. The bath, which is coated with white marble, is 12 feet 10 inches in diameter, and about 3 feet deep, and has two marble steps to facilitate the descent into it, and a seat surrounding it at the depth of 10 inches from the bottom, for the purpose of enabling the bathers to sit down and wash themselves. http://www.ukans.edu/history/index/europe/ancient_rome/E/Roman/Texts/secondary/SMIGRA*/Balneae.html
Finishing Design Standards, Example #10 . . . Finishing, 4. Stone and ceramics applied on the interior shall have not less than 1/4″ cementitious backerboard for vertical surfaces and not less than 1/2″ cementitious backerboard for all other surfaces, in either case applied over a moisture impermeable layer or membrane.
Policy: Wood is an unsuitable substrate for masonry. It’s not stable enough with variations in temperature, moisture, and forces – particularly compression forces.