I think oven mass needs to be brought back up.

[asudavew]

In the following thread Dmun raised some valuable questions about oven construction, more specifically the overall mass of the oven.

I wish I would of found this one before construction....

If I had to build my oven again, I would probably opt for thinner walls and more insulation.

I'm putting a link to his original thread, because I think it might be of value to new builders and it needs a bump up!

http://www.fornobravo.com/forum/f8/p...thick-215.html

Happy Reading,

Dave

[RCLake]

Re: I think oven mass needs to be brought back up.

Dave
I think you have hit on a great historic moment. The pioneers of this forum. They not only challenged conventional wisdom but established a forum that have given us hope and inspiration to build our own WFO. I first wanted only a smoker to do BBQ and came across the bread making oven - the barrel type with lots of cladding and was sold. Finding this site, I was skeptical, it wouldn't keep its heat. It didn't take that long until I was sold on the round oven. So thank you, the pioneers of this forum from 2005.

By the way Dave, do you have to much time on your hands to find this historical background?

[Ken524]

Re: I think oven mass needs to be brought back up.

Dave,

That's an interesting thread. You've been firing your oven pretty regularly now. For what reasons do you wish you had a lower mass?

Sounds like I may be glad I didn't add a coat of mortar to the outside of the dome.

[asudavew]

Re: I think oven mass needs to be brought back up.

Dave,

That's an interesting thread. You've been firing your oven pretty regularly now. For what reasons do you wish you had a lower mass?

Sounds like I may be glad I didn't add a coat of mortar to the outside of the dome.

Well... mainly it's the heat up times and the amount of wood required.
it can take upwards of 1.5 to 2 hours.

I think it would be nice to fire it up in 45 minutes....
Now on the other hand... I do have really good heat retention for the next day.

Trade offs... Just life I suppose.

Maybe I will have to build another....!!!!!! Low mass.

So I can have either/or.!
Now I may be on to something!

DAve

[asudavew]

Re: I think oven mass needs to be brought back up.

Dave
I think you have hit on a great historic moment. The pioneers of this forum. They not only challenged conventional wisdom but established a forum that have given us hope and inspiration to build our own WFO. ?

I appreciate them everyday!

By the way Dave, do you have to much time on your hands to find this historical background?

Actually, I'm an accountant for an electric utility.
At the first of the month I am busy closing the previous month's books.
That usually takes 2 weeks.
The last two weeks of the month, I am looking for anything to do... Hence my fascination with Forno Bravo.

I did get a promotion .. effective on April 1st next year. So I may not have as much time... but until then.. I guess everyone is stuck with me!

How's the build coming along for you?

[Dutchoven]

Re: I think oven mass needs to be brought back up.

Dave
This topic has been discussed several times and i think it will come up many times more. It was briefly mentioned on that thread about structural stability when using thinner walls. Less mass less time to heat up yes but, brickwork has to be spot on because the line of thrust has to fall within the inner 1/3 of the thickness of the brick...on a 2.5 inch thickness that leaves only a little space. I suggested on an earlier thread(one that I can't find right now) that the lower courses(1-3) be comprised of 6 inch units created, then through the middle courses go to the bricks cut in half 4.5 inch units and then the last 3 or four courses go to 3 inch units. This design would load the haunches of the dome and thin out the upper level of the oven to(in theory) shorten heat up time. As for thickness of the floor, to me it would be a personal choice...my oven floor thickness is about 4.5 inches...pompeii plans give you 2.5 to 3 inches the other option is brick splits which are 1.25 inches and will on average cost at least double what a standard firebrick is(that is what it was here $1.02 versus $2.08 per)
Dutch

[dmun]

Re: I think oven mass needs to be brought back up.

I have a really low mass oven. It's composed of bricks set on edge, or a 2.25 inch thickness. I have a lot of insulation, but it's not of uniform thickness, because I designed a couple of voids through the oven enclosure for another purpose. As I stated in the thread you dug up, I wanted just enough thermal mass to cook a turkey, and just last month I passed that milestone with flying colors.

In the end, I decided that the thin oven was going to work because it was the same thickness as a pre-fab oven. Building an oven that thin requires some finesse, and might promote cracking, but I'm now convinced that almost all ovens crack. I have a bunch of hairlines, but I didn't stress about it because all my bricks are angle cut, and couldn't fall in short of an east coast earthquake.

Remember that when I started researching this, the vermiculite layer was BELOW the support slab, which you heated up in its entirety everytime you fired the oven. I read about paulages pouring his entire winters wood supply into the oven trying to get it up to temperature.

Now most builders use cal-sil or ceramic fiber block directly under their cooking floor. Right there you have a hundred percent beter insulated oven than that first generation. If you ask me now, I don't know if the thin dome is worth the extra work. How fast your dome is ready for pizza is a function of a bunch of things, including how good and how dry your firewood is, and what the exterior temps are. In any event, I'm glad I did the geodesic dome. It's neat to look at, and impresses folks with how crazy I am.

[RTflorida]

Re: I think oven mass needs to be brought back up.

Interesting.
I'm taking the lazy approach in asking (I don't want to go back through your entire oven building thread) "how thick is your dome"?
I did the standard 1/2 brick thickness with 1/2"-3/4" mortar cladding before insulation. It has never taken more than an hour to go all white. This past Sunday morning I fired it during the coldest (sorry it really doesn't get cold here in Tampa) and windiest conditions yet - 45-50 degrees and 20-30 mph constant winds, and it was still white in the usual 45 minutes and equalized within the hour. Must be my 2" blanket and 3 1/2" of perlcrete.
Are you sure you are not losing heat from going a little light on insulation? Just a thought.

RT

[Frances]

Re: I think oven mass needs to be brought back up.

This is an interesting thread!

...a couple of days ago I mentioned on another thread that I'm glad not to have added any additional mass to the outside of my oven. The half bricks are quite enough to go along with.

When I heat my oven its really great for pizzas, gets white quite fast (under an hour), but then tends to equalise at at around 190 C (375 F), which is not really enough for bread etc. At the same time I think the insulation is quite impressive, because two days later with below freezing temps outside the oven is still at 50 C (over 120 F). So what it needs is longer heat up times. From what I've heard, Dave's insulation is even better.

Which is fine, all I'm saying is the oven certainly doesn't need MORE mass (which has also been discussed a lot recently). If in doubt, leave the cladding out.

On the other hand, after reading this link (which Hendo originally found), I wouldn't dare go with thinner walls. It may be an advantage for experienced or gifted builders, but certainly not for me...

Auroville Earth Institute is a research, design and developing agency for vaulted structures, construction of various Vaults, Arches, Domes (VAD).

[dmun]

Re: I think oven mass needs to be brought back up.

On the other hand, after reading this link (which Hendo originally found), I wouldn't dare go with thinner walls. It may be an advantage for experienced or gifted builders, but certainly not for me...

Auroville Earth Institute is a research, design and developing agency for vaulted structures, construction of various Vaults, Arches, Domes (VAD).

This is the first time I've seen that. Everyone building a dome should read that page.

At the end, there is an interesting condemnation of cement-based mortars. Of course these folks are working with compressed earth blocks, or adobe.

[gjbingham]

Re: I think oven mass needs to be brought back up.

Dave,
If I remember correctly, you bought used bricks (?). I'm wondering if you perhaps got medium or high duty fire bricks, such as those used for kilns etc. that take more heat to get them up to temperature, but hold the heat longer once there. That might explain the longer firing times but great heat retention.

George

[Dannyboyblue]

Re: I think oven mass needs to be brought back up.

It's interesting that this comes up just as I've been wondering about adding mass to the oven floor. I was specifically thinking about laying the floor bricks on their edges increasing the floor thickness from 2.5 inches to 4.5.

I was thinking about this because I have notice several posts where people mentioned that the floor quickly lost heat. I was wondering if the pizza itself sucked heat out of the floor, and if each subsequent pizza should be made on a different part of the floor to allow the previous floor section to re-absorb heat reflected from the dome.

So would a thicker floor hold heat longer and would it be so thick that the fire time would be to long?

I notice that Dutchoven was also thinking along these lines,

Less mass less time to heat up yes but, brickwork has to be spot on because the line of thrust has to fall within the inner 1/3 of the thickness of the brick...on a 2.5 inch thickness that leaves only a little space. I suggested on an earlier thread(one that I can't find right now) that the lower courses(1-3) be comprised of 6 inch units created, then through the middle courses go to the bricks cut in half 4.5 inch units and then the last 3 or four courses go to 3 inch units. This design would load the haunches of the dome and thin out the upper level of the oven to(in theory) shorten heat up time. As for thickness of the floor, to me it would be a personal choice...my oven floor thickness is about 4.5 inches

Dutch is your oven finished? Are you happy with your floor thickness?

[james]

Re: I think oven mass needs to be brought back up.

It's interesting that this comes up just as I've been wondering about adding mass to the oven floor. I was specifically thinking about laying the floor bricks on their edges increasing the floor thickness from 2.5 inches to 4.5.

There is a lot going on in this thread. :-)

First, for those of us who have been doing this for a longer time, the question of whether a 4"-4.5" thick round oven dome has too much mass, not too little mass, is validation that we are doing something right. When I started FB, the only resource available in English was the Bread Builders, which describes a 9" thick dome and 9" thick floor. I built it, saw the problems, and started writing about it -- and caught a lot of flack. Some of it pretty nasty. It was as though I was criticizing a cultural icon.

So let's enjoy the moment to appreciate breaking through that problem.

In terms of the question, I believe that a 2"-3" dome and floor are perfect for home cooking. They heat up quickly, hold high heat (that is critical -- more to come on that), and they hold more than enough heat to bake and roast anything you want to cook. The FB residential ovens are all in this range, and they are the real deal; made in large volume in Italy and used by huge numbers of home owners.

One other note. Commercial pizza ovens, hot 365 days a year, are about 4" thick.

The issue with the floor, and to a less degree the dome, is keeping it hot by recharging it with your fire. A thicker floor actually makes it more difficult to maintain high heat -- because the thicker mass will wick heat away from the oven chamber to the outer mass of the floor. Definitely stick with the brick on its thin side for the floor.

Here is a copy of the Holding High Heat graphic.

Hope this all helps. Great topic! :-)
James

[Frances]

Re: I think oven mass needs to be brought back up.

Auroville Earth Institute is a research, design and developing agency for vaulted structures, construction of various Vaults, Arches, Domes (VAD).

At the end, there is an interesting condemnation of cement-based mortars. Of course these folks are working with compressed earth blocks, or adobe.

...hmm, I didn't notice that bit. What exactly are they saying, why are cement-based mortars supposed to be a bad idea?

[Dutchoven]

Re: I think oven mass needs to be brought back up.

I agree 98% with James, the other 2% I still agree but with a little reservation. The oven I constructed is of a Scott style. The brick are laid on edge and therefore 4.5 inches plus concrete of 3 inches for a total of 7.5 inches and the walls and dome are 4.5 inches of brick plus 3 inches of concrete for a grand total of 7.5 inches. It is a lot to heat up. I like James deal with the drawbacks. 2 to 3 inches with lots of insulation is PERFECT in my very humble opinion. Now for the reservation, comes the same as in my last post. For amateur builders like most are constructing a structurally sound dome with only a 2-3 inch thickness is a difficult process. The modular ovens are made to fit together and be structurally sound. So in truth I am 100% behind James on this.
Dutch