The longevity and usefulness of stone can be extended by sealing its surface effectively, so as to exclude harmful liquids and gases. Modern stone sealers are divided into 3 broad types below and comes in a few different finishes such as enhancer, gloss, semi gloss, matte or clear, depends on it's type:
Topical sealers
Generally made from polyurethanes, acrylics, or natural wax. These sealers may be effective at stopping stains but, being exposed on the surface of the material, they tend to wear out relatively quickly, especially on high-traffic areas of flooring. This type of sealer will significantly change the look and slip resistance of the surface, especially when it is wet. These sealers are not breathable i.e. do not allow the escape of water vapour and other gases, and are not effective against salt attack, such as efflorescence and spalling.
Penetrating sealers
The most penetrating sealers use siliconates, fluoro-polymers and siloxanes, which repel liquids. These sealers penetrate the surface of the stone enough to anchor the material to the surface. They are generally longer lasting than topical sealers and often do not substantially alter the look of the stone, but still can change the slip characteristics of the surface and do wear relatively quickly. Penetrating sealers often require the use of special cleaners which both clean and top up the repellent ingredient left on the stone surface. These sealers are often breathable to a certain degree, but do not penetrate deeply enough (generally less than 1mm) to be effective against salt attack, such as efflorescence and spalling.
Impregnating sealers
Uses silanes or modified silanes. These are a type of penetrating sealer, which penetrate deeply into the material, impregnating it with molecules which bond to the capillary pores and repels water and / or oils from within the material. Some modified silane sealers impregnate deeply enough to protect against salt attack, such as efflorescence, spalling, picture framing and freeze-thaw spalling. Some silane stone sealers based on nanotechnology claim to be resistant to UV light and higher pH levels found in new masonry and pointing. A good depth of penetration is also essential for protection from weathering and traffic.