Damian,

Even the "no blush" epoxies produce some blush, and they don't have to be fully cured to have it on the surface. So, even when coating on green epoxy - not tacky but soft enough to dent with a finger nail - if you're not sure about blush, its not a bad idea to wash the surface with a wet rag or soft scrubber. Just make sure that the surface is dried thoroughly before coating. A heat gun or hair drier works well.

Sam