Nathan's 36" SoCal WFO build

[n8huntsman]

Starting the entry arch

I lost a couple weeks due to being out of town for work but I’m back at it. I should finish up the last of the brick work this weekend. I got the chimney parts on order from Canada. Two 45’s, an 8″ and a 36″ section, base plate, bracket, and cap. Came to almost $1000 with shipping! Surprisingly that was cheaper than it would have been in the US due to our current exchange rate. Then it will be time to cure, insulate, and stucco. I can almost smell the pizza!

Couple questions:
Do most of you clean the inside with sulfuric (muriatic) acid to make things pretty?

Do I need to worry about curing the vent arch even though it wont be as hot because of the thermal break? If not, I can start curing now while I finish the arch. The dome has been sitting in the California heat for over a month already.

[rodeair]

Re: Nathan's 36" SoCal WFO build

n8 .. first class job you have going on there. As far as the chimney stuff, as far as I know, U.S. codes don't allow 45 degree bends, thus Canada. I'm in the same boat with trying to figure out the exhaust system. If you can figure out how to shy away from large bends, it would be better. If not there is always the option of an electric blower to help flow if it becomes necessary. The blower would be mounted at the top if I have it figured right. Good luck, nice work!!

[Greenman]

Re: Nathan's 36" SoCal WFO build

If push came to shove it could be helped by an injection of air directed upwards at some point in the chimney. It would be simpler than in line fans etc.

[DavidApp]

Re: Nathan's 36" SoCal WFO build

Looking good.
Take the first fires very slow. These ovens seem to draw very well and the fire can get big and bad very easily. Don't ask how I know.

I did use Muriatic acid to clean up the vent area brickwork but I would think that the fumes would be too much for you to get inside the dome and clean it the same way. My vent area brickwork had some mortar residue that would not wipe off. I had let it get too dry before I wiped. The fumes were pretty bad.

David

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

Im a little confused about curing. I've read two different things. One said to get it up to the temp and keep it there for at least six hours, let it come down and move to the next temp, again holding it for six hours.
The other said to just bring it up to the temp, and let it cool back down, then move on to the next temp.
How long did you guys maintain each temp in the process?

[david s]

Re: Nathan's 36" SoCal WFO build

Curing is a dumb term to use IMO because it gets confused with holding in moisture to enhance the strength of concrete or mortar. When you begin to slowly raise the temperature using fire all you are doing is driving out the water which is exactly the opposite. This needs to be done slowly or steam spalling will result. I don't think it really matters that much if it is done continuously or ramped up and down. You need to do it carefully because the top will dry first and it's temperature will be way hotter than the bottom. This leads to uneven expansion which is stressfull to your refractory materials. Allowing the oven to cool brings the temperature of all of the oven back to the same temperature. If left longer some of the water will also migrate back to the dryer parts of the oven so you can then start increasing the temperature again. If you see steam you are going at it too fast, back off. For the temperatures we fire to there are not really any chemical changes taking place in the refractory we are really only removing mechanical water.

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

I was at 300?F last night for 6 hours and saw zero steam. I then took it to 350 today again with no steam. But I did see a hairline crack open up in the mortar joint but no smoke escaping. The piece of 2x4 was dying down so I tossed another in and as others have done, spiked the temp to 550. I let that die down and haven't seen any ill effects and still zero steam. The dome did sit for 38 days in the California sun. Tomorrow I think I'll take it to 450 and immediately back down to get back on track unless someone thinks I can skip that since I accidently cleared that step today. I don't have insulation on so the outside is only measuring 170 with the infrared, even while the inside was 550. Is that indicative of anything?

[DavidApp]

Re: Nathan's 36" SoCal WFO build

Hello Nathan

Someone suggested to me that I put a sheet of plastic over the oven to see if there is any moisture being driven off. The steam will condense on the plastic. It was cold here when I was doing my first fires so I am not sure if the plastic trick would work when it is warmer. It may be that it collects the small amounts of steam that is invisible and concentrates it.

I did notice a big variation in the dome temperature top to bottom at first. Seems that the lower parts may be wetter because as you build water gets splashed on the lower sections and water does run down hill.
So check the temp. Dome, mid dome and just above the soldier level looking for the temperatures to be similar. Things seemed to even out after I had my door to keep the heat in the oven.

David

[n8huntsman]

Finally got around to finishing the entry arch and chimney last week.

[n8huntsman]

First fire!

First fire! Seems to be drawing just fine, even without the chimney attached. Very little smoke out the front. The last photo shows the chimney attached with the 45° elbows.

[n8huntsman]

Cracks!

Somewhere around 350?F the cracks started to open up. I haven’t seen any smoke come from any of them. Should I grind these out and re-mortar, or will they just come back? I assume these are normal expansion cracks and nothing to worry about?
Also, last night when I first fired it up and was getting a lot of smoke through the chimney, the stainless thermal break face got pretty hot and broke free from the mortar as the metal started to curl a bit. It was a pretty loud pop, scared me a bit till I figured out what it was. You can see the separation in the photo. Once it cooled off it came right back but I’m going to have to come up with something to prevent that or I’ll never get a good seal there.

[n8huntsman]

It’s all finally starting to come together.

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

Any thoughts on those cracks? Going to be time to insulate it shortly.

[DavidApp]

Re: Nathan's 36" SoCal WFO build

Hello Nathan

I am not sure but I imagine most ovens have some cracks if you take a close look. Uneven heating causing expansion that has to go somewhere. Very unlikely to cause structural failure. Just a bit disappointing after all the hard work.

I had a coat of mortar and one layer of insulation on before I started my firing so I do not know if I have similar cracks in the dome. I do have a crack in the inner arch that has opened up to about 1/16" and stayed there. I can not see any evidence of cracks on the inside of the dome.

David

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

Ok. Sounds like I'll be good to go on the insulation then. I'm not really disappointed. I kinda expected it from what I read. Just wasn't sure if I should fill them or not. My gut tells me there is no need.