There is a difference between sealing grout joints and sealing tiles themselves, and depending on the type of tile you’re installing you should use one or the other.
Glazed ceramic tiles only need to have the grout sealed. Sealing tile grout gives your tile surface greater water and mildew resistance, and is indispensiable for keep ing grout from getting dirty. Unsealed grout will absorb dirt, grease and grime such that it becomes impossible to clean.
When you should you apply the sealer? For a new tile surface or re-grout, nearly all grout manufacturers advise that you wait at least 48 hours after grouting before aaplying sealers so the grout has time to finish setting. For maintanence of existing tilling, you should re-apply every year or two.
There are two main classifications of sealers: Membrane Forming, and Penetrating.
1) Membrane Forming Sealers: These type sealers will resist water. They are mostly employed as grout colorants with added pigments to change the original color of the grout. Membrane sealers should only be used on unglazed tile because they will not adhere to glazed tiles. They generally stay on the grout’s surface, forming a nonporous membrane with a glossy finish.
In high moisture areas like a shower, water will find it’s way to the tile/grout underlayment- using a membranous sealer makes it hard for the water to get back out and let the grout dry. This can be cause issues associated with prolonged water exposure, like rot, mold and mildew. So best to use this type sealer only with floors.
2) Penetrating Sealers: Penetrating sealers soak into the microscopic voids of the grout. Typically made of silicone or latex solids suspended in a water or mineral spirits base, after application, the base evaporates, leaving the solid material within the grout. The material fills pores and capillaries close to the grout surface and in so doing, reduces the absorption of potentially staining compounds.
Non-pigmented penetrating sealers don’t produce a gloss on the surface, but can slightly darken the grout’s natural color. Use a good quality penetrating sealer like Aquamix for baths or showers. After the sealer dries, the grout looks normal until water is comes into contact with it, and then the water will actually “bead up”, as if it your grout had wax on it.
A silicone, acrylic, or water-based grout sealer is applied to the joints. It’s ok if you get some sealer on the tile surface providing the tile is glazed, but be sure you wipe it off before it dries, or it will be there for good. You need to remove any excess penetrating type sealer from the tile at once. It dries fairly quick, forming a haze on the tile that is about impossible to remove.
For epoxy based grouts, sealing tile grout is not required, unless specifically stated in the manufacturers instructions that applying grout sealer is advised.
For installing porous tile materials such as slate, terra cotta or marble, in order to keep them from staining with use you should seal the actual surface of the tiles. Applying tile sealer will also prevent moisture penetration. Sealing the tile prior to installing, with a top-coat or a pre-sealer, will prevent grout from getting into the tile pores and dulling or hazing the tile surface during grouting.
Use of an acrylic top-coat on the tile surface will prolong your tiles lifespan, but you’ll want to reseal the tile from time to time, about every two years, as it wears off eventually. You’ll know when it’s time when you start to notice your tiles getting harder and harder to keep clean. Do not mix brands and types of sealer; stick to the original sealant for re-application. Try not to use any ammonia-based cleaners on the tiles since it will strip off the sealer.
For entry flooring and other high traffic areas consider an anti-slip coating for your tiles. There are anti-slip coatings now obtainable that are designed to decrease slip and fall incidents by raising the tiles slip coefficient of friction.