WFO construction questions

I've never built a Denzer-style oven, but some generalities:

Generally, the heavier the material, the better it can absorb heat. Personally, I used about 3" of concrete under my hearth brick, with about 4" of insulation under the concrete. That way, it absorbs a lot of heat, but radiates it into the oven instead of out to the cook's feet. But that may not applicable to a Denzer oven since a the deck of a Scott oven is suspended on rebar. (Dunno if the Denzer plans would allow for using insulation under the deck.) The thing that worries me about clay is that it expands & contracts a lot if it gets wet, so your floor may have some issues if it gets wet. I'd worry about using clay if the oven isn't well out of the elements. But like I said, having never built one, this may be way off.

Door size is always a trade-off. Smaller is better for the oven, bigger is better for the baker. Find a happy medium based on your own planned use.

ClimbHi
Pittsburgh, PA

You want a good insulating layer underneeth the hearth floor.  Ordinary concrete will work, however, it will initially pull heat away from the hearth and oven.  Granted, if you fired for a long time, this will provide a large heat sink and keep the oven hot for a long time.  It will take a fair amount of wood to get there, though.  Many of us have opted to pour an insulated concreate layer (portland mixed with perlite or vermiculite) under the hearth (fire brick) floor.  This slows down the heat transfer into the base.  Specialized insulating boards can also be used.  Fire brick itself can also be imbedded into the concrete base under the actual fire brick hearth floor.  I ended up with a 6" thick reenforced regular concrete base.  I poured 6" of the "perlcrete" on top of that.  Following that layer, a thin layer of fireclay was spread (like laying tile) into which the hearth floor was set.  The floor is actually loose, not cemented down. 

Be careful on the door size.  If it is too large, you will have trouble building up heat, as it will escape through the door.  On my Pompeii, I think I have it about 18" wide and 12" tall.  I don't recall exactly, but it was dman hard to crawl into :-)

Let us know how it comes out!

I have few pictures (in need of updating!) at:

http://pdiff.weebly.com/oven.html

You might also want to search through the forums at Forno Bravo for recommendations on floors and doors:

http://www.fornobravo.com/forum/

my oven yet, but it will not be a small one, you can always place baffles of brick into an oven to make the space smaller, but its darn hard to enlarge it so build it bigger and fix the space after! As to the door, I have just bought a super peel, which I beileve is about 14-16 inches wide, so the door needs to be wide enough to pass this through. Not to mention I have a 14 inch cast dutch oven which is about 8-10 inches high to use in the oven, so the door must reflect what you will be using to place your breads, or any impliments and pots you might wish to place in said oven.

As to the sand versus clay, personally I will go with the sand, because of the ease of replacing or releveling the hearth in future, I am going for a larger oven, because I have thoughts of possibly baking for sale in the future, but also because I want to be able to use it for other things than just baking bread, and a larger oven will retain more heat for longer slow roasting of meats and longer bakes of less high heat items like buns and specialty loaves etc.

I am about halfway with my oven. See the blog here http://www.thefreshloaf.com/node/17057/building-earth-oven.

My floor consists of a wine bottle and sawdust/clayslip mix of about 4" and then there is a slab for the heat sink on top of that.  My door is 10" high and 16" wide. I finished the first clay layer of the dome and I am planning to test it first. I have not been able to light a fire, so I cannot say how well or not it has worked. It has been raining cats and dogs here.

Will try to update the pictures tonight.

Regards

Willem