We live in a house with an original cob section that was extended with rendered block work extensions during the 1980s and 1990s. As a result, the external face of the front if the building is a cob wall and the former cob external walls are now internal walls.
Before the extensions were added, the house had been rendered with a cement based render and the internal faces of the walls had been plastered with gypsum or cement plaster.
We had the external render on the front of the house removed and replaced with lime render.
My question is: is it necessary for us to remove the existing plaster from the internal faces of the cob walls and replace it with lime plaster or can internal cob walls reasonably be left covered with cement or gypsum plaster surfacing?