ok, so its raining, I'm part way through a jetwash-the-patio project and I like science.
Kiln dried paving sand is approximately £5/bag; Dansand is approximately £9/bag.
Dansand are a bit coy about how it works saying 'Dansand® joint filling sand consists primarily of common quartz sand from Denmark and sustainable natural minerals that give a high pH value. If you have first used Dansand® joint filling sand...between your stones, you do not have to work as hard to combat and burn off weeds. You can say goodbye to a lot of unnecessary chemicals.'
The data safety sheet says 'quartz' and 'sodium silicate'. A little research reveals sodium silicate aka waterglass is a white powder that dissolves in water to yield an alkaline solution (high pH value checks out). As the water evaporates, the solution solidifies into a glassy solid (I guess this glues the sand particles together keeping them in the joint, keeping dirt out, and preventing root establishment).
However, the data sheet states that Dansand is insoluble; can an insoluble mineral change the pH? And other sources say high pressure and steam is needed to dissolve sodium silicate to make waterglass. So will it work?
I'll report back in a year.
Cool fact: Placing freshly laid eggs in a water glass solution seals the pores of the eggs against bacteria and gases, so it can be used to preserve eggs when refrigeration isn’t an option. This is not an approved application of Dansand.