Thanks for the replies, all very informative.
I'm naturally suspicious of alternatives to tried and trusted methods. I once ballasted some track with Johnson's Klear to see how that performed after hearing it's virtues extolled on RMWeb and it was a disaster, the stuff just would not set. You could remove the ballast with a slight touch of the finger.
Because my layout is portable I need things that are glued down to stay stuck, no matter how many knocks they get. I will stick to ballasting with diluted PVA as I've never experienced a problem with it.