Everything is about connecting the plaster with the base, you cannot apply a stronger material over a weaker base, this will tear it down. For softer walls, use gentler and softer materials, for stronger walls use some tougher materials. Lime is fire ‘aag’, violent and ferocious, the earth is ‘mitti’ gentle and calm. Fire will tear the earth, so applying the strong lime over the weaker earth base may not be the best idea, however, you can mix lime to mud to make it blend better with the base when you coat over earthen walls. Also, cement plasters are a big NO, because they are a lot stronger and will not work with softer earth walls. Understating this basic principle is very important when dealing with lime which comes with no recipe.