Too hot too fast. Strong concrete smell.

[Hattori-Hanzo]

Hey all.

Currently part way through my cast oven build, the dome is cast, the ceramic blanket and outer Vcrete layer is done.

Due to the weather and time/work my oven has been air curing at this stage for the last 5 weeks, under a tarp and in fresh air when the weather has been good.

Tonight I finally had a chance to light the oven. I've read the oven curing thread and tried to adhere to the advise of low and slow over the course of 5 days but unfortunately my first fire got too hot.

I'd just added a few more pieces of oak to the fire when I heard a loud pop and bang and something flew out of the oven and hit me.
At first I thought it was just the wood popping and cracking as it does but as I looked down I could see small pieces of the dome laying on the floor.

I quickly spread the wood out in an attempt to reduce the heat which seemed to work and left the fire to burn out.

Looking into the oven I can see chunks of the dome have been blown out. I'm guessing that trapped moisture has turned to steam and blown the pieces out?
I thought the dome would have been dryer than it appears to be and the fire while going strong wasn't a blazing inferno so warning to all others that are coming up to this stage.

Fortunately the chunks that have come out are only thin, maybe 3-5mm at the most and I can't see any cracks in the dome.

Couple of pictures of the damage

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Have I been lucky and can I just leave these or do I need to try and fill/repair them in some way and if so how?

My second question is regarding a strong cement smell coming from the oven.
Any one who has done a home brew dome did you experience the same thing and if so how long did it last?
I followed the 3.1.1.1 ratio for the home brew as best as I could.

It's an unpleasant smell that's given me a bit of a headache and I wouldn't like to cook food with it still present.

thanks for any help with the matters.

[david s]

Normally 7 fires in 7 days getting progressively bigger. The early fires should be long and low avoiding any flame impingement on the dome. A combination of wood and brickettes are a good way to avoid this. Sounds like you had it covered too much and the sun/wind didn’t have much of a chance to dry it. Repairing cracks and thin spalls is rarely successful and requires resetting the area. If it were mine I wouldn’t attempt it. Try the plastic over the vermicrete insulation during firing to see if any moisture condenses under it. Also if you see visible steam you’re going at it too hard, back off. Did you add the polypropylene burnout fibres to the homebrew? Because you don't have your own build thread I couldn't check your progress.

[Hattori-Hanzo]

Thanks for the reply David.
The weather hasn't been great so that hasn't helped.
Like you say I just let the fire get to large, it's surprising how quickly it gets going with the addition of just a few thin pieces of wood. The fire was only going for 10-15 minutes.

I did add the fibres, could this maybe what I'm smelling?

[david s]

That's a possiblity.It also could be the lime.

[Mullster]

Hattori-Hanzo gutted for you. I hope with some time to dry out and some smaller fires you’ll recover it. Got my fingers crossed

[hughjamton]

Hi Hattori-Hanzo, did the concrete smell go in the end?

[Hattori-Hanzo]

Two and a half weeks on and the smell is still there, though not as strong as it was but still unpleasant.

Hoping with a few more fires it will eventually go.

[hughjamton]

Did you find out if anyone else suffered with the same problem?

[Hattori-Hanzo]

There are a few cast builds going on at the moment and no one else has come forward with the same issue so it may just be me.
It could be due to my mixing ratios or the brand of cement/lime I used.
Either way I hope the smell goes as I don't fancy cooking in the oven if it persists.

[hughjamton]

There are a few cast builds going on at the moment and no one else has come forward with the same issue so it may just be me.
It could be due to my mixing ratios or the brand of cement/lime I used.
Either way I hope the smell goes as I don't fancy cooking in the oven if it persists.

I'm probably starting my fires this weekend, I'll let you know how I get on.

[Mullster]

I'm probably starting my fires this weekend, I'll let you know how I get on.

Me too - so I’ll watch out for the same

[Mullster]

Hattori-Hanzo how is the oven?

[hughjamton]

I've had 5 curing fires so far and I have no concrete smells.
Did you use ordinary Portland cement in your mix?

[Hattori-Hanzo]

I used the standard blue circle portland cement and Hanson hydrated lime.

The initial smell could have been caused by my first curing fire being to fierce driving out moisture rapidly which gave off a strong smell. Had I done smaller fires maybe the smell wouldn't have been so strong.

The initial cement smell has subsided but I can still smell it a bit. I'm yet to fully heat the oven though.