The builder and others also call it Adobe Bag and Superadobe construction but I'm not sure you couldn't use any clean dirt, either moist or dry. Nobody went into any detail on what constitutes Adobe ... as in; mud, clay, straw, fiber, etc. Lot's of sites and pages on this kind of construction "out there" so we'll find the best answers when the actual time comes. Personally I'd love to buy an adjoining lot to mine and experiment with things like this and a real vegetable garden.
The casita builder below has a screen name of Mazinka and lives in or near La Manzanilla north of us in Melaque. He just suggested that the fill earth should have a certain amount of clay and sent this link - What is Super Adobe . The video on the bottom just has some ideas for something similar but I much prefer the palapa roof and other local ideas. Stucco or mortar directly to plastic does not sound secure and I would definitely try to attach chicken wire like they do on old Adobe restorations.
