crack in top of over

[ross]

Hi All

What an exciting afternoon....

Ive just had my first big fire ( it was a beauty ) in my oven and theres a crack at the very top with whisps of smoke where coming through...see pic
its about 5 ins long

The oven is only small 32 ins so gets hot quick ive not insulated it with a blanket or outer vermiculite yet but did 2 good coats of refrac cement especially above the top centre...

Ive had 4 fires up to date going upto around 200C with one layer of cement on and the outer dome didnt get even get hot, then all of a sudden today with a bigger fire came the crack... even with 2 layers of good refrac cement ( Maybe i didnt give the 2nd layer long enough to harden ).....Im sure that with a fire blanket and vermiculite over top I wouldnt have even noticed the cracks..

The heat of the dome inside at the top when it happend was 300C
and outside is is currently ( where the crack is ) is 80C ...so heat is escaping

the dome keystone etc is all very very tight and well built and not packed between joints with mortar and im more than happy with my dome build..

But Whats best to do now???...

leave it and put another layer of concreate over the top and carry on with the insulation blanket etc

or chip it /grind it away back to the brick below the crack and re-cement the 2 layers...then put my outer insulation over and stop messing around...lol

advice please

[Ken524]

Re: crack in top of over

Ross,

How does it look from the inside? Is it a wide crack or hard to see?

The dome needs to expand and contract, and that's the spot it picked for the movement. I think if you repair it, it will recrack or crack in another spot.

If it doesn't look too bad on the inside, I think I would start insulating and press on. Once it's insulated, you should not lose any heat or smoke out the crack.

[ross]

Re: crack in top of over

Hi Ken

Thanks for the help first of all

Its all a bit black in there and still warm....lol

Ive taken a pic ( see attatched ) and from looking with a torch there are gaps between the bricks right at the top where the mortar has shrunk...not bad ones tho...and no cracks in the bricks

I think I might tmw get some refrac cement and re-point the inside top around the keystone..and aslo grind the outer dome cement at the top and redo that that way i can see where the smoke / air is getting out...and then re fire very gently..i dont think it will harm it!!!!

Ive not got a good pic of the inside top before the first fire but it was all pointed well

I dont mind spending the time to get it right - its been so enjoyable doing it id rather get it right..

What you think???

[Ken524]

Re: crack in top of over

It doesn't look too bad. If you want to re-point, that's fine. It certainly won't hurt anything.

You might then want to put some insulation blankets or verculite-cement over it and start curing again very slowly.

There is some debate over whether curing with or without insulation will result in less cracks.

Good luck!!