Sweep or vacuum the flagstones thoroughly. Wash them with warm water and a sponge or mop. Let the stone air-dry completely before proceeding.
Cover nearby flooring and baseboards with masking paper and painter’s tape, if necessary.
Clear small children and pets from the area, and open nearby windows for ventilation. Put on safety gloves and goggles.
Apply the penetrating sealer or stone enhancer with a brush, sprayer or roller -- as directed by the manufacturer. Wipe away any excess with a clean, lint-free cloth. Don’t treat a larger area than you can wipe clean before the excess sealer dries.
Let the sealer dry for the amount of time specified on the product's label. Apply an additional coat, if desired.
Let the treated stone cure for the amount of time specified by the manufacturer. Do not allow anyone to walk on the stone until it’s fully cured.