It is hard to get sand with out salt, so I guess we would have to add cement, other wise we will have too much clay in the mix.
How do we determine the clay, sand, cement mix?
There is a special cement (ASTM type II) that you can use for areas with a lot of salt in the environment. Here is Cemex's explanation of ASTM cement types. Cemex is a major producer of cement. Here is Cemex's Nicaragua site.
A good book for developing mixes is Compressed Earth Blocks, Volume 1, Manual of Production.