All flagstone is subject to water stains, particularly in areas where the water supply is alkaline or contains minerals. ... For this reason, all new flagstone paving should be sealed upon completion. A sealer fills the pores in the stone and repels spills.

Should outdoor flagstone be sealed?

All new flagstone for patios should be sealed to fill in the pores within the stone to repel spills. However, glossy finish sealers will compromise the natural look and feel of the stone. Choose instead a sealer that features a penetrating acrylic with a matte finish so the water will bead up when it hits the material.

Does sealing flagstone keep it from flaking?

To help prevent spalling, outdoor flagstone should be coated with a sealer specifically formulated for natural stone. The sealer inhibits water from getting into and under the surface of the flagstone. If your patio has begun to shed layers, Lesslie says, remove loosely clefted pieces before sealing.