I do have experience with exterior earthen plaster and exterior lime plaster. I have a cob house with an attached strawbale walk-in cooler for our farm. The strawbale cooler has cob infill, then earthen plaster, and then lime plaster. It has been mostly done for 2 years, and even though there are some areas that still have only one coat of lime plaster, they are wearing very well. I can see no evidence that the earthen plaster substrate is stressing the lime plaster. The base coat of lime plaster was supposed to be covered with a finish coat all over, but is still only half done, as it has been so patiently showing no wear, that it keeps falling down the priority list. However, I will say that the wall that has the second coat of lime plaster looks so beautiful that I do intend to add the second coat everywhere. Then, the general maintenance plan is to "whitewash" it with thin lime solution every few years. Earthen plaster is generally more forgiving and easier clean-up, but the weatherability of lime was important to me over the strawbale, as I have fear of moisture seeping in during driving rain. I do love plastering, and am now in the process of plastering over my outdoor cob oven. With a good amount of screened horse manure, the earthen finish plaster seems to wear as well as lime. One can always oil it for even more durability. Then it is basically the same as the finish coat of my earthen floor, which baffles me with its durability. However, the lime plaster is literally rock when fully cured in moist conditions, so is even MORE durable than well-prepared earthen/manure plaster.