Wood fired oven questions - Contractor Talk - Professional Construction and Remodeling Forum

**joasis** · 02-08-2010, 07:08 AM

Ok...you guys got my curiosity running full blast. I have studied a lot of web sites, and bought a guy's dvd on how he did his own oven, but I still have questions.

1: Is it necessary to actually float the hearth base, or could it realistically rest fully on the base?

2: If firebrick are used on all of the hearths, and there is a concrete base under this, then why the added vermiculite and cement board?

3: Is a dome better then a barrel vault, and is a dome that hard to do?

4: I am not a mason, so some of this is not common knowledge for me, like high heat mortar, and if it can be made, can the hearth be made from a high heat concrete, and then do not use the firebrick? Can the dome be made the same way?

5: Is there a reason vermiculite is placed over the dome or barrel? Is this to break the thermal bridge and help the oven retain heat more effectively? How about using mason's sand between the dome and outer shell or box?

That is it for now, but if there is a book, give me title....thanks guys.

dakzaag · 02-08-2010, 07:45 AM

Joasis,

I have been reading up on the same stuff. I am sure TS will fill you in better, but from what I have read, the key to getting your temperature up into the 700 degree range quickly is to have lots of insulation.

If it takes three hours to get the oven hot enough to cook with, how often will you realistically use it. I watched a video where the guy lit a fire and in 35-40 minutes he was ready to cook a pizza.

Less wood is needed to get going and I suppose less ash and waste when your done.

From the pic's I have seen you can either cut and fit the brick for the dome and use just a little refractory cement like a normal fire box or just build it out of halves and use a lot of cement to fill in the gaps.

Some of the ovens look pretty sloppy when finished, but after a few fire's you can't tell the difference so I am not too sure there is an advantage of multiple cuts on every brick just to maintain an eigth inch joint.

Looking forward to more experts chiming in on this one.

Tscarborough · 02-08-2010, 07:47 AM

The oven works by absorbing and retaining heat. Thus, the idea is to have a certain amount of mass and to isolate and insulate that mass. Castable refractory is not really hard enough to use as a wearing surface.

The dome may be marginally better than a barrel vault at directing heat back to the cooking surface, but it is also almost impossible to build without unacceptable (to me) sized joints.

tcleve4911 · 02-08-2010, 08:59 AM

sorry wrong post.............

**joasis** · 02-08-2010, 10:28 AM

So Tscarborough, how about a step by step tutorial, with explanations? I bet I am not the only interested party here.

cannyfradock · 02-08-2010, 10:52 AM

joasis

I have built a pompeii-style wood-oven and know a bit on wood-oven building, although Tsacborough sounds like he know's a lot more on the subject.

But we are both members of... http://www.fornobravo.com/forum/
which has everything you would ever want to know about any type of wood-oven. You can also download free plans on wood-oven/dome construction. You may have to register and put it in your "to buy" trolley....but they are free.

Terry (C.F)

Tscarborough · 02-08-2010, 11:25 AM

My knowledge is general masonry. This is the first oven I have actually built, but it is pretty straightforward.

Leaving out the stand and the decorative aspects, it goes like this:

Place a 4" layer of 8-1 perlite/portland on top of your stand.
Mortar set firebrick in a running bond or herringbone at 45 degrees to the entrance of the oven. Cut the Fire brick fit the footprint of the oven.

Build the dome/vault using falsework or mounded sand.

The only important aspects of the dome/vault are to have a final dome thickness of around 4" and to make the entry opening around 62% of the height of the dome.

Cover the oven with either insulating blankets ($$$) or another 4" of perlite/portland mix or build an enclosure and fill it with loose perlite (what I am doing).

That is all there is to it.

dakzaag · 02-08-2010, 12:48 PM

Joasis,
I am really interested also. I have followed TS progress as he posted pics of his new project. Nice work by the way TS.

While snooping around over on the forno website, I found a guy who had a whole bunch of pics of his oven. Here is a link to the pics, he left it open to view I suppose. If not, well the cows are out now and a little too late to close the gate.

http://picasaweb.google.com/chrisbme...zzaOvenProject#

I am trying to figure out how to incorporate it into an outdoor fire place on my porch.

Tscarborough · 02-08-2010, 01:06 PM

Mine is crap. That guy built a nice oven.

cdkyle · 02-08-2010, 01:31 PM

Just looked at pics. Hey, I'm sorry, but that guy really had it going on. Until, in my opinion, he started with the metal frame and roof thing. That just does nothing for me except cheapen a fine piece of work. Why didn't he just go ahead and finish the dome out of masonry?

Tscarborough · 02-08-2010, 01:46 PM

It is all masonry. They use steel studs to be fireproof, but to me, if it gets that far, burn, baby burn. The only thing I don't like is the metal chimney.

**joasis** · 02-08-2010, 04:38 PM

So, is there any reason a course sand would not be a good insulator? Also, the link above looks like hat guy did not build a "floating" hearth slab?

Tscarborough · 02-08-2010, 05:04 PM

Sand would add to the thermal mass, not increase the insulation.

He has a 4" concrete slab and 4" of perlcrete on top. (photo 5)

natural1 · 02-08-2010, 05:27 PM

I appreciate all the time, skill and effort that guy put into his oven but too many different materials. I find it tacky.

I need a new project for my house and am considering a pizza oven. But then I think - that's a lot of work just to cook pizza. Wondering if there are people who build masonry smokers?

Tscarborough · 02-08-2010, 05:43 PM

It isn't just for pizza, or I wouldn't have bothered. I plan on cooking meat way more often than I make pizza, plus I like to bake bread.

For a barrel vault at least, 2 guys could knock out the oven in a weekend, no problem (from insulated slab up, that is). I am lucky to string together 4 hours on a weekend, so it is taking me a lot longer.

Rockmonster · 02-08-2010, 07:00 PM

What timing!! I have a guy who wants an oven in his backyard for entertaining, what not. He has a setup at his regular home, and he directed me to earthstoneovens.com They have some nice pictures of residential ovens. It looks like this is the next big thing....I've eaten at a place called Fore St. in Portland, ME, where most everything is cooked in a wood oven....Nothing like it...time to read up....

dakzaag · 02-08-2010, 07:27 PM

Quote:

Originally Posted by joasis

So, is there any reason a course sand would not be a good insulator? Also, the link above looks like hat guy did not build a "floating" hearth slab?

Think of the insulation like a themostat on an engine. A gas motor has a themostat that opens about 180-190 degrees to run most efficiently. A diesel runs most efficiently at a little over 200 maybe 204. The insulation helps the oven get to cooking temp. faster by reducing the thermal mass that has to heat up, kinda like keeping the thermostat closed longer.

If the base was a solid concrete slab, that slab would draw heat from the cooking floor until the slab was 6-700 degrees which is quite a while if the slab is fairly large. By insulating the floor beneath the fire brick, the fire brick will get to cooking temp a lot faster. Same goes for the dome.

Floating the fire brick floor down simply allows you to get a good level floor so the peel (pizza spatula) can slide in without problems and ashes don't get caught in the cracks.

The fire brick floor is the cooking surface! Most of the heat for the floor comes from the heat reflecting off the dome and heating the floor.

**joasis** · 02-08-2010, 07:44 PM

My thinking was simply that sand is a decent insulator and perhaps, the floor could be poured directly on the sand, and after the oven is mortared, sand could cover the dome, or between the dome and the outer containment.

Still thinking in learning.

Tscarborough · 02-08-2010, 07:59 PM

I am no physicist, but the way I understand the insulation is like this:

There are 2 types of insulation. One, like foam, simply blocks the transference of heat, and it does so with a minimal amount of mass. Thus, it does not store heat.

The other type of insulation works by absorbing heat with a lot of mass. Masonry structures are an example of this type of insulation.

For an oven, you want both types: A masonry shell that has enough mass to absorb and radiate heat, but not so much that it will require a half a cord of wood to get it to the proper temperature, and a low density blanket to allow the masonry mass to maintain the high temps with no more heat inputs after the initial firing.

Sand is a good insulator (so long as it is dry), but is a high mass/absorptive type insulator, and you will have to get it up to temp (which it will then radiate away).

**joasis** · 02-08-2010, 08:54 PM

Now that makes sense, totally.

So...where and how do you buy the vermiculite that is used in these ovens, and can it be mixed into a cement mix? How about lava rock?

And finally, what did they use on these ovens a few hundred years ago? Not worry about the extra fuel needed?

Since the air is a good insulator, how about pea gravel, dry? And...are the walls of the dome or vault built on the heart base, or is it intended to float inside the oven?