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Sealing the grout helps keep moisture out, helps prevent staining of the grout, and helps make it easier to clean the grout.  Trapping moisture in the cementitious grout isn't normally a problem because cement gets harder over time when subjected to moisture.

There are a variety of sealers on the market that are recommended for granite tile countertop application.  I would assume they are safe, but the only way to be sure is to look at the specific products Material Safety Data Sheet (MSDS) where they must disclose any information about their product which could be harmful.

There are many types of sealers.  Some are topical sealers and some are penetrating sealers. Some are breathable and some are not.  Some are water based and others are solvent based.  Normally Saltillo tiles are sealed with special sealers for highly porous tiles.   Some sealers are meant to give a natural look, some are meant to give a glossy look, and some give a enhanced look with a slight shine. 

The only way to know how the sealer will react with your particular Saltillo tile is to experiment. Buy a small container of the sealers and test it out to see what you prefer.  Always be sure to wipe any excess sealer off the face of the tile with a lint free cloth right after it is applied or you can get streaking or it will leave a tacky finish.  Follow the sealer manufacturer's instructions for preparation and application. Be sure not to have too high of moisture in the tile substrate or it can lead to a discoloring or efflorescence in the tile.  Good Luck.
 

 I assume you have a glazed ceramic tile, so you want to use a penetrating sealer suitable for that use.  Make sure you wipe dry with a lint free cloth within 5 minutes after applying.

You should go to the manufacturer of the sealer and ask them what to do, because they may have experience on what has caused the condition and how to remediate it.

I have to assume that you have an unglazed tile.  Sometimes if non-breathable sealers are applied over damp material or if the substrate below the tile has a lot of moisture it can cause a cloudy white appearance on the tile.  If that is the case then you do have to strip the sealer off to allow it to dry if the moisture problem is temporary.

If the whitish look in the sealer is due to a contaminate on the surface or moisture on the surface, you can experiment by taking more of the same sealer and applying it over the tile and let it sit for few minutes and then rub to loosen up the sealer on the surface.  Then immediately get a dry lint free cloth and buff the tile surface dry.  See of that will take the white appear away.   Good Luck.
 

First, you must make sure your grout is porous and that it will accept a stain.  If there isn't a sealer over the grout and it readily absorbs water when you put a drop on it, then you just need to first clean it very well and let it dry.  If there is a sealer on it and it won't readily absorb then you have to strip the sealer off or roughen up the grout surface and clean it until it does readily absorb.

Assuming it is an unglazed tile that has previously been sealed; you have to strip the sealer from the tile by using one of the products from a sealer company (see resource section on this website for names of sealing manufacturers).  Once the tile is very porous then you can use a tile or concrete stain, which some of the sealer companies also have.  The stain might also be a sealer or you may have to seal it with another product after you stain it.  Be sure to test it out on a sample first to make sure it is acceptable to you.

Good Luck!

The surface sealers are non-breathable and if moisture gets trapped in the tile under the sealer it could cause a cloudy discoloring. Some of the surface sealers tend to show wear patterns. The penetrating sealers allow moisture in a vapor stage to pass through. They do have some color enhancing versions that will give you somewhat of a glossy look.

The sealers you are referencing are normally used to seal other types of products, and they would have to be qualified to see if they are suitable or not for a ceramic tile application. Make sure they are recommended for food preparation areas.

There are sealers called “Enhancers,” which will seal the tile and grout, but gives it somewhat of a wet look.  They are more commonly used on natural stone to enhance and bring out the colors.  They should be a breathable sealer to allow the tile or stone to breath.  Be sure to wipe all excess sealer off the tile with a lint-free cloth right after you apply it or it could become a sticky surface that will be problematic.

If your tile is very absorbing (over 3%) then the sealer manufacturer may first recommend using a penetrating sealer before the enhancing sealer.

You will have to review the sealer manufacturer’s data sheet on how it is effected by heat and if they have any limitations, but it is common to use these sealers on fireplaces.

It is not required to use an enhancer or not.  It is more a matter of preference.  Normally travertine is sealed with sealers that leave it with a natural look.  If you use an enhancer then you will have more maintenance as you may develop foot traffic patters.

Glazed Ceramic Tile doesn't normally get dull unless the surface is excessively worn, and then I would not expect it to be uniformly dull.  So I'm not sure if you have a glazed or unglazed tile on your counter.  An unglazed tile might be sealed and it may have dulled over time and use.  If it is an unglazed tile then you could apply a sealer enhancer over it to make it more shiny. 

Generally speaking I have found the following method could resolve your problem: Use more of the same sealer over the sticky sealer application by letting it sit for 5 minutes, then rub it in with a lint free cloth, and then buff it dry with a clean and dry lint free cloth.

It could be a glazed tile, which means it has a glass-like substance on the surface that is applied and then fired at a high temperature in a kiln.  In this case all you can do is clean it.  If the glaze surface chips or wears there isn’t any substantial way to repair it.

I’m assuming the whitish finish is a stain and not efflorescence (salts) that have migrated to the surface of the tile.  If it is efflorescence then you need to clean and reseal it.

If the tile has been stained white and a glossy top coated sealer applied it could be an epoxy based sealer that wears well, but is difficult to repair.  You would have to contact a company who specializes in this type of epoxy coatings to have it repaired or contact the manufacturer of the tile who provided it that way.

Unglazed (through-body) Porcelain tile is considered impervious and does not absorb much, although these enhancers might work to some degree.  The enhancers tend to work better on more porous material. 

By the way, if your porcelain tile is a glazed porcelain tile (meaning it has a glass-like substance on the surface called a glaze) then the enhancer will not work because the glaze does not have enough porosity.