But it set me wondering:
What conditions exist once I've spread it on the wall that don't exist in the tub, so that it remains gloopy in the tub, yet sets solid on the wall?
Is it contact with the air?
In the tub, there's a plastic film over the stuff, but there's a substantial volume of airspace in there too. There wasn't a mega-vacuum-sook when I removed the lid.
Or contact with moisture in the air?
Is the air volume in the tub super-dry?
Either way, I larded the stuff on fairly thick ( say 3mm ), and so I can't see how I fully aerated the full volume of material I placed on the wall. So the setting mechanism ( if its based on contact with air ) needs to propogate from the briefly-exposed surface through to the unexposed interior. So why does the whole lot not set in the tub by the same mechanism?