Oven Curing

[james]

Re: Oven Curing

Hi Irv,

We switched the curing instructions after your oven went out. It isn't earth shattering, but we think the new instructions are better.

The general idea is the hold the first fire to 300?F all day, close the door and let the oven rest over night, and then hold the second fire at 350?F all day. However you cure your oven, the key is to never let those first fires get too big -- no matter how tempting it can be.

Here is the PDF for the state-of-the-art curing method.
James

[Irv Mac Dowell]

Re: Oven Curing

That is to say, the 300 degree on the first day with a gradual cooldown?

Thanks for the reply.

Irv

[gjbingham]

Re: Oven Curing

The latter, the one you mentioned, is the current prescribed method.

[Irv Mac Dowell]

Re: Oven Curing

My Casa 90 is now complete. I built it as an igloo, with 3 inches of blanket and an additional Perlcrete layer over chicken wire. The oven was finished with two layers of colored stucco.


The instructions for curing that are contained in the instructions that accompanied the oven have a completely different curing schedule from the one James outlined at the beginning of this thread. Those instructions require a 300 degree fire on the first day, the temperature to be maintained all day. The temperature is increased in 100 degree increments over the next four days.

Which scehdule should I follow?

Thanks.

Irvc

[james]

Re: Oven Curing

Hi Stuart,
Let me make sure I have right right. Your Artigiano oven is set on the insulating hearth, and has the insulating blanket around it, but it is not enclosed yet. Is that right?

If that is where you stand, you can start the curing process -- pizza around the corner, and roast chicken even before that!

As always, go slow.
James

[Les]

Re: Oven Curing

Firepie,

Did you use the blanket in addition to the 6 inches of vermiculite/cement?

Les...

[stuart]

Re: Oven Curing

James,

In the initial post you included even the Artigiano in the need for gradual curing fires. Is this because of the oven itself or the masonry built around it? Currently my Artigiano sits on a completed hearth stand waiting for the Concrete Countertop contractor (me) to get his act together and build the oven landing/hearth. The Artigiano sat in my garage for months waiting for the rains in Texas to stop and now it has been sitting in the heat for few weeks.

My family is drooling at the thought of pizzas from the Artigiano and I'm curious what curing fires must be done for my oven in this state? Do I need to proceed with the weeks worth of fires if my oven is unenclosed and sitting on the stand? Later on, what about once it has been enclosed in a steel stud doghouse type enclosure?

[Hendo]

Re: Oven Curing

A while back, I found my refractory mortar manufacturer's recommendations for "initial heat-up". I assume this refers to the procedure of heat curing the oven prior to using the first time, rather than for each use(!). I posted it on this thread at http://www.fornobravo.com/forum/16/o....html#post8498. The graph shows a gentle ramp at 50?C (90?F) per hour to 200?C (392?F) and holding at this temperature for ? hour per inch of lining thickness. After this, the recommendation is to ramp at no greater than 200?C (360?F) per hour up to operating temperature.

How one would do this with a small wood fire is not immediately obvious to me, but it does run counter to the cycling approach mentioned here. I wonder if the cycling method was introduced to take into account the (9-5) work commitments of most builders, or is there another reason for it?

Paul.

[RTflorida]

Re: Oven Curing

I can only speak from my experience and my interpretation of the instructions and the many posts I've read.

My first fire (if you want to call it that) was to 200 degrees. With an outside air temp of around 90 degrees and the surface temps about the same inside the oven......it really only took 3 or 4 wads of newspaper to reach 200 and only lasted seconds. As I understood the instructions - just reach that temp and let it burn out, don't maintain it for hours. The cool down from 200 to 90 only took 2-3 hrs. I then proceeded to do the same for 300 degrees...letting it cool down overnight.
Day 2, I went to 400 - just reaching a surface temp inside the dome, no saturation. I believe this was at 7 or 8 am on a Sunday, at 10 or 11 pm the bricks had cooled to the outside air temp so I proceeded to 500...this being the first actual real fire - using quite a few 1" - 1 1/2" sticks, probably lasted 10-15 minutes. let it burn out, shoveled out the small coals and ashes.
Actually had to let it sit until Tues evening before attempting 600 degrees (was out of town for work on Monday).....I have no more spare time than anyone else - the main reason I was building a fire at 11 pm on a Sunday.

In any case...I followed the instructions and allowed for complete cooling before each hotter fire. Even though I double up on 2 days it still took me a full week to cure...for some reason my company expects me to work if I want to get paid (helps pay for these projects).

Nick...as long as you go through a complete heat and cool cycle for each fire, there shouldn't be any issues. If I am not mistaken, it has been a few weeks since you actually completed your dome, so its had a good bit of time to cure naturally.....you just need the heat cycles now.
Good Luck
RT

[redbricknick]

Re: Oven Curing

Thanks fellas.. I'm going to go for it with a second 300 degree fire now.. Noon, and burn a four hundred degree one at Ten tonight.. I have faith.

[CanuckJim]

Re: Oven Curing

JE,

Curing is an exothermic reaction. So far as I understand it, the heat and cooling cycling allows the material to expand and contract as it cures, thus strengthening the final, cured product. Refractories can be brittle unless you allow for this, leading to cracking, I think.

Incomplete, but the best I can do. You gotta envy those with copious amounts of free time.

Jim

[jengineer]

Re: Oven Curing

Jim - I am playing the role of Rednick here. But I really want to go fast and I need to have a real burn this Sunday.

What is the mechanism needs or chemistry or action that is occurring during the cool down the necessitates the cycling action of applied heat and then a rest and slow cool down.

I think we are at the point of just because you said so isn't going to satisfy the why. I understand the wait 28 days for a cure after all I have been to Boulder dam and dad is an engineering geologist in thin arch and earthen dams so i get the cure time. At a loss as to what is going on during applied heat.

[CanuckJim]

Re: Oven Curing

Nick, JE, RT,

I always advise caution and time with curing fires. However, if the oven is allowed to REALLY cool down between fires, it should be okay. You're gonna need about ten hours between them, I think. Refractory mortars do have a different composition, but so far as I know the 28 day rule for a full cure and full strength still applies.

Jim

[jengineer]

Re: Oven Curing

Ah someone with copious free time on their hands. What you are talking about is heat soaking the oven to cure it. In the instruction James says to light a series of fires once a day where the oven is brought up to a increasingly higher temperatures. The idea is of a working mans 9-5. he comes home and lights a fire. What a bout the freelancer who has time to kill and a burning desire to get on with with it. Why not make it more like a kiln? Slowly bring the heat up and never relent until you are done?

Question for our Brickmen - does this driving out the heat relentlessly decrease the strength of the bond? i.e. most concrete needs a 28 to 30 day set before it has achieved a large portion of its final strength. The mixes that FB sells and Heat stop are of different chemical properties and probably have different curing needs.

Do we really need to let the oven cool down if the purpose of the fires is to drive off moisture?

[RTflorida]

Re: Oven Curing

I did 2 fires a day for the first 3 days...one in the morning and again in the evening. No problems with mine.