Staining, freeze-thaw damage, efflorescence, salt and acid attack are all related directly to the tendency of a substrate to absorb molecules of liquid. A penetrating sealer works by dramatically reducing this tendency to absorb moisture to protect the tile or stone. This is done by altering the level of surface energy of the substrate thus reducing capillary action. This in turn allows liquids to flow through the sponge-like structure of stone and other porous materials.
How much moisture the substrate absorbs and how much of the staining agent damages the surface generally depends on how much interaction a solid surface has with the staining agent. The more interaction there is, the more likely the solid surface will be susceptible to stains. However, it must also be noted that not all liquids are staining agents and how much surface tension a liquid has also significantly influences the level of staining that occurs.
Characteristically, surfaces that are porous have high levels of surface energy, making them very susceptible to wetting which ultimately increases chances of staining. To reduce exposure to moisture, a surface’s energy must be reduced down to less than that of the staining agent’s surface tension. This is what penetrating sealers achieve.
It is important to note that penetrating sealers do not fill the pores of your substrate. This unique chemistry allows for a breathable surface preventing damaging hydrostatic pressures. Should a contaminant after sealing discolour a surface, maintenance will now be substantially easier as contaminant is prevented from penetrating deep into substrate. Usually removal will be as simple as applying a good quality pH neutral cleaner for most organic spills.
In order for a staining agent to work its way around a penetrating sealer, it must have a surface tension measurement lower than that of the penetrating sealer. You’ll know that surface energy is lower than the surface tension of a staining agent when beading occurs. Beading dramatically lowers the number of points the staining agent can come into contact with. Most of the time negative capillary action is achieved through beading so no staining happens at all. Negative capillary action simply means none of the staining agent is absorbed into the surface, hence no staining.
While a penetrating sealer works to create a strong repellant surface, it does still allow water vapor to travel through the substrate, This is achieved as penetrating sealers do not block or fill up pores but rather simply change the surface energy to prevent staining. The substrate will therefore retain most of its natural porosity which will allow water vapor to move within it as nature dictates. It must be noted that hydrostatic pressure is prevented from building up from within since water vapor can still freely escape the substrate. This kind of “breathable” action is what differentiates it from a waterproof coating.
If you’re trying to decide whether or not to use a penetrating sealer, keep in mind that it doesn’t create a film so it won’t alter the appearance of natural stone and its surface texture. It will, however, reduce or eliminate staining from freeze-thaw damage, efflorescence, salt/acid attack, biological growth like mold and mildew, and improve general dimensional strength and natural protective barriers.