sedox
New Member
Posts: 3
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Post by sedox on May 26, 2013 13:12:26 GMT
Hi all, I'm half way through building my oven and will post some pics soon. For now I have built the base and brickwork and put in a 3" concrete slab which will be ready to finish with the oven in a few days.
I need help with the following:
I have a 2" gap from the top of my concrete base to the level of the shuttering, I plan on building this up with 2" of vermacrete mix but is 2" enough? Having only read about using anything other than concrete for the slab, this is a last minute addition. I am finishing the slab with fire bricks anyway so not sure if the vermacrete will be a useful addition?
Thanks.
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Post by cannyfradock on May 26, 2013 16:27:45 GMT
Hello Sedox.... welcome to the forum.
There should always be a thermal layer between concrete slab and fire-brick hearth. Most members use a minimum of 4" of vermecrete...or 4" of insulation block (thermolite or celcon etc...laid flat).
I would say that 2" is NOT enough....purely because the heat from your hearth may penetrate just 2" of vermecrete and if so the concrete would act as a heat sink drawing the saturated heat from your hearth. Try to get as close to 4" as you can.
Terry
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sedox
New Member
Posts: 3
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Post by sedox on May 26, 2013 16:47:07 GMT
Ok, what I may do is put the 2" in and build up an extra bit on the area where the oven will sit, making 4"
Is there a volume calculation I can use to work out how many litres of vermiculite I will need to make up enough vermacrete? Lets say I have 1m2 to fill with 10cm of vermacrete........
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Post by cannyfradock on May 26, 2013 16:55:13 GMT
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Post by tonyb on May 27, 2013 10:57:16 GMT
Sedox as Terry says, the purpose of the insulation layer is to stop heat being sucked away by the concrete layer, which to me is more about increasing efficiency and as such is desirable but not necessarily essential. Should the layer be 2, 3, 4, more? The more you have in place the more better from a thermal efficiency perspective but there is an associated cost. When designing the oven if you go with thermalite blocks, since they come in standard sizes you'll get 100mm thickness (assuming you place them on their side  ) but I wouldn't necessarily say that automatically means you need to have 100mm thickness if you are using vermicrete. |
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Post by bookemdanno on May 28, 2013 12:08:33 GMT
Like the guys say, if you can get 100mm and suffer having to adjust by 50mm, that's the way to go.
You can get 75mm and in some places 50mm Thermolites too.
But, they're not tried and trusted by UKWFOForum members.
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sedox
New Member
Posts: 3
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Post by sedox on May 28, 2013 12:24:33 GMT
Have decided to go with a layer of 4" thermolites.
Any recommendations on the mortar to use to set these to my concrete base?
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Post by bookemdanno on May 29, 2013 13:05:08 GMT
Just normal... Soft sand, cement, lime and a touch of plaz in your water...about 7:1:1. Mix for plenty of time, till nice and fluffly. Like Cake mix. Take a bit onto your trowel, tap it, and invert it. If it still sticks, you're ready to cook. Soak the blocks well, as they're pretty thirsty. If you've got a nice flat base, and a large notched trowel (10mm notches) you can lay them like big thick tiles!  |
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Post by rivergirl on May 29, 2013 16:03:56 GMT
Welcome to the forum, looking forward to the piccies
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) but I wouldn't necessarily say that automatically means you need to have 100mm thickness if you are using vermicrete.
