Cob propotions

Hi all,I would appreciate any input relating to sand / clay ratio for rocket mass stove cob.
I am using a basic red clay,the type used for very basic earthenware crockery here in Portugal.
The sand i have is coarse from an inland source (not sea sand)
So far i have used 33% sand and the rest is clay,but plenty more to do.
Thanks a bunch ................. Martin J

Hi Martin; All clay is different, you should make bricks with different amounts of sand in the mix., dry them out and see how strong each mixture is. Normal mixture of cob is 3 parts sand to 1 part clay. everybody thinks that cob is mainly clay with a little sand mixed in, but it really is sand with a little clay mixed in to hold it together. tom

Thanks for taking the time to reply Tom...Martin