Measuring curing temp

[Dave T]

I'm on the 5th day of curing, so it's starting to get pretty hot in there. I've read through the curing instructions on this forum, but am not clear as to where I'm supposed to be measuring the temperature. I know it's not an exact science, but I'm using an IR thermometer and am getting wildly different temp readings. Where should I be measuring the temperature? On the ceiling over the fire? The sides? The floor? For example, I'm seeing 650 degrees over the fire, but only around 200 degrees on the floor in the corner.

[david s]

Yes, that is because of the moisture present. The water in the refractory will hold the temperature down in that place. Temperature difference leads to expansion difference which in turn leads to stress and possible cracking. Allowing the oven to cool returns the temperatures to even out so you can start again. It also allows moisture to remigrate somewhat, back to the parts you've already dried. Try not to let flames impinge directly on the dome and spread the fire out to the perimeter where the oven is colder. Take you're time. Remember that an IR only reads the surface temp, an inch below the surface would tell another story. Reading about half way up the dome gives a more average reading.

[Dave T]

Ok, I'll spread the fire out and measure halfway up the dome. Hopefully it will be more consistent when I spread the fire out. I wouldn't think the cooler areas are cool because of moisture - they're thick fire bricks. My theory was that the cool areas were further from the fire. But we'll see how it looks after I spread it out. The reason I haven't been spreading it out is because I have very wet wood and have been putting logs off to the side to dry out.

[Wozza]

I cured mine a few weeks back and kept some figures. With the exception of one small crack, I had no problems. My build is here: http://www.fornobravo.com/community/...mpeii-in-bondi

The air temps below were taken with a cheap oven thermometer (fire at one side and the thermometer about where you’d have your pizza)and the walls, dome and floor with an IR gun. There were 6 curing fires all told and the hours listed were the actual time that I had each burning. The temps were the maximum achieved. When each was done, I blocked the entrance with some Hebel blocks and let the oven soak in the heat for (generally) 24 hours. Temps are in Centigrade.

[Dave T]

Thanks Wozza! I don't think in centigrade, so I'm not sure how your temps compare to mine. Why didn't you measure the floor until the last day? Under your dome temp - was that the top of the dome or the side? I'd ignore the readings on the oven thermometer - those things are useless. What is the units for time? Hours I guess? That's a lot longer than I was planning on burning my fires.

I'm having a hard time david s's insturctions above. I can't really avoid having the fire hit the dome. I need to stack the fire up somewhat to let air under the wood, and at that height, it hits the dome when it gets going. Today was my 700 degree (F) day. I got the fire going and then knocked it down and spread it out as per david's instructions. But then I just had a spread of smoldering coals and wood, and the temp started dropping. So then I added some more wood to get the fire going again. The flames were hitting the ceiling, and the top of the dome turned white. The top of the dome read over 1000 degrees, but the coolest parts of the oven - the wall and sides in the corners, were around 400 degrees.

So I'm still unable to get a consistent temp throughout the oven, but I guess I won't sweat about it. I did see one small crack in the dome, it doesn't look like a big deal. Maybe 4 inches long, about the thickness of a piece of paper. I wouldn't have been able to see it if the dome hadn't turned white.

[Wozza]

I was more concerned with the top and sides of the dome than the floor, so I didn’t check the floor until I thought I was nearly at pizza temps.

All my fires were built on top of a small griddle I had lying around. I supported that off the floor with a couple of bits of Hebel block and that helped air circulation so I didn’t have to build the fire too high. But yeah, you’ll still get those flames licking across the top at some point. Especially on the fifth and sixth fires.

I’ve no idea how accurate the cheap and cheerful thermometers are but at least they’ll tell you that today’s fire is hotter then yesterdays. I’m not sure that it’s really that important that the temp is measuring 200 if it’s actually 220. But if you did 200 yesterday and it goes of the scale on the next one (mine goes up to 350 degrees C), then whoa…maybe too much too soon.

My first three fires (at 9 hours each) were done on a long weekend when I had other work to do in the garden, so I could keep checking it every so often and I think that was a benefit. It seems to me that if you can keep the earlier fires going as long as possible, then the (relatively) low heat can soak into the bricks and gradually ease out the moisture. That makes the next few fires less of a thermal shock to the oven. But even then I made sure it was a very gradual increase in heat for each individual fire. So for example, the fifth fire at 300 degrees, I wouldn’t have reached that temp until close to the 3 hour mark.

And I seem to notice that the urge to throw that one extra piece of wood on ‘just to crank it up a touch’ seemed to increase depending on the number of beers consumed. I must say, it’s quite a pleasant way to spend an evening. The fact that you can cook pizzas in these things seems almost a bonus.

You seem to have cleared the dome earlier than expected. Mine didn’t clear until the end of the sixth fire, but if you’ve just got the one small crack, then it seems to be going OK. The crack I got was about the same size and I didn’t see it until after the 6^th fire when the dome cleared. Got a littler paranoid and crawled inside when it was cool and managed to get some high temp mortar rubbed into it. Not sure that it did any good but hell, was I black when I crawled back out. Took a lot of scrubbing to get that soot off…...

Incidentally, the link I put in to my build doersn't seem to work. But if you need to check out some more details on my curing, then go the Regional Forums - Australia and mine is the 'New 36" Pompeii in Bondi'.

[Gulf]

Wozza,
Take the .\ off and the end of the link and it will work .

[Wozza]

Wozza,
Take the .\ off and the end of the link and it will work .

Cheers, Gulf. That worked OK...

[Dave T]

I didn't know you should have your curing fires run so long. The sticky thread here says to let the fire go out as soon as you reach temp. But I just read further into that thread, and now see that the current recommendation is to run the cueing fires all day. That's on something like the 6th page of the thread. Aargh! They should update the initial post with the correct instructions.

[david s]

If the top of the oven interior has cleared, but the bottom of the dome has a persistent ring of black unburnt carbon around it this is an indication that the bottom is still wet. Your IR should tell you that it is way cooler than the top of the oven. This is exactly the point at which damage can occur because it means a huge difference in expansion and when you probably get really keen to push the temp up to get it all white. The dryer top of the oven starts to heat up even more rapidly while the lower parts are held cooler because of the moisture present. Using brickettes, charcoal or what we call in Australia heat beads, is a great way to avoid too much flame impingement on the dome. You can use wood as well, but the charcoal is a great way to build up slower burning coals. The air temp thermometers are pretty good I find and actually more useful than an IR gun which reads surface temp. If baking or roasting the cheap air temp thermometers placed right inside the oven do a great and accurate job.

[Dave T]

Ok, thanks. I still wouldn't depend too much on those coil-based thermometers though. I have one in my smoker, and it normally differs by 100 degrees F or more with the thermocouple thermometer I use and trust.

[david s]

Yes they read the temperature by different methods. Also if the air temp thermometer is placed on the floor of the oven while the door is off it is getting cool air flowing over it as it's reading the air temperature. It would show a higher temp with the door in place. Thermocouples read the voltage which is directly related to the temp.