Underfloor heatloss with ceramic fibre board - what temps do you register?

[gaucho1]

Hi all,

Been curing my oven over the last few days and today I've had a medium fire burning all day long as I need to cure the ceramic fibre mastic I used to insulate my dome. (I used 4 layes of 128kg3 25mm CF blanket and then finished with 25kgs of ceramic fibre mastic). For those who haven't used it, the mastic is like plaster but is made from ceramic fibre. We used rigidizer on the blanket then slapped on all the mastic with a troul and keyed it to form a scratch coat. With the heat from the all day fire today it has now hardened and is pretty much ready for the final layer of stucco. With an internal temp of 450 degrees the outside is registering about 50, so I think my dome is well insulated! However the underside of the oven, sticking my hand under the hearth, is quite hot, registering about 160 degrees. I'm a little bit concered that so much heat is being sucked out of the floor, not just for the efficiency of the oven but also for the ability to use that area for wood storage, I guess if I have a very hot oven I could run the risk of starting a fire under there? I used the standard 2" of CF board (or isol board as you guys across the pond call it). So my question for you all is what temps you register from the underside of your hearth, is 160 degrees alarmingly high? Thanks for the input.

gaucho

[Faith In Virginia]

Re: Underfloor heatloss with ceramic fibre board - what temps do you register?

I used 3-1/2 inches of the vermiculite mix. So the heat went through 7"thermal mass 3-1/2 vermiculite and 6' of concrete and after a long hot firing I was warm to the touch. Next time I'll take the temp and let you know.

[lwood]

Re: Underfloor heatloss with ceramic fibre board - what temps do you register?

Keep watching it Gaucho, it may be steam coming out.

[dmun]

Re: Underfloor heatloss with ceramic fibre board - what temps do you register?

Two inches of refractory board is fine under your floor. My guess? Everything's still sopping wet. You'll get better and better results with your first dozen fires as that water is driven out. You may want to hold off on your final layer of stucco until it dries out completely.

[gaucho1]

Re: Underfloor heatloss with ceramic fibre board - what temps do you register?

Thanks for the response guys. It seems that it is giving off much less steam than it was yesterday and the temperatures have dropped. It's probaby just the moisture escaping, the temps underneath now register about 140 degrees - 20 less than yesterday.

It's funny how having invested an incalcubale amount of energy in your oven, the thought that you may have done something wrong makes your feel horror-struck, and then when you realise that it's OK it is a great relief. I know how many hundreds of hours have gone into building it roughly, but I dread to think the number of hours of mental planning, worry, excitement, etc etc. I've even woken in the night dreaming about my oven design or some small overlooked detail which must be rectified and switched the light on to jot it down (much to the distain of my poor sleeping girlfriend!) I'm not sure what I'll actually do when it's finished, building has been such an endeavour, it's become a part of my life - I don't think I ever envisaged actuall finishing it! I guess my next project will have to be mastering my pizza cooking skills. Thanks again guys.

[lwood]

Re: Underfloor heatloss with ceramic fibre board - what temps do you register?

LOL...... Gaucho, I know the feeling. The oven will continue to reveal itself to you. It's really amazing how well they work and all the engineering that went into the design (thanks James). This is just the beginning of a life-time of learning how to cook in it. I think all of us went through the first few firings that uneasy feeling that it doesn't work....but it's just the oven drying-out. It will get better and better until it dries out completely. have fun John

[david s]

Re: Underfloor heatloss with ceramic fibre board - what temps do you register?

You can usually feel with your hand that the outside feels a bit damp when you are curing it, another more accurate way is to place some plastic over the outside and see if there is any moisture on the underside of it. Also the moisture near the base of the dome and that under the floor seems the last and most difficult to remove. It takes way longer than you would think (about 8 firings after you've finished the initial weeks curing) to remove the moisture completely. Keep firing and cooking and you'll be fine.
Dave