"Natural mud" refers to muddy substances that occur in nature, such as wet soil or dirt, that have not been altered or created by humans. Full definition
There are hot springs, natural mud baths, enchanting islands, and several magnificent protected nature reserves including the Marmaris National Park and the heavenly blue lagoon in Olu Deniz. (loveholidays.com)
Each Hut boasts vaulted ceilings with traditional grass roofing and natural mud finishing. (greenbeltmovement.org)
That's because these areas are built on natural mud deposits, or landfill sites that are still compacting. (newscientist.com)