Reducing size inside of existing dome - can it be done?

[jwnorris]

I have a CASA110 (approx 42 inches inside diameter) that I built about 8 or 0 years ago. I love it and try to use it a couple of times a month on average. My problem is when cooking for just my wife and I, of another couple it takes a long time to get the beast up the proper temperature and uses a lot of wood for the entire process.

I am looking for a way reduce the inside dimension of the oven, either permanent or temporary? Any suggestions?

J W

[SableSprings]

Hello JW --

Is your oven under cover or is it just standing out in the bright California sun? Once cured and the insulation is dry, it shouldn't take up that much wood to bring it up to pizza temp...especially the low dome Casa2G profile. It just sounds like your insulation has gotten damp/wet. I'm assuming you are talking pizza temps here...and also really need a little more detail on the amount of wood you're talking about - "lot of wood" is a bit relative to what you're used to...and probably not what I'm used to in southern Oregon. The type of wood you're using and how dry it is will also be a big factor in the firing times and performance of the oven.

There have been lots of builds over the past years on the forum that have been cured & work well...then start having issues such as yours. Almost all of them have come back to the wood being used is too wet or the oven insulation (top and/or bottom) has gotten wet from sprinklers, rain, humidity, etc. If your Casa is outside and there are any small cracks or joints slightly open...water can easily get in and you'll have to go through the curing process again to dry it out. Check the outside of the oven for possible water entry...don't forget the area around the chimney and around the base (assuming you mounted it on a stand of some sort.

If you want a quick fix and just an occasional pizza, put a pizza stone in your oven on a BBQ grill (If the underlying hearth insulation is wet it will suck the heat out of the pizza stone.) Light a fire on top of the pizza stone and let it heat up. Simply move the coals/fire off to the side in your oven and brush/blow the stone clean. With the fire off to the side, you'll get the dome fire-roll heating and bottom heat from the pizza stone with less wood than required to heat the entire oven.

Ultimately, it should be relatively easy to fix the problem...or go for the pizza stone method

Post back with what you find out or if you like the pizza stone option. Also, including a picture or two will help everyone in spotting a problem and helping to resolve it with you.

[david s]

Fuel consumption is related to the volume of the oven chamber. If you reduce the size of the oven chamber you will be adding more thermal mass making the whole oven heavier resulting in a longer time to bring it up to temperature.
Regarding building a fire on top of a pizza stone, I tried this and the pizza stone cracked right down the middle, unable to withstand the sudden temperature change.

[SableSprings]

David, thanks for the comment...I know that it takes a special type of pottery cookware (usually expensive) that can withstand the thermal shock of putting it directly onto a hot oven surface, but I thought the pizza stone would be able to take it. The directions on most of the pottery cookware on the market in the US note that you shouldn't put it on a hot burner or in a hot oven without first slowly pre-heating it. I don't normally use pottery for cooking even at only 400-500F for that reason. When someone brings something in a pottery/clay container to heat up or cook in our WFO after the bread bakes, I ask them about how oven safe it is and normally put it on an inverted sheet pan anyway to help ease the thermal shock. That system has worked pretty well for me so far--but I still cringe putting a "strange" ceramic or pottery item in our oven.

How about starting the fire off to the side of the pizza stone and letting it heat up gradually that way? I'm not sure if it would ever get to real pizza temps, but it should work to cook some pretty tasty flatbreads. I also wondered if using some briquettes/heat beads around the pizza stone (spaced a couple inches away from the stone edges) would bring it up to temp slow enough to avoid making two smaller pizza stones

Anyway David, thanks again for jumping in on this thread...your input and insight are always terrific. Hopefully JW just got some moisture in his insulation or got some "wet" wood and he'll be back on track soon without needing to make the WFO into something else.

JW - I bow to David's experience and still think you would be best served to find out why your Casa is taking so long to heat up (when it was working well for you before...I assume). In the meantime a Tuscan grill might be an option until you ferret out the problem.

[david s]

Thanks Mike,
I was not trying to be critical of your advice, but merely relaying my experience with a pizza stone in a WFO. I'm quite sure that pizza stones vary a lot. In my case ,around eight years ago, I had the idea that a pizza stone placed in the centre of the oven would make shifting the coals and ash off it would leave a nice lean cooking surface on which to cook on. I didn't place the pizza stone cold into the hot oven , but rather built the fire on top of it. The thing cracked after it had been in for around one hour and I presumed it just couldn't cope with the heat. It was around 8mm thick and cracked into two pieces right down the middle.i haven't tried again since, but perhaps another shot could be worthwhile. I'd guess some kiln shelf would probably be a more successful solution though.
Re reading the OP it doesn't say that the oven is now firing any differently than it was. I suspect that JW is more concerned about how long his big oven takes to reach pizza temp and the amount of fuel consumed to cook only a couple of pizzas, both of which can be easily solved with a smaller oven that has less thermal mass. Unfortunately I can't see how you could retro fit a big oven to achieve this.

[dakzaag]

You could certainly try to line the edges of the oven with firebrick and see if that makes a difference. 5-6 brick would probably do the trick and effectively reduce your oven floor diameter by 3-4 inches. Lay them as shiners ie. on edge. I don't think it would make much difference, but the cost is pretty cheap and the worst that happens is you have a few brick left over.

[Toomulla]

Depending on the height of your door you could try laying another layer of brick on the floor

[david s]

Both of those solutions will reduce the volume of the chamber slightly, unfortunately any gain there is more than outweighed by the increase of the thermal mass resulting in more time getting to temperature and a greater increase in fuel consumption. Give either a try but I'd bet that both solutions would worsen the outcome.

While on a similar theme I have heard an old Italian trick of increasing an ovens thermal mass is to throw in a couple of truck axles when firing up. They increase the thermal mass and being steel are highly conductive,radiating their heat back to the oven interior once the fire has died.

[jwnorris]

Hello all. What an amazing group we have here. I built my oven almost 9 years ago and a year or so after finishing it I faded away from this group thinking I didn't need it any more, Boy, is that a bunch of BS. So what have I learned.

Thermal Mass: Some is good, too much is not so good. Didn't occur to me that reducing the interior would increase the mass. This might prove to be counter-productive and take more wood and time.

Curing: Never entered my mind that a few cracks would make such an impact. I have noticed several cracks and have just recently started to patch them.

My WFO is outside, uncovered, but the wood is kept dry. I just continue cooking and patching and will be taking copious notes. I'll report when I know more.

And a big thanks to SableSprings, David S, Dakzaag, & Tomulla for all of your input.

J W

[jwnorris]

As I continue patching another thought/question has popped into my head. Could I add more insulation to the outside of my WFO - using it to give the oven a different shape, say a face or head or something? Would this have a negative impact - on performance, cooking time, firing time, heat holding duration, and whatever I can't think of at this time??

Forever In Your Debt,

J W

[RandyJ]

I don't think you can ever have to much insulation on your oven. Well within reason of course it becomes cost prohibitive after a while. But otherwise it will not cause longer heat up times if anything it will shorten it a little by retaining more of the heat. Where you really see the benefits is with retained heat. It will hold a higher temp for longer after the fire is out. I recently did a beer can chicken 2 days after I put the fire out and still had 631F 8 days after that I was at 134F. I did use a lot of insulation for this reason.

Randy

[SableSprings]

As Randy noted, the extra insulation will give you a little better heating time (still the same mass to heat up) but mostly increased heat retention.

My short, beavertail dome has an outside facade that gives it the appearance of a half-barrel style oven...so yes, once the inner oven is functioning and insulated you can create just about any outside shape you want. I remember seeing an oven in the forum that had an outside vegetable/herb/flower garden planted around its dome...wow, I loved the concept and execution of the idea. Again -as always -, it's the matter of making absolutely sure your insulation will stay dry (or that minor moisture uptake can be easily dried out with a couple of firings...normally involving either cover, waterproofing, or a venting & drainage system...or the absolute love of curing your oven every time you intend to use it ).