In article ,
rpgs rock dvds writes:
Big puddle of white stuff on patio, next to fence. Workmen next door
appeared to have emptied their slops through fence on to our patio.
Tried white spirit, soap water, white stain goes away but when the
area has dried, it "reappears". Not 100% sure what it is, thought at
first was paint, but could be something worse, like a type of cement.
Any idea how to shift it please? (Did think of pressure washer, but
we'd have to hire one.) Neighbours aren't around to discuss prob, as
building seems to be empty - prolly to be put up for let sometime
soon?

If it's cement, you want brick acid (hydrochloric acid) to dissolve it.
Actually, you could try any medium strength acid on a small bit just
to confirm if that's going to work -- I have used kettle descaler.
Wet it with the acid, and leave it to work on the cement for a bit,
and then see if it will brush off. Wear appropriate protection.
Could be plaster (better fits your description), and that will also
come off with brick acid (even more easily than cement).

Brick acid dissolves (or marks) other things too, such as pointing,
and maybe even some stone, so be careful.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]