How to Fill Gaps in Flagstone Patio?

Flagstone patios exude a rustic charm and timeless elegance that can transform any outdoor space into a captivating retreat. However, over time, these beautiful pathways can develop gaps due to natural settling, weathering, and erosion. Filling these gaps not only enhances the patio’s aesthetics but also prolongs its lifespan. In this article, we’ll provide you with a comprehensive step-by-step guide on how to effectively fill gaps in your flagstone patio, ensuring its enduring beauty.

Understanding Flagstone Patios

Flagstone, a type of flat sedimentary rock, is a popular choice for creating picturesque patios. Available in various shades and textures, flagstone adds a unique character to outdoor areas. The gaps that form between these stones are inevitable due to factors like soil movement, temperature changes, and the passage of time.

Tools and Materials

Before embarking on the gap-filling process, gather the necessary tools and materials. A rubber mallet, chisel, broom, and hose are essential for preparing the patio. Depending on your preference and patio type, choose between two common gap-filling materials: polymeric sand and mortar mix. Ensure your selection aligns with the specific needs of your patio.

Preparing for Gap Filling

Begin by thoroughly inspecting your flagstone patio. Identify gaps, loose stones, and any damage that requires attention. Clear the gaps of debris and any loose material. This ensures a clean surface for proper gap filling. Clean the flagstones as well, as the presence of dirt or dust can hinder adhesion.

Filling Gaps with Polymeric Sand

Polymeric sand is an excellent choice for filling gaps between flagstones. Its unique composition allows it to set like concrete when exposed to moisture, providing stability and durability.

Start by evenly sprinkling polymeric sand over the patio’s surface.

Use a broom to sweep the sand into the gaps, ensuring it reaches the bottom.

Gently tap the sand down with a rubber mallet to compact it.

Activate the sand by gently spraying water over the entire patio, allowing the sand to harden.

Once the sand is fully cured, apply a sealant to enhance its longevity and prevent water penetration.

Filling Gaps with Mortar Mix

Mortar mix is an option if you’re dealing with larger gaps or want a more permanent solution. It provides structural integrity to the gaps, holding the stones in place.

Mix the mortar according to the manufacturer’s instructions.

Carefully apply the mortar into the gaps using a trowel, pressing it down firmly.

Smooth out the surface of the mortar to match the level of the flagstones.

Clean off any excess mortar from the surface of the stones before it dries.

Allow the mortar to dry and cure for the recommended time, usually around 24 hours.

Finishing Touches

After the gap-filling process, it’s important to sand down any excess material that might have accumulated on the surface. This ensures a smooth and even appearance. To seamlessly blend the repaired areas with the rest of the patio, consider lightly tapping the repaired stones with a rubber mallet to level them with the surrounding ones. Finally, apply a sealant over the entire patio to protect it from weathering, erosion, and staining.

Preventing Future Gap Formation

Regular maintenance is key to preventing gaps from reappearing in your flagstone patio. Sweep and clean the patio regularly to remove debris that can accumulate in the gaps. Additionally, ensure proper drainage to prevent water from pooling, as excess moisture can lead to gaps and erosion.

Hiring Professionals vs. DIY

When it comes to gap filling, you have the choice between hiring a professional landscaper or tackling the project yourself. Hiring a professional can save time and ensure precision, especially for larger or more complex patios. However, if you’re up for the challenge, DIY gap filling can be a rewarding project that allows you to connect with your outdoor space.


Your flagstone patio is more than just an outdoor space; it’s an extension of your home’s character and your personal style. By following this step-by-step guide, you can fill gaps in your flagstone patio with confidence, restoring its beauty and strength. Whether you choose polymeric sand for flexibility or mortar mix for durability, the result will be a patio that’s ready to withstand the test of time. Embrace the satisfaction of a job well done, and relish in the beauty of your well-maintained flagstone patio for years to come.

Leave a Comment

Your email address will not be published. Required fields are marked *