I can't remember seeing anything about this within either the main book or the IH.

Does daemonic toughness count against force weaponry? I'm of the opinion that as a psychicly powered attach it doesn't but is it in the RaW anywhere?

I don't think there is a quote, but I'm quite certain I'd run the rules in this way: As long as the weapon benefits from the extra damage due to the wielder having a psy-rating, the weapon will ignore demonic toughness. If it is wielded by a nonpsyker, near a null-rod or in any other situation where psychic powers are not available, its damage will b ereduced by demonic toughness.

It's damage from a psychic source, so it's not thwarted by Daemonic.

zethliss said:

Daemonic entities do not double their TB for damage inflicted by force weapons [DH core, p. 329].