Hi Mathieu,

No, cement can not be incorporated and be stored because it's process of setting is different from lime setting. In cement water activates the reaction (setting) in lime water prevents the reaction(setting).
In lime putty carbon monoxide in the air activates the lime. In lime plasters water prevents carbon monoxide from reaching the lime.

On the interior wall you need cement only in the scratch coat. You should use white portland cement and you can use hydrated (dry) lime for the mix type N

About sand: It is important for the sand in lime plasters to be angular not round since the layers must "have a tooth" to "stick" to each other. I believe that you can get volcanic "tuff" (i do not know if this is the right word) in Hawaii. You can use it instead of sand, in Italy it was often added to sand
for better "tooth" and at times sand was not used at all, for intonaco they used "marble dust".

About sand being "guaranteed" to be without salts - do you want to experiment to prove their guarantee?
I am skeptical about that - why do you wash sand?
To get read of organic particles and dust - solids that are lighter than water. When sand is being washed those particles float on top and you remove them (sand falls to the bottom). Salt dissolves in water and you need a river of it(water) to wash it away.

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