What Do You Lay Under Flagstone: A Comprehensive Guide

When it comes to creating a beautiful flagstone patio, one of the most important steps is to lay a proper foundation. After all, you want your installation to last for years to come. While some may think that simply placing the flagstone on the ground is enough, this can lead to an unstable and uneven surface over time. To ensure a sturdy and level patio, it’s recommended to start with several inches of compacted gravel as a base. This provides a solid foundation and helps with drainage. On top of the gravel, a layer of stone dust, also known as decomposed granite or DG, is typically added.

Can You Put Flagstone Directly on Dirt?

When installing flagstones directly on dirt, it’s crucial to prepare the surface properly. Start by removing any vegetation, rocks, or debris from the area where you plan to lay the flagstones. Next, ensure that the soil is compacted and leveled to create a stable foundation for the stones. This can be done by tamping down the soil with a hand tamper or renting a plate compactor for larger areas.

After the soil is prepared, it’s recommended to lay a landscape fabric or geotextile underneath the flagstones. This will help prevent weed growth and aid in stabilizing the soil. The fabric should be cut to size and placed directly on the compacted soil, ensuring that it covers the entire area where the stones will be laid.

Once the fabric is in place, you can begin laying the flagstones. Start by arranging them in the desired pattern, leaving a small gap between each stone for joint fillers. It’s important to choose stones that are thick enough and have a flat surface to ensure stability. You can use a rubber mallet to gently tap the stones into place and ensure they’re level.

To fill the gaps between the flagstones, there are several options available. One popular choice is polymeric sand, which is a mixture of sand and binding agents that harden when exposed to moisture. This creates a solid yet flexible joint filler that helps prevent weed growth and erosion. Another option is to use a mixture of sand and cement, which can be swept into the joints and then moistened to harden.

How to Choose the Right Type of Flagstone for Your Project

Choosing the right type of flagstone for your project is crucial to ensuring it’s durability and aesthetic appeal. There are several factors you should consider when making your selection.

Firstly, consider the purpose of your project. If you’re looking to create a patio or walkway, you may want to opt for a flagstone with a smooth, flat surface for easy walking. On the other hand, if you’re planning to use flagstone for a retaining wall or natural-looking staircase, you might prefer a more irregular, textured stone for a rustic appearance.

Next, think about the color and overall look you want to achieve. Flagstone comes in a variety of colors, ranging from earthy browns and grays to vibrant blues and reds. Consider the surrounding landscape and the style of your home to ensure that the flagstone you choose complements the overall aesthetic.

The thickness of the flagstone is another important consideration. Thicker stones are typically more durable and suitable for high-traffic areas, while thinner stones can be used for decorative purposes or in lower-traffic areas. Keep in mind that thicker stones may also require more support, such as a concrete base or additional bedding material.

Lastly, consider the type of flagstone that’s readily available in your area. Local suppliers may have different options and variations, so it’s a good idea to visit a stone yard or showroom to see the different types of flagstone in person. This will allow you to assess the quality, texture, and color of the stone before making a decision.

By considering these factors and choosing the right type of flagstone for your project, you can ensure a beautiful, durable, and long-lasting installation that enhances your outdoor space.

When considering the best thickness for flagstone, it’s important to take into account the specific project at hand. Whether it’s a retaining wall, pond, or waterfall, the recommended thickness typically falls within the range of 2 to 4 inches. This is because flagstone is often exposed to various weather conditions and outdoor elements, so a sturdy thickness ensures durability and longevity.

What Is the Best Thickness for Flagstone?

When it comes to flagstone, the thickness of the stone plays a crucial role in determining it’s longevity and stability. The best thickness for flagstone is generally around 2 to 4 inches. This thickness level is recommended because flagstone is often used in outdoor projects, such as retaining walls, ponds, or waterfalls, where it will be exposed to the elements for the majority of it’s decorative life.

Thicker stones are generally more durable and resistant to wear and tear over time. They can better withstand fluctuations in weather conditions, such as freezing and thawing cycles, without cracking or deteriorating.

Another factor to consider is the aesthetics of the finished project. Thicker flagstones have a more substantial look and feel, which can enhance the overall appearance of the space. They create a sense of solidity and permanence that’s often desired in outdoor design.

This thickness level ensures stability, durability, and aesthetic appeal, making it suitable for a wide range of outdoor projects.

When it comes to installing a flagstone patio, ensuring proper drainage is crucial. This can be accomplished by excavating the area to a depth of at least 8 inches. In order to maintain a level surface, it’s recommended to add 6 inches (4 inches compacted base plus 2 inches sand) to the thickness of your flagstones. Planning and preparation are key in creating a long-lasting and visually appealing patio.

How Deep Should Base Be for Flagstone?

When it comes to laying flagstone, one of the most important considerations is the depth of the base. It’s crucial to excavate the area to a depth of at least 8 inches to ensure proper drainage. Additionally, the finished flagstone patio should be level with the surrounding yard, creating a seamless transition between the two areas.

To determine the exact depth to excavate, it’s recommended to add 6 inches to the thickness of your flagstones. This calculation takes into account the layers that will be added to create a sturdy and stable base for the flagstones. The first layer is typically a 4-inch compacted base material, such as crushed stone or gravel. This layer helps to provide a solid foundation and aids in proper drainage. On top of the base layer, a 2-inch layer of sand is added, which allows for leveling and helps to prevent any shifting or movement of the flagstones.

How to Design Different Patterns and Layouts Using Flagstones

  • Creating a checkerboard pattern
  • Designing a random mosaic layout
  • Making a circular flagstone pattern
  • Constructing a herringbone design
  • Crafting a brick bond layout
  • Developing a basket weave pattern
  • Designing a stepping stone pathway
  • Building a flagstone patio
  • Creating a flagstone garden border
  • Designing a flagstone walkway

When it comes to choosing a suitable material for laying flagstones, sand is an option that may seem appealing at first glance. However, it’s crucial to be aware of it’s limitations. One major drawback of using sand is it’s tendency to erode, be it through water, wind, or the activities of ants. Fortunately, there’s an alternative that proves to be more reliable and long-lasting: stone dust, also known as screenings or decomposed granite. In the following sections, we will delve deeper into the benefits and reasons why stone dust prevails as the preferred choice when creating a stable and enduring foundation for flagstone installations.

Should I Use Sand Under Flagstone?

When it comes to laying flagstone, the question of what to lay underneath it’s a crucial one. Many people wonder if sand is a suitable option, but the truth is that sand may not be the best choice. One of the main problems with sand is it’s tendency to wash away when exposed to water. The action of water can erode the sand, causing it to shift and lead to an uneven surface for your flagstones.

This can be especially problematic if you live in an area prone to windy conditions. Another issue with sand is that it can be carried away by ants. These small creatures are known for building tunnels and pathways underground, which can displace the sand beneath your flagstones.

To combat these problems, stone dust, also known as screenings or decomposed granite, is often recommended as a better alternative to sand. Stone dust is made up of finely crushed stone and provides a more stable base for your flagstones. It compacts well, creating a solid foundation that will help prevent shifting and unevenness.

Using stone dust under your flagstones also has the advantage of being resistant to erosion. It’s compact nature means that it’s less likely to be washed away by water or blown away by wind. Additionally, stone dust is less attractive to ants, making it a more durable and long-lasting option for your flagstone project.


In conclusion, when laying flagstone for a long-lasting and durable installation, it’s crucial to establish a solid foundation. This can be achieved by preparing the ground with several inches of compacted gravel, providing stability and drainage. This finely pulverized stone mixture consists of small and varied particles, including gravel and sand, which together offer optimal support for the flagstone. By using these essential materials in the proper order, you can ensure that your flagstone patio or pathway remains sturdy, level, and aesthetically pleasing for years to come.

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