Stuart Noble coughed up some electrons that declared:

Use it for whatever you like if you know its properties. I'm sure there
was a time when pva was only used as an adhesive.

That's the nub of my query: what are it's properties?

Does a bit of it by itself set solid like PVA? PVA has limited gap filling
properties so it clearly makes a good binding agent. Ordinarily I'd just
pour PVA into dodgey cracks and holes, but knowing it will be exposed to
continuous damp, I've seen warnings on this group that it will dissolve
into squidgey gunk.

Unfortunatly SBR isn't the sort of stuff I can get 100ml from B&Q to fiddle
with, I'll have to bite the bullet and get 5l, or 25l from the builders
yard.

I was hoping that someone had played with it enough to give me a lead, but
if it comes to it, I'll get 5l and try some stuff.

Cheers

Tim