I like using LTP. Their sealant worked very well on my travertine floor and grout. They have a liquid that you can brush on/Coat with a cloth or an aerosol propelled version think its called wall and Floor Grout Protector.
I am trying to tile an external corner. I've tacked up a plumb edging strip. This exposed the fact that the perpendicular wall tapers out about 10mm in the bottom 3rd of the wall. (The facing adjacent wall is plumb)
I could botch it and angle the edging strip and taper the tiles but the...