Lately we have been getting a lot of requests to seal exterior stone.  Often its tough to give building management and home owners a simple answer other than, “it’s not a good idea.”

Interior stonework finishing

Natural stone in an indoor application is not subject to the same elements as outside. Stone is polished and finished in a completely different manner. In addition, it is usually installed over a subfloor that is going to stay dry.

What happens when exterior natural stone is sealed?

Exterior stone is often installed over a surface that will be exposed to water. If there is water underneath the stone, and the stone is not sealed, ultimately the water will find a way out allowing the stone to dry. If the surface of the exterior stone is sealed, the water will get trapped and can cause an effect called picture framing.  In addition, a situation called efflorescence can also occur.  This occurs when salts and other minerals present in

various stones are exposed to water. During the evaporation process, these minerals seep out of the stone and appear on the surface as white powder, haze or in some cases, a hard white crust.  Road salt, lawn products for example can cause this issue with exterior installations.

Should I use an Impregnating Hydrophobic Sealer?

Some people recommend using an impregnating hydrophobic sealer.   This is a sealer which repels water and will penetrate deeply enough into the material to keep water and dissolved salts well away from the surface. However, in climates where freezing is a concern, such a sealer may lead to damage from freeze/thaw cycles.

If you are looking to improve the look of exterior stone, we offer excellent exterior stonework cleaning services, call 781-793-0700 for a quote or get an estimate online.