Can You Use Cement Between Flagstone?

When it comes to laying flagstone, one question that often arises is whether cement can be used between the joints. While it might seem like a good idea to use cement for extra durability, this approach can actually have some drawbacks. Let's delve into the intricacies of flagstone installation to understand the best practices and when to use, or not use, cement.

Flagstone, a type of natural stone typically used for patios and walkways, adds a unique charm and durability to outdoor spaces. However, the key to a successful flagstone installation lies not just in the stone itself but also in the materials used to secure and space the stones.

Understanding Flagstone Installation

The most common method for installing flagstone is the dry laid, or random laid, pattern. This involves setting the stones directly on a bed of sand, with no mortar used between the joints. This method allows for a more natural,(random) appearance andallows for some movement, which is particularly important for freeze-thaw climates.

In contrast, some installers might prefer the through-the-bed method, where a mixture of sand and cement is used to set the stones. This method provides a more uniform appearance but can limit the ability of the flagstone to move with the ground.

Cement in Flagstone Joints: Pros and Cons

One of the main pros of using cement in flagstone joints is increased stability. Cement can help prevent weeds from growing in the joints and can add a seal against moisture. However, there are significant downsides to using cement.

One major downside is that cement does not allow for the natural expansion and contraction of the flagstone. Since flagstone is porous and can absorb water, it will naturally expand in wet conditions and contract in dry conditions. When cement is used in the joints, it can restrict this movement. If the flagstone expands and contracts, it can crack the cement, leading to an unsightly and potentially hazardous surface.

Alternatives to Using Cement in Flagstone Joints

If you've decided that cement isn't the best option for your flagstone installation, there are plenty of alternatives. One of the most common is polymeric sand, which is a composite material that mixes sand with additives to create a stable jointing material. Polymeric sand provides excellent stability, prevents weed growth and offers some flexibility to accommodate movement.

Another option is pea gravel or decent-sized chips of the same stone as your flagstone. These can be swept into the joints and provide a solid base for walking on while still allowing for some movement.

The Role of Cement in Flagstone Installation

Although cement should not be used in the joints of a flagstone installation, it does have a role to play in the overall process. If you'relaying your flagstone over a concrete base, then you'll need to use a layer of cement to secure the stones to the base. This is known as a full bed mortar installation.

In this type of installation, a mix of sand and cement is used to create a layer about 1 to 2 inches thick. The flagstone is then bedded into this layer and allowed to set. This method can provide a very solid, secure base for your flagstones, but it does limit the ability of the stones to move with the ground.

The Correct Way to Use Cement in Flagstone Installation

The cement in a full bed mortar installation should be mixed with at least four parts sand to one part cement. This is known as a 4:1 mix and helps to provide a strong, stable base for your flagstone. The mix should be allowed to cure for at least 72 hours before the flagstone is installed.

It's also important to note that the base should be prepared correctly before applying the cement. This involves laying down a layer of plastic to prevent moisture from escaping and digging out any low spots to ensure a level surface.

In the end, understanding the role of cement in flagstone installation allows you to make informed decisions about your project. By using cement correctly, you can create a long-lasting, attractive flagstone surface. But remember, when it comes to the joints, it's often best to leave the cement out, opting for more flexible alternatives like polymeric sand or pea gravel.