i was fortunate to meet a couple who built a adobe house in West Virginia, they raised 3 kids in it and 30 years later are still happy with it, adobe floor included, there is a arguement in the passive solar arena about insulating under floor or not, it is my opinion not to as ground temp can help in cooling and heating, a perimeter insulation being blueboard or like dug in with a mattock 1 foot or more is good, to clarify the terminology(adobe),the man told me he made block with a form 18"x 30"x8", he said it about wore his ass out