This operation consisted in preparing the areas of lost paint to host the new wall paintings. The plastering carried out during the conservation work, which was finished in 2004, were left 3 to 5 millimetres below the level of the XV century paintings. The plaster had to be raised to the same level of the original paint layer, thus allowing a perfect match of the old paintings with the new ones.
The plaster was executed using a mixture of 2 local clays, shi-sa and shi-pi-pema, mixed with a solution of 30% vinyl binder. To strengthen the plaster and reduce the risk of cracking while setting, very fine chopped straw was added to the mixture.
In some areas the old plaster had to be removed because of humidity issues, thus creating a deeper gap to be filled with plaster. In those cases, chopped straw was added to the plaster mixture so as to strengthen it and reduce the cracking of the plaster while setting.
Once the plaster was set, a whitewash of tung-sa, a local kaolin based white clay, mixed with an 8% solution of acrylic binder in water was spread homogeneously by brush. After drying, this coating was smoothened by using different mesh sizes of sandpaper.