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-   -   Help! Losing heat like water out of a tap (http://www.fornobravo.com/forum/f2/help-losing-heat-like-water-out-12965.html)

Rodway Plazza 05-17-2010 02:20 PM

Help! Losing heat like water out of a tap
 
Hi All,
Can anyone help, we have just had a WFO built:), we tried it at the weekend and it was very disappointing. We did manage to cook some pizzas but it was very painful. Our dome cracked! We have zero insulation to the dome .What would be the best solution / materials to be used would insulations quilt be the most practical? Covered with render?
The base is on a tradition mix of concert! I have got the room to put another layer of fire bricks on top of the ones that sit on of the concert base. Would this be best? Or say a 35mm insulation board and a 35mm brick or just a 75mm brick? Please help if you can.:confused:

Many Thanks, the Rodway’s

RTflorida 05-17-2010 10:09 PM

Re: Help! Losing heat like water out of a tap
 
Sorry to say, it sucks to be you right now. You have the double whammy of no hearth insulation and no dome insulation. It is not an oven, it is a fireplace.
Here are a few questions and suggestions:
What is the dome constructed of? How thick? what type of finish? As long as it is not a foot thick, you can add a good layer of insulation and have an effective oven - 3+ inches of refractory blanket or 4+ inches of perlite/portland cement or vermiculite/portland cement. Then a water resistant render layer or 2. As for the crack, ALL ovens crack somewhere, it is going to happen and you can't stop it......Hairline cracks that don't really open up can actually be left alone. Any that open up 1/8" of an inch or more are worth trying to patch, although patching cracks is probably only 50%-75% effective. A properly built dome should remain structurally sound with a few cracks.

The lack of insulation under your hearth is the BIG issue. Somehow, you need to get at least 2 inches of insulation board directly under the heath bricks and ABOVE the concrete base/hearth support slab. Is your entry tall enough that you can pull out (maybe have to grind and pry) the hearth bricks, add insulation, and replace the hearth bricks? What kind of entry height would you have in relation to the interior dome height if you did this?
As a last resort if you cannot do the above, do you have access to the underside of the support slab? if so, you could add the insulation directly under the support slab and add a support system to keep it in place. I will warn you, this will leave you with an old school "bread oven" that will require a lot of wood and very big, long firings to heat all of that mass to pizza temps. On the plus side, this would offer alot of heat retention for several bread bakes and plenty of heat for other retained heat cooking. Again, it would require alot of wood and long firings (several hrs), but you could still effectively make good pizza.
I'm sure others have additional thoughts, this topic used to come up quite a bit. Its a shame you did not find the site before your build.
I strongly suggest that you visit the Forno Bravo store and "purchase" the Pompeii oven plans (actually they are FREE, FREE, FREE). The plans will show you exactly how your oven SHOULD have been constructed and should give you more insite as to how you may change things based on what you actually have to work with.
GOOD LUCK and keep us posted.......Pictures would be helpful, add them if you can.

RT

Jed 05-17-2010 10:23 PM

Re: Help! Losing heat like water out of a tap
 
Rodway Plazza,

RT Florida has pretty will summed up your situation.

The physics of an oven require insulation if you want to get an oven to temperature in a short period of time, and with a 'reasonable' amount of wood. - insulation to separate the fire brick / fire box of the oven from everything else - ie - the supporting structure and all sides and top of the oven.

Another point worth mentioning is that if this is your first use of the oven, did you go through a complete 'curing' process? A masonry oven is built using lots of water, that then takes a long time to cure and cook from the masonry. It can take a full week or two of curing fires, and as many as a dozen full on pizza cooking fires to get an oven 'cured' to the point it will work consistently well.

Do download a copy of the Pompeii oven construction plans from this web site, and read - particularly the stuff about insulating. It will help you with some of the details.

And send along some photo's. We might come up with another idea or two to help get this oven of yours working well.

They are a ton of fun, and produce great food, so don't give up on your oven! It might take a little work to get it 'dialed in', but so what... it's only work! And then you will have an excellent oven you can use and enjoy.

Good luck,

JED

Rodway Plazza 05-17-2010 10:59 PM

Re: Help! Losing heat like water out of a tap
 
The thickness of the dome is a fire brick arch and 12mm (ish) of render on top, I do have scope to add installation I think Ceramic fibre blanket would be the best way? Are your thoughts the same how much topping would propose? The height of the entry is around 20’’ and the internal arch around 24’’/26’’, so I guess I could reduce this by an additional layer of fire bricks? Would this help? I can also get to the bottom of the base would it be best to insulated with a ceramic board?

nissanneill 05-18-2010 03:21 AM

Re: Help! Losing heat like water out of a tap
 
Sad to hear of your predicament.
I see the quickest, best and easiest solution is to


KNOCK IT DOWN, SALVAGE THE BRICKS AND REBUILD IT TO THE FB PLANS.

Sorry but that is what I would do, (and you might have to to get it to oerform as it should. Anything else will only be a patch up!

Neill

Eric Pfeifer 05-18-2010 04:14 AM

Re: Help! Losing heat like water out of a tap
 
Agree. You need insulation under and around that thing. Time for a mourning beer and a 4 pound maul and chisel.

egalecki 05-18-2010 05:49 AM

Re: Help! Losing heat like water out of a tap
 
I think your dome is actually taller than the FB plans call for- so is your entryway. This means that you can add insulation under your floor as you have proposed. 2 inches is a good amount of the rigid insulation to use.

You can add the ceramic blanket to the top as well. 2 inches or more would be good. Once that's done, you should see a difference in the heat up time and in the heat retention.

You can either build an enclosure or put render back over your insulation. I have two inches of ceramic blanket over mine with an additional 3-4 inches of vermiculite concrete on top of that, followed by the stucco (what we call render in the US, apparently).

As far as cracks go, as long as the structural integrity isn't compromised, spackle over that baby. All domes crack some, as far as I know, and as long as the crack doesn't translate to the outer shell once you've insulated, it should be fine. If you get cracks in that outer shell, fix them promptly or you'll get water damage.

SCChris 05-18-2010 07:34 AM

Re: Help! Losing heat like water out of a tap
 
The inner arch should be 63% of the internal oven height, if your higher than this 63% you'll lose more heat out the doorway than you want. If your height is greater than the 63% then you have some room to get insulation under the floor bricks. If your way up there and you can add 3 or more inches of floor then I'd think about 2" of rigid insulation board with half thick firebrick on top. In the US this would add 3.25" of height to the floor without removing the existing floor, not to plans, but it might work for you.. The insulating blanket is the easiest material to wrap a dome shape with and get a good tailored fit. If you're not dead set on having an igloo then a oven house gives you more insulation options and has a better chance of keeping the weather out. Please post photos and measurements.

Best to you.

Chris

kebwi 05-18-2010 07:46 AM

Re: Help! Losing heat like water out of a tap
 
Where'd you get your oven design from? We should compile a list of offenders. Following bad advice on a project this large is worth making note of so others don't go the same route. Did you use a book people should be warned off of?

SCChris 05-18-2010 08:46 AM

Re: Help! Losing heat like water out of a tap
 
Dear Rodway family,

As I mentioned earlier, I think you may have the space to bring up the floor and get your insulation. I also want to say, these ovens are very forgiving with regard to design and execution of the design. Whatever happens and you decide to do, I think you can make the oven work for you.

Some pizza ovens are built in the afternoon and used in the evening and then torn down. Some of these extreme builds don't have any insulation at all. I wouldn't expect to be able to braise in these ovens, but they work fine for block party pizza. Some primitive ovens in South America are little more than a pile of rocks that contain the fire and retain the heat.

Show us what you have and let us give you our opinions as to what your options are / might be.

My bet is that things aren't as bad as they might seem.

Chris


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