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Rickaroonie 05-24-2013 06:45 PM

Firing oven, when?
 
Should be finished in a week or so with the fire bricks, but is it better to start firing without the insulation and finish cement or after?

Just wondering what FB people have done.

Rickaroonie

Les 05-24-2013 07:17 PM

Re: Firing oven, when?
 
I didn't do a cure but it would be better to drive out the moisture before you insulate and finish.

SCChris 05-24-2013 07:25 PM

Re: Firing oven, when?
 
My opinion is that a constant heat source over a long time has the best effect on curing. Early on, I used a 500w quartz work lamp to heat the interior and this heat will warm the whole structure and the convection will dry the structure. I used a temporary door slightly gapped to allow heating and a bit of air movement, and kept this up for 4 or 5 days.. The exterior was then wrapped, loosely, with insulation and I kept the fire low and slow in an effort to saturate the structure with heat very slowly and over very long burns. My goal was to minimize the differences of heat in the structure, to get the water moving and keep it moving.. The curing thread is a really good source with lots of thoughtful input..

Chris

http://www.fornobravo.com/forum/f16/...ing-17586.html

woodboiler 05-24-2013 08:36 PM

Re: Firing oven, when?
 
Most mortar and cement mixes take 28 days to cure. It's better to keep the humidity up during this time.

I kept mine covered and damp in plastic during the building and about 3 weeks after I placed the last brick on the dome.
Let it air dry for a week.
Placed a quartz lamp in it for a week with a temp door.

I did a bunch of tinny fires over 8 days slowly bring the temp up to 700* before I added the blanket isolation.
I've been using the oven twice a week and have not decided on how I want to finish mine.
I wanted to be able to pull the isolation off after a few weeks to check for cracks before I fished mine.

http://www.fornobravo.com/forum/f6/i...ons-19394.html

Rickaroonie 05-24-2013 08:55 PM

Re: Firing oven, when?
 
Wow, thanks guys for getting back so promptly. Much appreciated. That helps alot. I'll start with the lamp and move on to low fires before the insulation.

Will check out the info on fireing off.
Rickaroonie

fabby 05-25-2013 05:39 PM

Re: Firing oven, when?
 
1 Attachment(s)
I'm a neophyte, but, Les, brickie in oz , tscaborugh(sp?) and others will steer you right. I was slow and waited to build my outer archs and chimney before I started firings.
As a result, I think my dome was curing about a month before any fire. That worked out really well. I started with really small and limited fires, following James at FB's instuctions. By the fourth fire, maybe up to 4-450F. My dome began to clear on the seventh fire, and then I added the blanket and started the stucco for the dome. Let it set a week before firing again. Not intentionally, just the way my schedule and weather allowed.

Attachment 35959

Tscarborough 05-25-2013 05:51 PM

Re: Firing oven, when?
 
If you are using refractory cement (calcium aluminate cement) then you do not need to wait 28 days or keep it moist for cure. It relies on a different chemical reaction than a portland cement based "refractory cement". Even with the PC mix, you do not need to wait or keep it moist, as the PC is only there to gauge (provide a rapid set) the material.

Mix it (homebrew) to the optimal degree of wetness to allow you to lay the bricks, and try not to add more water to the oven than you have to during construction.

david s 05-25-2013 06:28 PM

Re: Firing oven, when?
 
There are two schools of thought re driving out the water before or after insulation. If you do the water elimination before insulating you can inspect the outer surface of your bricks and check the integrity of the mortar joins (cracks). It also allows moisture to escape to the atmosphere more easily rather than being held back in the insulation layer. The downside is that there will be a greater difference in the outer surface temperature of the dome walls to that of the inner surface and this leads to uneven expansion rates and stresses that can cause cracking. I prefer to eliminate the water (I prefer this term rather than "curing" otherwise it can be confused with curing of cement which is holding in the moisture rather than reducing it) after insulating as it helps even out the temperature more. But I think either is Ok so long as you take it slowly( and that usually means slower and longer than you think.
Driving out the water before doing the outside shell is also preferable, otherwise you risk building up pressure in the insulation layer which can crack the outside shell.

An example of the temperature difference problem creating cracking is that of an uninsulated clay flue liner which is prone to cracking. If it is insulated on the outside it does not crack.

woodboiler 05-25-2013 07:55 PM

Re: Firing oven, when?
 
Quote:

Originally Posted by Tscarborough (Post 153676)
If you are using refractory cement (calcium aluminate cement) then you do not need to wait 28 days or keep it moist for cure. It relies on a different chemical reaction than a portland cement based "refractory cement". Even with the PC mix, you do not need to wait or keep it moist, as the PC is only there to gauge (provide a rapid set) the material.

Mix it (homebrew) to the optimal degree of wetness to allow you to lay the bricks, and try not to add more water to the oven than you have to during construction.

Thanks that sent me off to the net for a lot of reading and learning.


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