Skim Coat Bathroom Ceiling . Pva is ok to stabilize a friable surface and to control suction. To be sure you can use the mud before it sets, start with about a cup of powder. How to Skim Coat a Ceiling Skim coating over a textured ceiling series from www.youtube.com Use a mud pan to mix small amounts of mud at a time for skim coating. It was suggested and my code official in my town said put the time in and use the cement board. Pva is ok to stabilize a friable surface and to control suction.