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Post by pizzapaul on Jun 1, 2020 5:56:33 GMT
I have been re-reading this thread and there has been discussion about potential issues of trapped moisture, foil linings etc.
Line with aluminium foil or not?
If so pierce the foil to allow moisture to escape?
What about the final vapour barrier - surely that is meant to be, well, a vapour barrier?
Piercing the vapour barrier seems counterintuitive?
Thoughts from the experts?
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Post by truckcab79 on Jun 1, 2020 6:39:01 GMT
Well. I’m no expert but I was advised to pierce both the foil layer and the vapour barrier but like you I concluded rightly or wrongly that it made no sense and the opinion of POS was the same so I left it unpierced. Clearly opinion varies but my oven performs well so I’m happy with what I did. Do what feels right. There will always be someone on any forum ready to tell you you’ve done it wrong.
I’ve seen several builds where they build in a vent. Essentially a tube from the dome, through the insulating layers to the outside. Again I can see the theory of how that lets vapour out without piercing the whole vapour barrier but concluded that the vent would struggle to be effective unless you installed multiple numbers of them around the dome.
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Post by webbm00 on Jun 1, 2020 7:09:03 GMT
I didn't add foil or the vapour barrier on my Milano 750 build but as mines in a shelter it's wont get rained on. As truckcab says there will always be differing opinions.
The one thing I would advise is put as much insulation under the oven as you can. I only added 25mm of calcium silicate board under mine and it's where the majority of the heat is lost. And you can't fix it after it's built!
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Post by pizzapaul on Jun 1, 2020 13:20:53 GMT
The one thing I would advise is put as much insulation under the oven as you can. I only added 25mm of calcium silicate board under mine and it's where the majority of the heat is lost. And you can't fix it after it's built! Interesting comment on the insulation **under** the build. I wasn't planning on anything more than I have already eg; putting base onto the existing brick/block. My oven will be outside and is I put calcium silicate under the oven then I will struggle to keep it dry - which was want happened with my old DIY build. Once the board gets wet I think it will conduct heat very well :-) Anyone else with thoughts on the insulation under the build? (By the way, I am going with keeping moisture out rather than worrying about keeping the existing moisture in - rightly or wrongly! No piercing here) |
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Post by truckcab79 on Jun 1, 2020 13:29:19 GMT
Nothing under mine other than the base, slabs and lintels. Still performs well and retains heat until the next day. Not to say it couldn’t be improved of course and as pointed out you certainly can’t add it afterward.
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Post by albacore on Jun 1, 2020 13:34:30 GMT
The fire sits directly on the floor of the oven. If you don't have any insulation under the base, whether it be firebrick, refractory or whatever, you will have massive heat loss by conduction.
The oven will work, but not particularly well. As webbm00 says, put plenty of insulation there - at least 50mm of calsil.
And I must be one of the few crazy souls who DID retrospectively fit more insulation underneath - but it's certainly a procedure to avoid!
Lance
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Post by pizzapaul on Jun 1, 2020 14:09:38 GMT
The fire sits directly on the floor of the oven. If you don't have any insulation under the base, whether it be firebrick, refractory or whatever, you will have massive heat loss by conduction. The oven will work, but not particularly well. As webbm00 says, put plenty of insulation there - at least 50mm of calsil. And I must be one of the few crazy souls who DID retrospectively fit more insulation underneath - but it's certainly a procedure to avoid! Lance That does make a lot of sense. I might have to pause starting my build until I have thought more about this! I should be able to add some insulation under my base but I would rather not use board because of it getting wet and strength - its going to have a heavy kiln on top of it. So best to use a layer of insulating bricks? Refractory? Fire bricks? Or will calcium silcate board be ok? Could I do a mix of my own and pour it myself? I have a brick base where I could easily remove a load of the bricks to make way for an insulation layer. In other words replace existing bricks with insulation but leave surrounding bricks |
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Post by albacore on Jun 1, 2020 16:17:22 GMT
Refractory and firebrick are NOT insulating - quite the opposite, in fact. They are designed to retain heat.
You can make your own insulant known as vermicrete from vermiculite and cement. It is a poor substitute for more modern materials (you will need twice the thickness for the same effect) and takes ages to dry out once in place. You will find many articles on it on UKWFO.
Calcium silicate board has good compressive strength and will stand the weight of an oven.
I don't understand your getting wet concern; my oven is standalone and lives outside. I put a waterproof cover over it in the winter and it is fine and dry.
Lance
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Post by pizzapaul on Jun 1, 2020 16:32:43 GMT
Calcium silicate board has good compressive strength and will stand the weight of an oven. I don't understand your getting wet concern; my oven is standalone and lives outside. I put a waterproof cover over it in the winter and it is fine and dry. I will try to source some board and fit that under where I am planning to put the base. Easy to do at this stage as I was just about to fill the space with more bricks. I will fit board instead! I felt that the board might get moisture from the surrounding brickwork etc unless the whole area was covered/waterproof. But I am willing to give that a go. So glad I asked and got this thread going again! Thanks everyone |
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Post by truckcab79 on Jun 1, 2020 19:44:38 GMT
Didn’t use it myself but have read plenty of threads on people getting calcil board wet and it turning to mush. Think it’s only an issue if you get it wet during the build. Soon as it’s covered you’re good to go.
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Post by pizzapaul on Jun 1, 2020 21:15:23 GMT
Didn’t use it myself but have read plenty of threads on people getting calcil board wet and it turning to mush. Think it’s only an issue if you get it wet during the build. Soon as it’s covered you’re good to go. If not calcil board (because it may or may not go to mush) and not refractory/fire bricks (heat retaining rather than insulating) then any other 'solid' insulating ideas for under the base? I have read one article that recommends broken glass covered with sand! |
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Post by webbm00 on Jun 1, 2020 21:29:16 GMT
Didn’t use it myself but have read plenty of threads on people getting calcil board wet and it turning to mush. Think it’s only an issue if you get it wet during the build. Soon as it’s covered you’re good to go. Calcium Silicate board soaks up water really well but if you cut it to the shape of your oven base and cover it in foil before putting it under your oven it will be ok. Remember that once you build up around your oven to the cooking floor height and apply the insulation and render to the dome you will have covered the calcium silicate board completely |
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Post by pizzapaul on Jun 2, 2020 6:19:12 GMT
Thanks. Here is a picture to illustrate the build. This is the base of my old oven. I took out the refractory bricks etc and now want to fill in with insulation before putting the Milano 750 base over the whole area. I might remove a few more bricks depending on exact dimensions. You get the idea though. I have found insulating fire bricks and they look like them will work well here? Insulating firebricks - not regular "heavy heat sink" firebricks. Like this : shop.vitcas.com/insulating-fire-bricks-vitcas-grade-23.html |
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Post by albacore on Jun 2, 2020 8:10:50 GMT
They would probably work. The insulation value will be about half as good as calsil for the same thickness and you will get more heat loss because of all the edge spaces between the bricks.
Also check out Ebay for calcium silicate board - sometimes the prices are good. Also search for Skamol, but check grade.
Lance
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Post by pizzapaul on Jun 2, 2020 11:23:53 GMT
They would probably work. The insulation value will be about half as good as calsil for the same thickness and you will get more heat loss because of all the edge spaces between the bricks. Also check out Ebay for calcium silicate board - sometimes the prices are good. Also search for Skamol, but check grade. Lance Thanks again Lance. I have gone for insulated bricks. Got a good price delivered (I think) and I feel they are less 'fragile' in my rustic environment! 76mm bricks so will give some insulation anyway, even according to this shop.vitcas.com/blog/what-you-need-to-know-about-insulation.htmlI was just about to built without any insulation so you all saved me there!! |
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