How to Seal a Flagstone Patio

A flagstone patio.
What You'll Need
Yard broom
Power washer
Fine grade sand
Acid-free paving sealant (water or solvent based)
Large Paint Roller and brush/industrial pressure sprayer
Safety goggles (if using sprayer)
Safety mask

A flagstone patio is a great option for those seeking a natural and organic feel to their exterior design. However, with time, the hues of an untreated natural flagstone patio can become dulled by wear and the elements, while an unsealed patio is open to erosion from a number of factors. Sealing a flagstone patio is the best way to protect and preserve this feature.

Step 1 - Clear and Prepare the Flagstone Patio

Using a yard broom sweep the flagstone patio area of any loose debris. Once the patio is cleared of debris, use the power washer to remove any stubborn build-up of dirt or plant matter including moss and lichens. Allow the patio area to dry thoroughly.

Step 2 - Prepare Patio Joints for Sealing

Using a fine grade sand (children’s sandpit sand is a good choice) top up the level of sand at the joins of the flagstone patio. To do this, pour the sand onto the patio surface and sweep backward and forward using a yard broom until the level of sand is equal across all of the joints in the patio. The sand should be just below the level of the stones themselves, since a flush sand join can be drawn onto the roller during application causing an uneven finish. Clear patio of any excess sand and other debris with the yard broom.

Step 3 - Apply Sealant to the Flagstone Patio

Depending on the size of your patio you may wish to apply sealant manually using a paint roller or with the help of an industrial sprayer. With both methods you will need to start at the corner farthest from the entrance to the patio and work backward applying an even layer of sealant to both flagstone slabs and joins. If using a roller, it is a good idea to work your way along the sand, applying sealant with a brush and allowing it to go off before beginning to roll the surface as this will minimize the possibility of messy sand pick-up when you start applying with the roller. If using an industrial sprayer, ensure you are wearing safety goggles and wear a safety mask to protect from fumes if you have opted for a solvent-based sealant. Allow the first coat to dry thoroughly.

Step 4 - Apply Additional Coats of Sealant

All flagstone patios will need at least two coats of sealant and those in areas where they receive high footfall or extreme elemental exposure may benefit from a third coat as well. Apply subsequent coats of sealant in the same way as the first. Note that there is no need to apply sealant to the joints with a brush for subsequent coats as the existing layer of sealant will have tamed any stray sand. Re-seal the flagstone patio every two years.