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If they used a grout colorant and it was applied correctly it should be able to withstand cleaning.  Maybe they used some type of paint that is attracting dirt?  I would not use high pressure cleaning unless it was in a commercial kitchen or an industrial application.

It might be possible to buff scratches out depending on how hard the glaze is, but you might take the risk of causing more scratches.  Good Luck.
 

If in fact you do have glazed ceramic tile (porcelain tile is a type of a ceramic tile) then the staining is likely trapped in the body of the tile behind the glaze.  There is no way to remove the staining if that is the case unless you remove the tile and fix the moisture problem.

If the tile is an unglazed tile then there is a chance you can possibly remove the glaze with a poultice product and process.  Poultice stain removers are normally used on stone products but could work on an unglazed tile.  You will have to go through a trial and error process to determine what type of poultice and process works the best.  Although if the excessive moisture problem isn't repaired and if you are able to remove the stain then it is likely it will return over time.

The best way to clean a tile floor is to use a scrub brush on an extended handle so you don't have to be on your hands and needs.  This method makes sure that textured surfaces and the grout are adequately cleaned.  Purchase a neutral based tile cleaner and add to your water.  Some types require rinsing and others don't.  Then use a wet and dry vacuum to pick up the dirty water.  This is an important step because quite often people leave the dirty water to dry on the tile and grout surface that causes it to turn grey and look dirty over time.  This cleaning method can be done weekly or monthly depending on the use of your tile floor.

Between the full cleaning process you can use a tile spray cleaner to clean up spots as necessary.

If it is only the color of the epoxy grout that is a problem you can apply an epoxy grout colorant over it and change the color and make it more uniform.  Again the grout surface has to be properly prepared. 

The epoxy haze can be removed with epoxy cleaners.  If the tile is a strong unglazed/throughbody tile you can use sand and a detergent and scrub the haze off.

There are companies that specialize in sealing and cleaning floors.  Check with the manufacturer of the cleaning products you select for referrals.

If there is a cement residue then a diluted phosphoric or Sulphamic acid can be used.  Acid will not remove grease or some other organic stains.

I would first use a degreaser or a detergent.  Wash the pavers down well and while wet apply the cleaner and let set for 5 minutes.  Then scrub with a brush on an extended handle.  Then either wash off with clean water into a drain or use a wet and dry vacuum to pick up the dirty water.  Next rinse with clean water again.  Let the pavers dry thoroughly and apply a penetrating sealer if you want a natural look or use an enhancer sealer if you want more of a wet look.  Be sure to wipe the excess sealer off with a lint free cloth after about 5 minutes.

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.

I've never heard of it being used during manufacturing.Some do using it to clean up cement film after installation, but it isn't recommended unless it is a mild acid and greatly diluted i.e. sulphamic acid and some phosphoric acids.

Good Luck!

Although these tiles are very dense and considered impervious in terms of absorption they can still stain.  These tiles do have micro pores where contaminates can be lodged.  If you put metal on any surface and it gets exposed to moisture, as you would expect for an exterior application, then you would expect rust to occur.  The rust may be more difficult to remove on some products than others depending on the composition and treatment of the product.

The etch marks can be removed by re-polishing the surface after the spots have been completely cleaned removing any accompanied stains from the alcohol.  You may need the help of a professional stone refinisher.

These stains can be minimized or avoided by sealing the stone, using glass coasters, and cleaning surfaces with spills and residues right away. Good Luck!

The Marble Institute of America (MIA) states in their design manual that "Organic Stains, such as those caused by coffee, tea, tobacco, paper, food, urine, leaves, bark, and bird droppings may cause a pinkish-brown stain.  For indoor stone stains, clean with 12% hydrogen peroxide and a few drops of ammonia." 

Non-sanded grout is designed for grout joints 1/8" wide or less.  Sanded grout is normally designed for grout joints 1/8" wide or larger.  Grout joints over 1/2" wide need a heavier gauge blend of sand to perform well.  1/8" wide grout joints can use either one, but sanded grout tends to be more stable and doesn't shrink as much.

Soft polished stones or soft glazed tiles can scratch when being grouted with a sanded grout, so always test the sanded grout with the tile first to make sure it doesn't scratch it.

The best way to clean textured floors, or any tile floor and its grout, is to use a tile cleaner manufactured for that purpose or a neutral base cleaner and scrub the floor with a brush (make sure it doesn't scratch the tile) on an extended handle so you don't have to get on your hands and knees.  Then use a wet and dry vacuum to pick up the dirty water.  Rinse if necessary.

Some of these less stable granites are treated with resin at their processing plants to stabilize the stone during its shipping and fabrication.  So these resins enhance the color of the stone and some resins can be removed or smudged with a solvent like alcohol.  You would need to try to get a stone fabricator or renovator to see if they could treat the area and blend it in with the rest of the stone.

Some alcohols can etch the surface of a softer polished surface. Sometimes glasses that had alcohol in them can leave rings on some softer polished surfaces.  Again true granites are normally very resistant to chemicals. 

If it was a cement film then a diluted solution of vinegar or a prepackaged diluted sulphamic or phosphoric based cleaner would likely work.  Do not use any acidic product that is not manufactured for the use with ceramic tile or it could permanently damage the surface of the tile.  Acidic based products can etch the surface of glazed ceramic tiles, and polished stone surfaces.

It might be a latex haze.  There are special products for removing latex based hazes.  If you used an epoxy grout then it could be an epoxy haze and then you have to use a special product for removing epoxy haze.

If the grout is cement based then a diluted vinegar solution with a scrub brush might clean it up, since acid attacks cement.  If there was latex or polymer in the grout then acid may not work work and it may require a latex removal product.  There has to be caution in using anything with acid or using a scrub brush because it could damage the tile finish. Test a small spot first and don't proceed if you are not satisfied. 

In some cases the pigment in the grout can stain a ceramic tile surface or a natural stone surface if it has a degree of porosity; particularly if the grout is a contrasting color from the tile.  In these cases a grout release or sealer can be applied to the surface of the tile before grouting and this will act as a bond breaker to keep the grout from sticking to the tile surface.

Sounds like you have a slate textured finish on your tile.  That type of tile will have tendency to collect dirt if you don't clean it properly. If you mop it and let the dirty water dry on the tile then the resultant dirt residue will find its way into those crevices.  To clean the tile use a neutral base cleaner manufactured for cleaning tile. Get a brush on an extended broom handle and scrub the floor with the tile cleaner.  It is no more effort than mopping.  Then get a wet and dry vacuum and pick up the dirty water, so you don't leave a dirt residue on the tile. 

Sometimes you can just use vinegar diluted with water and it may be enough, but maybe not.  It is best to purchase a pre-diluted acidic cleaner. 

Before apply the acidic cleaner make sure the flag stone is saturated with water so the acid solution will not absorb deeply into the stone.  Use a brush to scrub with the cleaner.  Afterwards make sure you flush the area with clean water until the acid is gone.   Good luck.
 

First try test cleaning a small area with a neutral based cleaner and scrub brush.  Be careful not to scratch the sealer.  If that doesn't do it then you will likely need to strip the sealer and then reapply the sealer. 

Generally speaking some polished and glazed tiles are sensitive to acidic material that can cause etching that will result in a dull finish.  Some sealers will give tile a polished look and when subjected to some types of solvents will tend to cause them to become dull in those spots.

The more porous a tile or grout the more susceptible it is to staining.  The more texture you have on the surface of the tile or grout the more it will tend to pick up dirt and the more difficult it is to clean, but the more slip resistant it will be.

Tile and grout sealers help prevent staining and help make it easier to clean dirty tile and grout.  Although the sealer has to be applied regularly, which will vary depending on how much wear and tear or climatic conditions it is subjected to.  Rule of thumb is if water doesn't bead up (like water on a new car wax job) when sprinkled over their surfaces then it needs to be resealed.  Although make sure the tile and grout is perfectly clean or you will seal in the dirt or stains.

If the gray stains were not there before the flood instance, the stains are in the area where it was subjected to the floor water, and the stains are emanating from the grout joint towards the center of the tile, then they are likely damp stains.  Three days may not be nearly long enough for the tile to dry out considering it has an impervious glazed surface and can only dry through the grout joints.

I have seen this occur with lighter colored glazed ceramic tiles that have a porous clay body.  The water goes through the porous cementitious grout and the porous clay tile body absorbs the moisture.  Then it may take weeks to dry out completely depending on the temperature and humidity of the room and the extent of moisture content in the concrete substrate that I assume it is attached to.  Water that reached the tile through the grout joint likely got absorbed into the concrete substrate, so the drying process requires the concrete slab to dry too so moisture doesn't continue to migrate up to the tile keeping it damp longer.  You can use heat lamps and fans to try to speed up the drying process. 

If the substrate is not a concrete slab, but is over a wood subfloor then there could be other concerns too.

Good Luck.

As long as you use appropriate cleaning products suitable for use over your type of tile, that you use the cleaning product properly, and you maintain the floor regularly and properly, then the tile should not be any more slippery than its inherit nature predicated by physical properties of its manufactured surface.

A glaze is a glass like substance and normally would not be affected by tile cleaner.  Some very acidic substances like muriatic acid might etch the glaze surface but it wouldn't remove it unless it was in contact with it for a great deal of time.

I wonder if the tile has a resin surface which could be affected by chemicals or maybe the porcelain tile was an unglazed tile that was sealed?

The glaze on the tile is applied at about 2000 degrees F so you can't re-glaze it.  If it is a sealer on it then find out what sealer was used and reapply it in that spot to make it shiny again.  Talk to your tile supplier and installer to find out exactly what type of product you do have.  Good Luck!

You said that it was a porcelain tile, but porcelain tile should technically be impervious at 0.5% absorption.  Although, porcelain tile can have microscopic voids that certain materials can get trapped into the pores of the tile and become difficult to remove.  There are special poultices that can be used to remove certain stains.

Best bet is to contact a company that manufacturer's cleaners and sealers to get their recommendations of products.  You will have to do some trial-by-error testing to determine what will work.

If the cement product has latex mixed with it then you need to use a special cleaner like the product sold by Bostik called Hydroment Remove.

First step is to determine what the residue is made of and then find the solvent or cleaner for removing it.  Next make sure that the cleaner won't harm the surface of the tile being cleaned.  Always test the product out first.

Good Luck!

If you don’t want to do the work yourself then find another company who is willing. 

There are special cleaning products for removing deep stains and there are sealers and enhancers that will improve the look of the floor and make it easier to maintain with less maintenance.

Muriatic acid is very dangerous and can end up burning the grout stain into the stone that becomes permanent if you are not careful.  The muriactic acid has to be substantially diluted if it is used.  Sulphamic acid is less corrosive and recommended for this type of cleaning but will take more effort to clean it.  If the haze is light enough you can use cheese cloth to remove the haze or if more difficult then use diluted vinegar with cheese cloth and then buff dry.

Make sure you don’t seal the flagstone before you get it completely clean or you may seal in the grout haze.

When using acid it is important to saturate the surface of the stone or tile with water so the acid doesn't tend to penetrate into the stone.  After you apply the acid and scrub with a nylon type of bristle brush then it is very important that you flush the surface of the stone with enough water to remove any acid residuals.

After cleaning the stone and letting it dry thoroughly then apply a penetrating sealer either an enhancing type to bring out the colors or the standard type that will not change the look of the stone.    Good Luck!

Muriatic acid is very dangerous and can end up burning the grout stain into the stone that becomes permanent if you are not careful.  The muriactic acid has to be substantially diluted if it is used.  Sulphamic acid is less corrosive and recommended for this type of cleaning but will take more effort to clean it.  If the haze is light enough you can use cheese cloth to remove the haze or if more difficult then use diluted vinegar with cheese cloth and then buff dry.

Make sure you don’t seal the flagstone before you get it completely clean or you may seal in the grout haze.

When using acid it is important to saturate the surface of the stone or tile with water so the acid doesn't tend to penetrate into the stone.  After you apply the acid and scrub with a nylon type of bristle brush then it is very important that you flush the surface of the stone with enough water to remove any acid residuals.

After cleaning the stone and letting it dry thoroughly then apply a penetrating sealer either an enhancing type to bring out the colors or the standard type that will not change the look of the stone.    Good Luck!

You might consider trying a paint-remover on a small spot to see if it will cause any damage to the glaze or not.  I have seen it work before for removing paint from a ceramic tile, but again we don’t know how sensitive your glaze will be to the paint remover.

I don't know what type of ceramic tile you have.  If you have an unglazed tile with a sealer on it that makes it shine then the cleaner may have removed it or dulled it to some degree and should be able to be restored.

Most glazed tiles are resistant to many non-corrosive chemicals, but they are sensitive to strong acids.  Some glaze tiles are even sensitive to alcohol or mild acids.  These products can etch the surface of the tile so you will not be able to restore it.