Soil composition for the Press

Greetings. I am very interested in the CEB press for producing Compressed Earth Bricks to the same dimensions as standard fired clay bricks. I wish to know however if it is possible for a normal mud brick that is pressed in the machine to have similar properties to the clayly ones that OpensourceEcology produced for the micro house?

Getting soil appraised for clay content isn't a problem for me as I am a geology student, however I wish to know if simple mud is a good idea for a insulating, structural brick. By itself or by addition with lime mortar. Thanks for the help.

Best regards,

David