Sorry if I've misled you - but no, you have to mix it on a clean surface (I use a piece of smooth scrap ply) the idea of the dual tubes is that, when you squeeze the plunger you get equal quantities of resin and hardner. This you then mix to a consistent colour (sort of a pale off-white) using a spatula of some sort.
It can then be applied to the joints...
I use the 30min stuff to give me time to make any adjustments as required.
Hope this helps.
Regards,
Ray.