I have a 70s building with radiant heating in the ceilings (bedrooms & living room). There is that popcorn junk on top of the radiant heating and the assumption is asbestos. We want to have smooth ceilings. I do not want to attemp to mess with the popcorn for numerous reasons. The Question Is: What can we use to skin coat or add on top of the popcorn to smooth it out and not affect the heating of the radiant? Or affect the material that will be placed ontop of the popcorn? Spackle? Any suggestions?