How to Fill Gaps in Flagstone Patio

If you’re looking to create a stunning outdoor space with a timeless aesthetic, then installing a flagstone patio is a great choice. Not only are they beautiful and durable, but they can also withstand the elements without requiring much maintenance. 

How to Fill Gaps in Flagstone Patio

However, if your flagstone patio has some gaps in it over time due to erosion or settling of soil underneath the stones, then these need to be filled so that the overall appearance is not affected. In this blog post, we will be explaining how to fill gaps in flagstone patio for an attractive and secure finish.

What Is the Best Material to Put between Flagstone?

The best material to put between flagstones is sand or masonry joint compound. Sand is the most common and economical choice for filling in gaps between flagstones, as it can be found at most hardware stores. It’s important to use fine-grain sand so that it will settle properly into the crevices between stones.

Masonry joint compound is a more expensive option but offers extra protection against water seeping through the gaps. This material can be found at masonry supply stores, and its application is similar to that of sand.

With either material, it’s important to make sure the gaps are filled in thoroughly to prevent any future cracking or displacement of the flagstones.

For added protection, many people opt to use a sealant over the sand or masonry joint compound once it’s been applied. This will further protect against water seepage and also provide a smoother and more attractive appearance to the patio.

It’s important to make sure that the sealant is compatible with the material in between the flagstones, so be sure to check with a masonry specialist or read product instructions before application.

When it comes to filling in gaps between flagstones, sand and masonry joint compounds are both great options. With either material, careful attention should be given to ensure that all gaps are filled properly to prevent future damage. For extra protection, a sealant can be applied to further protect against the elements and create an attractive finish.

With these tips in mind, filling in gaps between flagstones can be done quickly and easily!

All Gaps Are Filled Properly

10 Methods on How to Fill Gaps in Flagstone Patio

1.  Choose the Right Materials

The first step in filling gaps in a flagstone patio is to choose the right materials. There are a variety of fillers that can be used, including sand, gravel, and mortar mix. The type of filler you use will depend on the size of the gaps and the look you want to achieve. If the gaps are large, mortar mix may be the best option. If they’re small, sand or gravel could work as well.

2.  Clean the Area

Before you begin filling the gaps, it is important to clean the area. Use a broom to sweep away any debris. Remove any weeds or grass that may be growing in the crevices. Then use a pressure washer to remove any dirt or grime from the surface.

If you don’t have access to a pressure washer, a garden hose with a strong spray setting will do the trick. Although it won’t be as effective, it will get the job done. Once you have cleaned the surface, let it dry completely before moving on to the next step.

3.  Fill the Gaps with Sand

One of the easiest ways to fill gaps in a flagstone patio is with sand. Start by sweeping the patio with a broom to ensure that all dirt and debris are removed from between the flagstones. Then, spread even amounts of sand over the entire surface, filling in any gaps as you go.

Once all the gaps are filled, use a leaf blower or shop vacuum to get rid of any excess sand on the flagstone and around the edges of your patio.

Finally, use a mop or brush to tamp down the sand in each gap and make sure that it’s tightly packed. This will help to prevent any shifting or settling over time. You may need to repeat this process a few times before all the gaps are completely filled.

Any Excess Sand on the Flagstone

The benefits of filling flagstone patio gaps with sand are that it is relatively inexpensive, easy to do, and provides an aesthetically pleasing result.

4.  Fill the Gaps with Gravel

Another option for filling gaps in a flagstone patio is gravel. To use gravel, you will need to fill the gaps with a layer of gravel and then use sand to fill in any remaining spaces. The advantage to using gravel is that it is relatively easy to install, as well as is resistant to weathering, so it will last for a long time.

If you choose this option, be sure to select gravel that is the same color as your flagstones so that it blends in with the overall look of the patio. Also, make sure that you level out the gravel before adding sand, as this will ensure a smooth and even surface.

Once the gaps are filled with gravel and sand, it is advisable to use a sealant to protect the material from water damage and to help lock in the stones.

5.  Fill the Gaps with Mortar Mix

If you want a more permanent solution for filling gaps in a flagstone patio, you can use mortar mix. First, wet the area with a garden hose or power washer. Then, use a trowel to fill the cracks with mortar mix, using as much or as little as needed. 

Once all of the cracks have been filled, use a damp cloth to smooth out the surface. Allow the mortar mix to dry for 24 hours before walking on it or adding furniture back onto it. This will create a more permanent solution for filling the gaps in your flagstone patio.

6.  Add Polymeric Sand

Once you have chosen your filler material and filled all of the gaps, you may want to add polymeric sand. Polymeric sand is a type of sand that contains binders that help it harden when wet. 

This will help to keep your filler material in place and prevent it from washing away during rainstorms or being blown away by windy weather conditions. To apply the sand, spread it over the entire surface of your flagstone patio and then use a broom to work it into the gaps.

Polymeric Sand is a Type of Sand

Once you have done this, spray the Stone patio with a hose to activate the binders and allow them to harden.

7.  Apply Sealant

Once you have filled the gaps with your chosen material and added polymeric sand, you may want to apply a sealant. There are several types of sealants that can be used on flagstone patios, including concrete sealers, acrylic sealers, and epoxy-based sealers. Be sure to read the label carefully when choosing a sealant so that you choose one that is compatible with your filler material.

However, it is important to note that sealants are not always necessary.

8.  Clean Up Any Spills

When filling in gaps between flagstones, it is important to clean up any spills as soon as possible. This will help prevent staining and discoloration of the flagstones due to spilled filler material or sealant. 

Use a damp cloth to wipe away any spills, and allow the flagstones to dry completely before applying sealant or filler material. Once finished, step back and admire the beautiful, completed job! With this easy guide for filling gaps in flagstone patios, you can have a beautiful outdoor space that you and your family can enjoy for years to come.

9.  Remove Excess Filler and Sealant

Once you have finished filling the gaps and applying a sealant, it is important to remove any excess filler material or sealant. This will help create an even surface and prevent cracking or displacement of the flagstones. Use a wet towel or sponge to wipe away any excess material and then allow the sealant and filler to dry, usually for 24 hours.

Use a Wet Down Flagstone Patio

10.  Allow Time for Curing

Finally, it is important to allow the sealant and filler material enough time to dry and cure completely. This will help ensure that it is properly set and secure, preventing water seepage in the future. Depending on the climate and humidity, it can take anywhere from a few days to a full week for the sealant to fully cure.

With these tips in mind, filling gaps between flagstones can be done quickly and easily. The key is to choose the right materials, clean the area, and apply a sealant for extra protection. With a little bit of effort, you can have a beautiful flagstone patio that will last for years to come!


Now that you know how to fill gaps in flagstone patio, While using polymeric sand to fill spaces between stones is the best way to keep weeds at bay, there are other things you can do as well. 

Hand-pulling weed is an option for those who don’t want to use chemicals, while landscaping fabric and organic mulches can also help prevent weed growth. No matter what method you choose, be sure to check regularly for gaps so that your patio stays looking its best.

You Can Check It Out to Seal a Stamped Concrete Patio

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