Oven Curing

[fremen325]

I took a few days off from my firing/curing schedule. My last burn saw a peak temp at the dome of 800F and about 1/3 from the top a steady reading of 450F (1/3 from the top is what I am using as my reference point). Dome still hasnt gone white which I thought it did at 800F. I have some cracks on the outside though I am considering them to be minor. I am still debating whether to grind them out and put some Heat Stop mortar in them before covering with ceramic fiber blanket insulation.

[fremen325]

I have been slowly building fires each evening in my oven. I did a few days with the beads/brickettes and now am on straight wood. Tonight was my biggest fire to-date but am still peaking at ~520F at the top of the dome and in the 3xxF in the middle/top third of the dome with floor temps around 250-260F. The dome definitely has not yet gone white.

[fremen325]

I just finished reading the whole curing thread. To summarize the thread, do the curing fires low and slow and take longer than you think it should. I got my chimney on today but have not installed the ceramic fiber blanket. I did a few days of space heater (it kept turning off due to the thermostat) and a day of work lamp. The air still feels pretty moist but we are also in the middle of our summer with ambient RH at ~ 70% though the past few days have felt like 100%. My firing plan is to use the head beads/charcoal brickettes for the initial heating cycles then switch to wood. When you use the brickettes, do you just put the starter chimney with the lit brickettes in the oven or do you pour them on to the floor?

[ByrJor]

Re: Oven Curing

I am just getting to the curing phase and am a bit unclear on 2 points for the Casa90 mobile oven.

First topic, I believe that it is common to put a layer of 5:1 perlite /portland cement over the 3" of insulation that came with my Casa90. I have read completely finish the oven before curing which for me would be to add the perlite insulation layer and the stucco layers. I have also read that the perlite/cement layer traps the moisture during the currying process. So fire before or after the perlite/cement layer? (I am still open to comments on if the perlite/cement layer is a good idea. I got the perlite/cement recommendation by making a cold call to a wood fire trailer manufacturer.)

Second topic, I got the 300 and 350 for as long as possible for the first two days and don't go over those temps. But do you hold the 400, 450 and 500 also for as long as possible each of those days? Is there a temperature it needs to cool down to before starting the next cycle? And then just go for the cooking temperatures? Not work your way up to the 800F?

Back ground. I currently have the pieces in place and mortared together, the blanket insulation and chimney on. But I need to rework the location of the decorative arch. When removing the arch I knocked a piece of the mortar that is between the insulation board and the vent landing (i guess it wasn't mortared correctly to begin with and i am a bit concerned about the rest of the mortar) so FB is very unexpectedly sending me a bit of mortar to make the repair. I reluctantly plan to wait one week after I get the mortar and make the rework to start the firing. Depending on the external temperature of the insulation during the curing cycle, I am considering doing the whole 300 to 500 over again after I put on the perlite / cement but that is probably just because I don't really know what I am doing and see no harm other than time.

Thanks Chad
BTW, first WFO and first time posting on a forum..... sorry for the nativity I tried my best to read all the different treads looking for these two clarifications.

[david s]

Re: Oven Curing

There are different recipes for eliminating the water (curing) Read the whole of the curing thread to get a better understanding.

[BackhoeSawyer]

Re: Oven Curing

Anyone ever addressed the seemingly big contradiction in the Pompeii 2.0 plans PDF regarding curing and the recommendations at the beginning of this sticky thread? The PDF recommends a 300?F fire maintained 'all throughout Day 1 and as long as possible into the evening', which is WAY more heat than the short newspaper-only fire recommended here.

After reading and following the PDF instructions for Day 1, and burning a very small fire for about 4 hours, I stumbled upon this thread and got pretty concerned I'd overcooked it. I did get two long but hairline cracks along brick edges, but it's not clear if it's a problem. They open a bit while hot (still hairline), and almost disappear when cool.

Did I get an old version of the PDF? Or maybe it should be updated?

Many thanks to all the wonderful advice on this forum; it's really been a great experience building the oven.

- Mark

[v12spirit]

Re: Oven Curing

Day 5 of curing. Could't resist using a propane gas burner on days 2 and 3. The low continuous 4 hour fire it provided was importnt IMHO in the first 2 or 3 days to gently drive moisture out of a newly built, rather wet oven. Day 4 kindling for 3 hours. Day 5 kindling and 1-2 cm thick sticks for three hours.

I was getting a clear feedback right from the oven without a thermometer. Today, I've got a fourth indicator to stop feeding the fire; a little tickling sound from the refractory. Reckon that if I had responded to that sound in time I could have avoided a hairline crack getting a bit wider; the tickling sound was going from around that crack. However. The two cracks I have got so far are of minor importance.

Interesting how the oven was very sensitive to abrupt heat increase while letting you go to the next heat level safely when exposed to the previous heat level for a suffecient while; a couple of hours say. I think as stated, better let the whole oven see every new level of heat for a while to ensure a smooth shift to the next heat level.

[v12spirit]

Re: Oven Curing

Not sure where you live, but an IR thermometer will only set you back $15 and you could probably have in a couple of days: Amazon.com: ir thermometer

Thanks for the link. I live in Syria that lays on the east coast of the mediterranean sea. Should have thought of buying one. But I have been looking for an analog one to install as an aesthetic finishing icon. Haven't found one that reads up to 500 C yet. So I will not let that delay my build. Amazone stuff didn't hold in my region especially recently. Even though Amazone stuff can ship faster to Paris than one from Damascus to my town if ever it could be delivered safely.

[di11on]

Re: Oven Curing

My oven is a steel 67 cm dome indoor one clad with 3-5 cm thick refractory. I have to do the curing withot thermometer. I understand from this thread that there are two major points to keep in mind when curing.
1- slowly drive out moisture without creating steam
2- run a small fire for the first two days for at least 3-4 hours each, I mean not just reach the 200 and 250 F and done.
Having no concept of temperature, I am doing my "blind" curing like this:
I start a small paper only fire and keep it as long as there is no steam emitted away from the refractory. Once the steam appears I let the fire die down and let the oven equalize. Once the oven cools down to fairly warm I repeat the process trying to increase the fire a little bit. Looks like this approach will take ages to fully cure the oven, but I will be sticking to it at least for 4 days just to stay at the safe side.
My alternative indicators to thermometer that will alarm me not to keep the fire going are any of these:
1- steam emitted from the refractory
2- a clear smell of moist concrete in the kitchen (smells like summer rain on a concrete slab)
3- a little sizzling sound close to the refractory maybe because of the steel shield. I could hear it with my ear an inch close to the cladding.
I will be stopping feeding the fire once any of these happens. Have been following this for the second day now. Cracking only happening at the desired "cracking control" joints except for two of the 15 refractory blocks having hairline cracks so far.

Not sure where you live, but an IR thermometer will only set you back $15 and you could probably have in a couple of days: http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=ir+thermometer

[v12spirit]

Re: Oven Curing

My oven is a steel 67 cm dome indoor one clad with 3-5 cm thick refractory. I have to do the curing withot thermometer. I understand from this thread that there are two major points to keep in mind when curing.
1- slowly drive out moisture without creating steam
2- run a small fire for the first two days for at least 3-4 hours each, I mean not just reach the 200 and 250 F and done.
Having no concept of temperature, I am doing my "blind" curing like this:
I start a small paper only fire and keep it as long as there is no steam emitted away from the refractory. Once the steam appears I let the fire die down and let the oven equalize. Once the oven cools down to fairly warm I repeat the process trying to increase the fire a little bit. Looks like this approach will take ages to fully cure the oven, but I will be sticking to it at least for 4 days just to stay at the safe side.
My alternative indicators to thermometer that will alarm me not to keep the fire going are any of these:
1- steam emitted from the refractory
2- a clear smell of moist concrete in the kitchen (smells like summer rain on a concrete slab)
3- a little sizzling sound close to the refractory maybe because of the steel shield. I could hear it with my ear an inch close to the cladding.
I will be stopping feeding the fire once any of these happens. Have been following this for the second day now. Cracking only happening at the desired "cracking control" joints except for two of the 15 refractory blocks having hairline cracks so far.

[david s]

Re: Oven Curing

Hi all,

Quick question... having waited patiently for 4 weeks, I'm following the 7-fire plan. I've just finished fire 3.

Using my infra-red point and shoot thermometer, I get different temperature readings all over the oven. For example, on today's fire I clocked the apex of the dome at around 220 C, the chimney gas at 120 degrees C and then anything from 80 C up depending where on the dome I was pointing (low and to the side being the lowest).

So... which temperature do I go by?

IR thermometers can be rather misleading in that they read the surface temperature. 10 mm below the surface will give you a lower temp, particularly when you are driving out the water. This big difference in temperature leads to a big difference in expansion rates which can cause damage either microscopically or as visible cracking. Just take it slower than you think is prudent and you should be ok. Also try reading the whole curing thread to get more of an idea what's going on.

[david s]

Re: Oven Curing

I didn't read all of threads, but I get the gist of it for curing.... My question is, I can't be there every day to light up and cure the oven. Can I cure for two days, wait three, start curing for one day wait three and then finish curing the next two.... Is there a problem if there is a gap between days to cure? Thank you. Ray

No problem waiting longer in between fires. In fact there may be an advantage because it gives the moisture present, time to migrate back to the drier parts which then allows you to heat the oven more evenly without having such a huge difference in temperature and hence differing expansion rates.

[That's Amore]

Re: Oven Curing

FYI
don't get to hung up on this process. The temp will and should be highest at the top. Think of the fire brick that is 4" thick needs a long time of steady heat to allow for the brick to obsorb the heat. For a new build it is good to make small fires at first to slowly cure the morter but I found that just adding a pc of wood every so often to maintain a long fire that is low temp to penetrate the brick. This will get out the moisture. then each day do hte same thing but get the temp a little hiher each time.

[di11on]

Re: Oven Curing

Hi all,

Quick question... having waited patiently for 4 weeks, I'm following the 7-fire plan. I've just finished fire 3.

Using my infra-red point and shoot thermometer, I get different temperature readings all over the oven. For example, on today's fire I clocked the apex of the dome at around 220 C, the chimney gas at 120 degrees C and then anything from 80 C up depending where on the dome I was pointing (low and to the side being the lowest).

So... which temperature do I go by?

[checker1965]

Re: Oven Curing

I didn't read all of threads, but I get the gist of it for curing.... My question is, I can't be there every day to light up and cure the oven. Can I cure for two days, wait three, start curing for one day wait three and then finish curing the next two.... Is there a problem if there is a gap between days to cure? Thank you. Ray