How do you keep flagstone 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.

Why is my natural stone flaking?

Flaking (also called spalling) in natural stone is generally an indicator of sub-florescence, a condition in which mineral salts are carried into the stone by moisture and accumulate beneath the stone's surface, creating stress within the pores of the stone. ... They may be inherent in the stone itself.