Does Flagstone Patio Need to Be Sealed?

Foundation Type

• The foundation layer of your patio can dictate whether you need to seal the stone. For example, a concrete-based structure, or one that is built entirely out of flagstone, really does not need to be sealed because the stone breathes naturally, and will shed moisture naturally. However, if there is wood beneath the structure, the subsequent runoff and seepage can eventually damage the wood, in which case penetrating sealers can be beneficial.

Mortar or Sand Joints

• Mortar or sand joints can also dictate whether you need to seal your flagstone patio. Sand --- much like natural stone --- can breathe normally, which means moisture evaporation occurs naturally. Grout mortars, on the other hand, contain polymers to counteract movement and seasonal shrinkage or expansion, and they can benefit from sealer to protect both the color and the polymers within the grout. While not completely necessary, sealing grouted patios can extend the life of the patio.

Furnished or Unfurnished

• Furniture can scratch the surface of the stone if it is dragged around and proper precautions are not taken. Certain sealers, such as surface sealers, can help protect the surface of the stone, although they should be used only if there is adequate breathing room for the stone from underneath If you have installed your flagstone over a waterproof base, you cannot seal the face of the stone or the moisture will be trapped in the stone, thus discoloring it over time. Only use surface sealers if your stone does not have a moisture barrier underneath the installation. Regular installations, such as with a concrete or wood base that lack a moisture barrier or waterproof layer, can be sealed.

Outdoor Kitchens

• Cooking areas are ideal for using penetrating or impregnating sealers; they help protect the flagstone from grease drippings and other types of messes that are a byproduct of cooking. The same goes for eating areas and washing stations. Seal areas that have food and/or food residue and other potential hazards that can stain or damage the color of the stone.