ORIGINAL: johnvb-RCU
I've been using baking powder (what we call it here in Oz) with cyano for quite a while. Works good, but I wouldn't call it easily sandable. I mostly use it where it can't be seen. Works well to build up a fillet to add strength, especially on repairs.
Baking soda and Baking powder are basically the same. Powder has a "dry acid" included with it, to sort of slow down the reaction.
Baking soda requires a "wet acid" and releases all its by product (ie: CO2) all at once, which I think is what we're aiming for with this tip.