This is urethane rubber (Smooth-On Simpact 60A) applied to plaster tape and Li-Qua-Che (Activa).
Appearance: Added a rubbery, glossy appearance. It also made the Li-Qua-Che appear much more yellowed and cracked below the surface of the rubber while it cured.
Physical changes: The surface is much more grippy and even a bit sticky.
Utility: Adds grip, waterproofing, and strength to the form.
The addition of the urethane rubber makes the appearance of the surface more unpredictable and feel more finished.