require occasional refilling or leveling.

Polymeric Sand

Polymeric sand is a modern solution that offers both stability and aesthetics. It is a mixture of sand and polymers that hardens when exposed to moisture, creating a firm bond between the flagstone joints. This prevents weed growth and discourages ants or other insects from burrowing between the stones. Polymeric sand is available in different colors to match your flagstone and provides a long-lasting, low-maintenance option.


If you are looking for a more permanent and solid filler, mortar is the way to go. Mortar creates a strong bond between the flagstone, ensuring stability and preventing shifting or wobbling. It also provides a smooth and finished look. However, it’s important to note that using mortar can be more time-consuming and labor-intensive compared to other fillers. Additionally, mortar may not be suitable for areas with heavy foot traffic or areas prone to freezing and thawing.

Native Soil

If you prefer a natural and organic look, using native soil as a filler can be a great option. Native soil blends seamlessly with the surrounding landscape and creates a harmonious and earthy atmosphere. However, it’s crucial to ensure that the soil is well-compacted and stabilized to prevent erosion and shifting. Regular maintenance, such as adding more soil as needed, might be required to keep the gaps adequately filled.


Choosing the right filler for your flagstone is a decision that should not be taken lightly. Each filler option has its own unique advantages and considerations. Sand offers affordability and ease of use, gravel adds a rustic touch, polymeric sand provides stability and low-maintenance, mortar ensures permanent and solid joints, while native soil blends seamlessly with the natural surroundings. Consider your preferences, budget, and the specific requirements of your project before making a final decision. No matter which filler you choose, proper installation and regular maintenance will ensure a beautiful and long-lasting flagstone surface.

Why Choosing the Right Filler for Your Flagstone Is Crucial

When it comes to flagstone installations, choosing the perfect filler is not only a matter of aesthetics but functionality as well. The right filler can enhance the overall look of your flagstone path or patio while providing stability and durability to ensure it withstands the test of time. To help you make an informed decision, we’ve put together this comprehensive guide on selecting the right filler based on your desired aesthetic and functionality.

Determining Your Desired Aesthetic

Before diving into the world of fillers, it’s essential to have a clear vision of the aesthetic you want to achieve with your flagstone installation. Are you aiming for a natural, rustic look or a more polished and contemporary feel? The choice of filler can greatly impact the final appearance of your project. Take a moment to envision your ideal outcome, and let’s explore the options.

Crushed Gravel

If you’re looking to create a more traditional and organic feel, crushed gravel can be an excellent choice. Available in various sizes and colors, crushed gravel can add a rustic charm to your flagstone installation. Plus, its rough texture provides excellent traction, making it ideal for areas with high foot traffic.


For a sleek and refined look, mortar can be an ideal filler. Mortar creates a smooth and seamless surface between flagstone pieces, giving your installation a modern and polished appearance. It also provides stability and strength, making it suitable for larger areas or projects that require extra durability.

Polymeric Sand

If you’re concerned about weed growth and want a low-maintenance option, polymeric sand might be the answer. This advanced filler contains polymers that, when activated by water, harden and lock the flagstone pieces together. Not only does polymeric sand prevent weeds from sprouting, but it also minimizes erosion and improves the overall stability of your installation.

Considering Functionality

While achieving your desired aesthetic is important, it’s crucial to also consider the functionality of your flagstone installation. Different fillers offer various advantages that can enhance the longevity and usability of your project.


If your flagstone installation is exposed to rain or other sources of moisture, proper drainage is essential to prevent water accumulation and potential damage. When selecting a filler, opt for materials that allow water to flow freely between the flagstone pieces, such as crushed gravel. This will help maintain the structural integrity of your installation and prevent water-related issues.


In some cases, flexibility is key, especially for flagstone installations in areas with shifting soil or heavy freeze-thaw cycles. To ensure your project can withstand these conditions, consider using a flexible filler. Polymeric sand, with its ability to expand and contract, is an excellent choice as it accommodates slight movements without compromising the integrity of the installation.


If you prefer a low-maintenance option, look for fillers that require minimal upkeep. While crushed gravel may need occasional replenishment due to erosion, it generally requires less maintenance compared to mortar or polymeric sand. Mortar, on the other hand, may require resealing over time to maintain its pristine appearance and prevent cracks.

In Conclusion

Choosing the right filler for your flagstone installation is a balance between achieving your desired aesthetic and ensuring functionality. Consider the overall look you want to achieve and the specific functional requirements of your project. Whether you opt for crushed gravel, mortar, or polymeric sand, each filler has its unique benefits that can enhance the durability and beauty of your flagstone installation. By taking the time to select the perfect filler, you can enjoy a stunning and long-lasting result that will truly stand the test of time.

Frequently Asked Questions

1. What is flagstone and why is filler needed?

Flagstone is a type of flat stone used for paving. It is laid in a random pattern, leaving gaps between the stones. Filler is needed to stabilize the flagstone and prevent shifting or weed growth in these gaps.

2. What are the different types of filler options for flagstone?

There are various filler options available for flagstone, including sand, gravel, crushed stone, polymer sand, and mortar. Each option has its own benefits and considerations, such as ease of installation, durability, and aesthetic appeal.

3. How do I choose the right filler for my flagstone?

Choosing the right filler depends on factors such as the intended use of the area, climate, desired appearance, and personal preference. For example, sand is a common and versatile filler, while mortar provides a more solid and permanent solution.

4. Can I use regular sand as filler for flagstone?

Yes, regular sand can be used as filler for flagstone. However, it is important to use sand that is specifically meant for paving purposes, such as polymeric sand or jointing sand. These sands have additives that help them bind together and resist erosion.

5. How do I install filler between flagstone?

The installation process for filler between flagstone varies based on the type of filler being used. Sand can be swept into the gaps and then compacted, while gravel or crushed stone may require additional compaction or leveling. Mortar, on the other hand, is typically mixed and applied between the stones using a trowel.

6. How often should I replace the filler between flagstone?

The longevity of filler between flagstone depends on various factors such as foot traffic, weather conditions, and the type of filler used. Regular maintenance, including sweeping and topping up the filler as needed, can help prolong its lifespan. In general, it is recommended to inspect the filler annually and replace it if necessary.

7. How do I prevent weed growth between flagstone?

To prevent weed growth between flagstone, it is recommended to use fillers that are weed-resistant or inhibit weed growth, such as polymer sand or mortar. Additionally, regular maintenance, such as removing any weeds that do appear and keeping the gaps free of debris, can help prevent weed growth.

8. Can I use multiple types of filler between flagstone?

Yes, you can use multiple types of filler between flagstone. This can be done for aesthetic purposes or to achieve specific functional requirements. For example, you may use sand for most gaps and mortar for areas that require extra stability, such as steps or high-traffic areas.

9. How do I clean and maintain the filler between flagstone?

Cleaning and maintaining the filler between flagstone is relatively simple. Regularly sweeping the area with a broom and using a leaf blower can help remove debris and prevent the buildup of dirt and leaves. If the filler becomes discolored or stained, it can be power washed or scrubbed with a mild detergent.

10. Can I change the filler between flagstone if I’m not satisfied with the appearance or performance?

Yes, you can change the filler between flagstone if you are not satisfied with its appearance or performance. The process will depend on the type of filler being used. For example, sand can be easily replaced by sweeping it out and adding new sand, while mortar may require more labor-intensive removal.