I am new to this page, however, have cooked in a brick oven many times before.  Now I am building one.  I am attempting to do this as green as possible.  I have had the city dump sidewalk in my yard for the base and am now researching the use of cement vs fire brick for the oven floor.  I have left over red brick from years ago I plan to use as the dome.  The idea is to recycle as much material as possible and keep the build cost to a minimum.  I am wondering whether I could replace fire brick ($$) with cement for the floor.  To eleminate, or rather, decrease the possibility of natural expansion and contraction I have thought of pouring in sawdust or shavings in with the cement as an additional ingredient; technique is very similar to a cob oven.  Any advice out there would be helpful.  Thanks

Russ