Yes, you can (but there are many cheaper ways of doing it , such as regular tile glue)
Polyurethane scratches easily which will definitely show through your slate tile, also due to the porous nature of all natural stones the poly will become a permanent fixture in your otherwise beautiful tile. So, in that case, it could be done using the latest specifications and design criterion for the sealing of a slate.
Polyurethane is resistant to most glues. Having said that, there are many differently formulated polyurethanes and many new tile adhesives appearing every week. -I would run a test on a small piece of each particular one that you have to see the results.
A coat of shellac can be placed over polyurethane. You should use de-waxed shellac if you plan on placing more polyurethane on in the future.
Tile is a building material you can use in commercial and residential use. There are certain kinds of tile you can use and they can be installed indoors and outdoors. You can choose between ceramic tile, porcelain tile, glass tile, slate, natural stone tile, and other types.
Yes you can, however, ensure that this is the best option before executing. I do this to reinforce the self-stick vinyl tile and laminate flooring in my basement and it works great. I got tired of dropping a knife or something creating a huge gash requiring replacement. The polyurethane layer has protected my floors for years. Occasional reapplication of polyurethane in spots where needed making it look new brand new again versus cutting out and re-sticking a piece of the laminate floor that will never look as good as new...I use the former. There are a lot of nay-sayers out there about polyurethane on vinyl tiles and laminate floors, but I've always had great success.
Yes, you can use polyurethane on painted glass. It is recommended to use the spray rather than dip though because it will be easier. +++ Test on a small, discreet area first to ensure the polyurethane's solvent won't attack the paint.
no. . .that would be a bad idea ceramic tile should not need any kind of coating. . .if you don't like the look, you bought the wrong tile
yes
It is not the best option . Always use polyurethane on polyurethane , acrylic on acrylic and etc ; Is even important to use them of the same brand .
Polyurethane will give a long lasting easy to apply finish. Use a water based polyurethane ans clean up will be much easier. You should get years of wear from a good polyurethane finish.
Polyurethane is an extra-tough material found in paints which also has excellent electrical insulating properties.