For underslab applications, does Volclay require a working mud slab?
No. Volclay, in most cases, does not require a working mud slab to be installed over. The reason for this is that Volclay does not rely on adhesion to function as a waterproofing membrane. Remember, a mud slab traditionally is made of weak concrete mix and usually cracks. Therefore, you are not adhering the waterproofing to the structural slab, but waterproofing the mud slab, which is typically made of a weak concrete mix and is susceptible to cracking.
