#21  
Old 03-02-2011, 10:12 PM
Peasant
 
Join Date: Jan 2011
Location: Canada/Tanzania
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Default Re: Tanzania/Canada

Thanks Dave,

Anyone....how thick on the scratch coat and finnish coat?....buttressing needed for arch on vent walls?

Cheers SteveS.

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  #22  
Old 03-02-2011, 10:31 PM
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Default Re: Tanzania/Canada

If you dont provide sideways thrust (buttressing) to an arch it will fail, build some fancy brickwork to the side of the arch.
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  #23  
Old 03-02-2011, 10:35 PM
Peasant
 
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Default Re: Tanzania/Canada

Also....I forgot this question. I've read almost everything on the proceedure for curing. I'm on a bit of a time constraint! All of the dome has been complete for well over a week except the last 10 brick coarse and the keystone which was complete 5 days ago. I must return to Canada in 1 week. Just finnished the insulation yesterday. Hopefully I will start stucco today as well as continue on the chimney. What does anyone think of me starting to go slow with the curing process now so it can be done before I have to leave. I have no thermometer sooooo....if I burn some news paper and then close the door I should be able to keep working....right? Just don't know how long to burn it for to get it to 200 degrees F. The outside temperature here usually gets to about 95 degrees by early afternoon.

Cheers SteveS.
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  #24  
Old 03-02-2011, 11:18 PM
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Default Re: Tanzania/Canada

Steve, you should start the fires to eliminate the water from the oven before you do the stucco. Failure to do this often leads to cracks in the stucco layer because of expanding steam pressure. your insulation layer probably needs a week to dry. What has your weather been like? Has is had plenty of sun and wind on it ? You add lots of water to the insulation layer and it has to be removed slowly. Trying to do this job fast is a recipe for cracks.Not that cracks in the outer shell are that crucial, it is only a weather protection thing anyway. I have made the outer shell as thin as 10 mm but usually more like 15mm.
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  #25  
Old 03-02-2011, 11:24 PM
Peasant
 
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Default Re: Tanzania/Canada

Thanks Dave,

How about the newspaper question?

Cheers, SteveS.
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  #26  
Old 03-02-2011, 11:30 PM
Peasant
 
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Location: Canada/Tanzania
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Default Re: Tanzania/Canada

Also the weather here has been hot and dry but after every step I have kept all my work moist to let it dry slowly....it's just that the insulation layer is so thick! I agree it will take a while for that insulation layer to naturally cure slowly but I don't have the time.

Cheers, SteveS.
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  #27  
Old 03-02-2011, 11:43 PM
david s's Avatar
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Default Re: Tanzania/Canada

If you burn newspaper and close the door it will go out.
You have added probably 50 litres of water or more to that insulation layer. How much fire would it take to boil dry a 50 litre drum of water ? Lots. That's why it is better to let nature dry it out for you. Once the insulation layer has set, keeping it moist to increase strength is a waste of time because the cement in that layer is only there to hold the pumice in position so you can stucco over it. In fact 5:1 is probably way to much cement IMO because it just adds thermal mass where you don't want it. I f you have to start fires just keep it really low, glowing embers rather than flames. Can you use charcoal? just keep it going gently for as long as you can. Should be able to feel the moisture coming out on the outside with your hand.
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  #28  
Old 03-03-2011, 02:18 AM
Peasant
 
Join Date: Jan 2011
Location: Canada/Tanzania
Posts: 39
Default Re: Tanzania/Canada

Thanks Dave,

I love the charcoal idea. I have plenty of that. I also have a small hibachi grill that can hold the charcoal for the low slow burn so it is not just sitting on the oven floor.

Now I read that the idea is to cure the oven slowly which I understand lets the oven get used to to the natural expansion and contraction that occurs when you get the temperature up to 800-900 degrees and then as it cools back down to room temperature no cracking occurs.

What your suggesting is that since I'm on a tight time, keep the charcoal going at a sustained low temperature to drive out as much moisture as possible before starting to raise the heat/cool....right?

By the by, my thoughts on closing the door on the paper fire was to do that after the fire was out. I hope you don't think that since I'm below the equator, I think oxygen isn't needed for combustion...lol. Thanks again for quick reply and help on this!

Cheers, SteveS.
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  #29  
Old 03-03-2011, 04:20 AM
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Default Re: Tanzania/Canada

Yes,
Crank up that Hibachi and keep it burning constantly but gently, for a few days. Monitor the moisture on the outside, then progress to larger fires until you are satisfied that the moisturevhas gone. Then do the stucco, cover with cling wrap to keep it moist, for strength and you're done.
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  #30  
Old 03-03-2011, 07:36 AM
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Default Re: Tanzania/Canada

Quote:
but I don't have the time
Decide in haste, repent at leisure.

Think if you have time to rebuild it if you crank it up to temperature too early and get it full of cracks.
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