Posted: Fri Dec 13, 2019 1:48pm
With respect, I don’t see any point in sealing them, and it won’t last outside anyway. They would have been very unlikely ever to have been sealed when these kinds of raw/rough terracotta tiles were all that there was for flooring! Just do what my mother used to do with her terrace composed of genuine extremely antiqued terracotta tiles - scrub them intermittently and sweep them daily.
Once the efflorescence has gone - and it may keep reappearing for years - wash them down and leave them to get on with it. Of course, one of the original UK methods of sealing unglazed floors - in this case, quarry tiles, which although much harder are in principle ‘fired earth’! - was to wash them over with milk as this penetrates and forms a very effective sealant.