Hello All

[mnlewis]

Ok, I am a little confused here. I have been doing the curing after letting the vermiculite mixture cure on its own for two weeks. I have 5 1/2 to 6 inches of the vermiculite portland lime mixture over the oven. I noticed that it still gets very hot on the out side of the oven, is this normal?
My vermiculite/portland mix is 5 to 1, mixed it dry until all the vermiculite was gray with portland.
Did I do something wrong? Is this normal? I read on the threads that it should only get to about 100, I know it is hotter then that. I don't have a thermo to check it but it is hot to the touch. I have 4" on the bottom with 4" block, I filled the block with the vermiculite mix.
I have been doing small fires in it for three days, not very hot just enough to get the bricks nice and warm. Will do that again today then tomorrow, I will put a slightly bigger fire in it then on Wendesday I am going to do a screaming, blazing run it up as high as I can fire...... Call the fire department.

[christo]

My only thought here is moisture.

With all the rain we've had could your insulation layer still be wet?

It would make sense to me with the heat you have on the layer - are you seeing any steam?

If so, you may want a few more drying fires....

[mnlewis]

Thanks Christo, that makes a lot of sense, forgot about that but I thought after three days of drying heat it would have taken care of that.
Will do another but larger fire tomorrow, then Wed will do the massive one.... Saturday will be the first cooking day in it. My other problem is I took a tree that came down in one of the Huricanes and found it to be a Poplar, kind of soft wood. Hunting my property for some oak, if not will have to purchase some.

[CanuckJim]

Put a small space heater inside the oven. Set it on 72F and let it run, day and night, for the time remaining. Call it insurance against cracking.

Jim

[mnlewis]

Ok read this too late, I ran a small fire again yesterday and this morning, put a little bigger fire in it and Oh No, cracked the back, checked the brick, no broken joints or bricks but have to repair the back crack, one brick came loose on the front arch, not a problem there, can fix that easy.

How is best way to fix the crack?

[james]

Sorry about the cracks. Can you seal the oven with refractory mortar from the outside and the outside? I would definitely add a thick enough layer from the outside to seal in any smoke and hot air. My vent cracked on my first Scott oven, and I did all of my repair from the outsidel, using fireclay mortar.

Also, I think it's time to make a permanent posting on oven curing. My guess is that your experience will happen again. We should start recommending that everyone err on the side of caution when curing your oven. I have abused the curing time to see what would happen, but that was on "fast" installations I did that really were not permanent. With all of the energy and time and goes into these great ovens, I think we need to recommend a "go slow" approach.

On the heat, your were driving out moisture, which had turned to steam. In a perfect world, you would drive moisture out of your oven slowly, where you never make steam.

And with all of this, brick ovens just crack. I'm sure that with your repairs, all will be well.

James

[CanuckJim]

James,

I agree that a permanent posting on curing would be an excellent idea. I've answered curing questions so many times I've lost count. My Scott oven is very high mass, and I've experienced no cracking at all, anywhere, but I was extremely careful with curing.

When the dome was finished, I put a space heater inside and let it run for a week at 75 F, exposing the outside to as much sun as possible. The outside was covered with a tent made from a tarp to keep off the rain. When the cladding was poured, 8 or so inches, I put the space heater back in, for two weeks, and did the same routine with the tarp. In the meantime, the four inch block enclosure was built, etc., etc. I had a lot to do, so it was probably three weeks or so before the first VERY small fires were built, one a day, for a week more. The hearth never got above about 200 F.

It's my opinion that refractories set more quickly than ordinary cement, but they cure more slowly.

I've already made some repair suggestions to mnl.

Have a care.

Jim