Can I hang Wallrock Thermal Liner on ceilings?

Yes, but before applying Wallrock Thermal Liner,  you must lightly sand the ceiling and size with a PVA or Flake Adhesive. This will form a good surface for the Thermal Liner Adhesive to adhere to.

With Wallrock Thermal Liner, how do I tackle external corners?

Well you have 2 options – Wallrock Thermal liner will bend around the corner and this will give you a rounded corner, alternatively you can cut and butt joint at the corner, this option is best if you are applying a Wallrock Lining Paper or Wallrock Textured paper on top as it will hide the joint.