Cob is amazing stuff. It's so strong you can sculpt it out from the wall to create shelves and benches that project into the room (this is called a cantilever). Built-in surfaces for storage and seating maximize your interior space. Make yourself a beautiful window seat by cantilevering a bench out at the bottom of a big window. When you build indoor furniture consider the final floor height, so the seats are at a good position. You can copy the measurements and angles of one of your favorite chairs or couches to help you create a comfy seat. If you want a wide seat or shelves, you may want to build up the thickness of the wall or foundation under the cantilever before you start sculpting it. This will save you time because making a cantilever is time consuming, careful work.
Add extra straw and clay to your cob mix for cantilevering. Build out a little at a time, leaving a rough holey surface. Let it dry enough to support itself before adding the new cob.
Take extra care to make sure the new addition is well attached to the last cob. Cantilevering takes patience and a little practice. Sometimes the cantilever falls off. Don't panic, keep at it, just add on a little slower. You can stick little sticks or straw into the cantilever, sticking out into where the next cob will be added. This will help hold the weight until the cob hardens and add to the tensile strength.
If you use something to temporarily hold up the cantilever while it hardens, like a bucket or straw bale, make sure you remove it within a day, or it'll get stuck as the cob dries and shrinks.
You can always chop away furniture and shelves if you decide you don't like them later on. It's possible to add cob furniture after the building is made, but it will be easier and stronger to do it as the building grows.
Fireplaces can be sculpted out of cob. Fireplaces are very beautiful and romantic, but not very fuel efficient. The Earthbuilders Encyclopedia has blueprints for a fireplace and lots of tips for adobe brick fireplaces that can be easily adapted to cob. See the recommended reading list at the back of the book.
I suggest doing some reading to get an understanding of the basics of wood stove efficiency. A metal wood stove and stovepipe can be surrounded by cob, leaving access to the door of course. It's a good idea to insulate between the hot metal and the cob with vermiculite or wood ashes. The insulation insures that the fire will burn hotter and more efficiently. After the heat gets through the insulation, it will be stored in the cob, radiating heat into your house after the fire has died down. Stoves can heat up cob benches for toasty bum-warming seats. In many countries, the stoves and pipes are all made out of cob. See the 'Books to Read' section (page 173) for recommended reading on masonry (cob) stoves.
Cob is a medium that invites sculpture! It's super flexible. You can make relief sculpture as you cob. You can also make artistic dips and holes in the wall. Or you can cob a bulge onto the side of the wall and when it's hardened a little, carve it to the shape you want. You can add a sculpture to a dry wall if you rough it up well, re-wet it, and add some nails pounded part way in to help the fresh cob stick. When adding large sculptures to an already dry wall, use large nails. You can add one part mushed up newspaper pulp to one part cob to lighten the weight.
If you decide you can't live with your sculpture or you want to change it,
go for it. One of the wonderful things about cob is you can chop and change