It's an aqueous solution of chalk or lime and gelatin.
A binder (this could be many different types) water , chalk or lime. Mix the chalk or lime with the same volume of water in a large bucket (first coat might need more water) you can use a paint whisk on the end of a drill to stir it, then add your binder I use a cup of linseed oil in a large bucket. Damp down your walls first then apply. Stop the walls from drying too quickly, try and keep it moist for a day. Leave a day between each coat. Hope this helps.