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  #91  
Old 12-27-2013, 10:34 PM
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Default Re: Finally started

Gudday
Yes absolutely .... You have to let it dry naturally that insulation stops the heat like it should. Don't bother with keeping it damp at all for the cement it not a strong layer. On a positive note tomorrow's a heat wave in Brissy so 37C plus....that's a plus. But storms possible nearly every afternoon. So if you leave home it might pay to tarp it just in case.
Same problem with finding a larger flue in Brisbane saw me going brick in the end, sometimes there are disadvantages to living in a sub tropical area!
Regards dave
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  #92  
Old 12-28-2013, 02:36 AM
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Default Re: Finally started

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Originally Posted by cobblerdave View Post
On a positive note tomorrow's a heat wave in Brissy so 37C plus....that's a plus. But storms possible nearly every afternoon. So if you leave home it might pay to tarp it just in case.
Thanks Dave. I hear they have revised the heat wave from 37 to 34. Was thinking of going to the shops to be in the air conditioning, just not sure what is worse, the heat at home or the maddening crowds at the post Christmas sales.

Agree, already covered with a tarp in case of rain.
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  #93  
Old 01-02-2014, 12:56 AM
mnl mnl is offline
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Default Re: Finally started

Have slowly started to increase the size of the fires. Generally don't keep them going for a long time but the last one was not small. Don't want to push it too hard too quick, but can't feel any increase in temperature above ambient on the outside of the oven.
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Last edited by mnl; 01-02-2014 at 01:48 AM. Reason: Fix typos
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  #94  
Old 01-02-2014, 01:32 AM
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Default Re: Finally started

Gudday
The heat you feeling on the outside is due to the air spaces in your insulation being full of water and transferring the heat. The inside of your oven surface is now dry so the fires are, easier to lite, and now give you more heat for the fuel you use.
This is the critical point in drying you oven. ( notice I didn't say cure) the moisture will want to wick back to those dry parts. If you let the fires get to hot and to closely spaced this will not happen. That trapped water will turn to steam.1 litre of water will produce 1500 litres is steam. It's pretty powerful stuff .. They use it in power plants the world over. So it will crack you oven if you let it . Back off and let the moisture wick back do you can get ride of some more next fire. Let the sun and wind help you but the process is slow.
Then you be able to increase those fire to heat temper your oven.
Sunday due to be 39 C, and 20 knots of wind take the cover off and let that baby bake.
Regards dave
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  #95  
Old 01-02-2014, 01:56 AM
mnl mnl is offline
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Default Re: Finally started

Hi Dave

Apologies for the typo (now fixed), it should have read that there is no increase in temperature on the outside. Don't know if I'm not getting the fire hot enough or if the calcium silicate (sides) or ceramic blanket (top) that is between the oven and the vcrete is doing its job and not letting the heat into the vcrete to dry it out from the inside. Regardless, I think what you say is good pad vice and back off a bit and take it slow.

I knew that steam would be less dense than water but did not know it would be in 1500:1 sort of ratio.

Cheers

Mark
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  #96  
Old 01-02-2014, 12:28 PM
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Default Re: Finally started

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Originally Posted by mnl View Post

I knew that steam would be less dense than water but did not know it would be in 1500:1 sort of ratio.

Cheers

Mark
It gets worse. Say you manage to get your oven temperature up to 200 degrees centigrade before the steam manages to rupture everything and explode. At 200 degrees C, 1 litre of water would very much like 2157 litres of volume to occupy at one standard atmosphere (101.3 kPa).
If the volume can't expand and the steam is forced to occupy the same litre that the water occupies, then the pressure rises to 32 psi, if I've got the ideal gas equation correct.

Last edited by wotavidone; 01-02-2014 at 12:34 PM.
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  #97  
Old 01-02-2014, 02:05 PM
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Default Re: Finally started

Looking good Mark.Nothing beats looking at that fire belting away in the oven you created.How are the insulation bricks at the front?Are they stopping heat transfer effectively?
Keep up the good work.
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  #98  
Old 01-02-2014, 04:09 PM
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Thumbs up Re: Finally started

Quote:
Originally Posted by mnl View Post
Hi Dave

Apologies for the typo (now fixed), it should have read that there is no increase in temperature on the outside. Don't know if I'm not getting the fire hot enough or if the calcium silicate (sides) or ceramic blanket (top) that is between the oven and the vcrete is doing its job and not letting the heat into the vcrete to dry it out from the inside. Regardless, I think what you say is good pad vice and back off a bit and take it slow.

I knew that steam would be less dense than water but did not know it would be in 1500:1 sort of ratio.

Cheers

Mark
Gudday mark
It's a good thing that you can't feel the heat from the fires on the outside. It usually means that trouble is brewing or should I say boiling on the inside.
Drying fires dry out the surface of the oven brick any other water in the structure will then be sucked into the dry area by capillary action for you to again dry out. Slow but safe.
The ceramic insulation layer is a good thing to have too as it provides a flexible layer and an expansion space for any steam up to a point.
You might think of including a sealable vent to that ceramic layer. I have fitted one to my own oven and its a big help as all ovens including covered ones can get moist from time to time just from the humidity in the air.
Regards dave
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