Should stone impregnating sealers be used in wet environments? Bad idea.
I receive several calls a week with questions regarding impregnating-type sealers for use on outdoor stone, as well as interior wet areas, such as showers, water fountains, etc. The question is simple: Should I seal my stone in these conditions?
The following article explains why stone in wet areas should not be sealed.
About Penetrating Sealers
Penetrating sealers, or impregnators, are designed to penetrate below the surface of the stone and deposit solid particles into the pores of the stone and coat the individual minerals below the surface of the stone. With the pores filled, water, oil, and dirt are restricted from entering the stone. Impregnators can be solvent or water based, and most impregnators are vapor permeable or breathable, which means water vapor is able to pass through the sealed stone.
Why not seal stone in wet environments?
Although most impregnators on the market today our breathable, this does not mean they are suitable for wet environments. Stone sealed with a penetrating sealer is protected from water entering the pores of the stone in liquid form, but these sealers will still allow water vapor in the form of humidity, steam, and other forms to pass into the stone.
Moisture absorption inevitably occurs when stone is exposed to unregulated humidity, temperature fluctuations, and the like. Once vapor enters stone, it can condense and become a liquid. Since impregnators form a protective barrier against water in its liquid phase, this condensation-turned-liquid becomes trapped within the stone’s pores. It will not escape unless it returns to its vapor form and evaporates.
Trapped liquid can result in all kinds of stone problems. Stones with iron content can oxidize, which means the iron can rust and discolor the stone. Natural salts within the stone can dissolve and cause small holes called pitting or flaking of the stone’s outer layer, called spalling. Aesthetically, the constantly saturated stone will appear darker than its natural brightness.
Research continues, but in the meantime…
I strongly believe that careful consideration should be taken before sealing stone in wet environments. With the surge of stone installations in showers and exterior environments in recent years, problems associated with stone sealed with impregnators are becoming increasingly prevalent. Researchers are continuing to experiment and making a strong case that sealing stone in wet environments is inadvisable.
Frederick M Hueston is the founder of Stone Forensics and has over 30 years of experience in the stone business. He has written over 30 books and hundreds of articles. He currently is Chief Technical Direction for SurpHaces and Director of SurpHaces Learning Institute. He hosts a weekly radio show, The Stone and Tile Radio Show and Podcast.