On 16 June, 14:31, rpgs rock dvds wrote:
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.

Depends what it is. If it's cement-based rather than a paint resin,
then "brick acid" (hydrochloric) will shift it, but will also attack
the slabs so you need to be able to rinse it speedily.