Thanks for the reply. This is the stuff I've recently used:
http://www.dta-aus.com.au/products/AS1L - I'm fairly sure the active
ingredient is Sulfonic Acid.
I've used it on some modern ceramic tiles in the bathroom and shower,
and also on some (very) old outdoor ceramic or cement tiles with some
sort of glaze or polish on them. It has worked incredibly well on the
bathroom tiles - even better than I thought it would. But it has only
had a tiny non-slip effect on the old, glazed, outdoor tiles. Do you
know of any other products (or active ingredients) that work well on
cement or ceramic tiles that have been glazed? I don't care if the
stuff is corrosive, as I can always dilute it, but if it's toxic (e.g.
Hydrofluoric Acid)....not happening. Sand blasting? Just not