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Lip on dome bricks using a tramell

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  • TEDFB
    replied
    I was thinking about the pizza dome and moisture,
    If a bit of moisture happend to, get in the inner layers somehow without me noticing it and I made a fire, it would cause steam to build up, especially as I have waterproofed the render, this steam would obviously be able to cause damage to the dome
    Would it be feasible for me to drill a small hole on top of the dome, say 5 or 6mm diam. down to the ceramic layer to allow the steam to escape. Then keep it plugged with say a wooden dowl.
    Or am I way off course?

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  • TEDFB
    replied
    Hi guys,
    Above are some photos of my progress with the oven, including the inner door, the vermiculite layer, the final render, and the store room on which the oven is built.
    This storeroom gets hot when the sun shines on it, would a layer of vermiculite / cement and render work in solving this problem?
    Has anyone done this,? If so how should I go about it, without it collapsing after a while?
    Thanks again for all the input and support you guys have given me to reach this point.

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  • TEDFB
    replied
    Click image for larger version

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  • TEDFB
    replied
    Click image for larger version

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  • TEDFB
    replied
    Thanks for the guidance David

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  • david s
    replied
    Commercial render/stucco mixes are designed to be partly waterproof. This is to reduce transmission of moisture while still allowing them to be partly breathable.The evidence of this becomes apparent when adding water to them it is difficult to get the water to penetrate.Most commercial renders are cement based and come dry in bags. Some will have “poly modified” marked on them, but they are still a cement based render. You can use a 100% acrylic render, these come wet in a bucket, but are a much more expensive option. The layer should be reinforced and the most common method is to use chickenwire. However because it requires applying over a compound curve and the mesh needs to be in the middle of the layer, this operation takes ages. My solution is to use random Alkaline Resistant AR glass fibres. They are very easy to use, saves heaps of time, but they are expensive. Seek them out from the concrete countertop manufacturers.
    Renders are usually applied in two layers, but to save time I do it in one layer around 15mm thick. The bagged renders will also recommend a max thickness of around 10mm, but because of the fibre addition you can go thicker. Hydrated lime in the mix increases flexibility, an advantage when the layer is exposed to thermal expansion that won’t be even over its whole surface. Lime also has crack healing properties which is an additional advantage. Unfortunately it has been either removed or reduced in proportion in most commercial renders because of the safety issue, make sure you wear rubber gloves.
    A good brew is 4:1:1 fine sand, Portland cement, hydrated lime. This will not have any waterproofing however. That can be done by applying an impervious layer over the render later.
    Regarding wetting the vermicrete before application, I don’t bother because it will be absorbed almost instantly. As it is also going to want to draw moisture from the render layer. My solution is to trowel the surface until all tooling marks are gone, then wet sponge the surface, then wrap the whole oven in clingwrap sealing the whole thing. This seals the moisture in the outer layer. The evidence of a proliferation of moisture beads under the cling wrap that remain until it is removed, indicates a good moisture level is maintained. As the strength of anything made with Portland cement will be enhanced by extended damp curing, I give it a week before removal.

    I stress that this is just my approach, there are many solutions.
    Last edited by david s; 05-07-2024, 03:40 PM.

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  • TEDFB
    replied
    Sorry, I forgot to ask if I should dampen the vermiculite layer before rendering

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  • TEDFB
    replied
    Hey guys trusting that you are all doing great.
    I am about to put the rendering layer which needs to be waterproof over the vermiculite /cement layer
    I have read some ideas, but would like to know from you guys who have had experience in this matter.
    What is the best strong mixture I should use, and should it be done in two layers, and if so do I use the same mix for both layers and do I waterproof both layers.
    Comments would be welcome.
    I will still post some photos when my grandson visits and helps with that

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  • TEDFB
    replied
    Once again, thank you for your valued replies

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  • rsandler
    replied
    You can, though it's a pain getting stucco/render/plaster to stick to ceramic blanket, particularly the large clumps necessary to smooth out bumps in the blanket. I did it, more-or-less successfully, on my first oven, but it was an exercise in frustration. I have not done an oven with a vermicrete layer (I did an enclosure on oven #2), but by all accounts, including David S's comment above, a thin vermicrete layer gives you a good base for the final plaster layer.

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  • TEDFB
    replied
    If I have 3 layers of ceramic blanket, can I skip the Vermiculite layer on the dome

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  • david s
    replied
    A lot depends on how thick you make the layer. I use around 35mm thick 10:1 layer and give it a week of drying in ideal conditions before applying the render coat. 35 mm is usually enough to restore a perfect hemisphere that evens out the lumps and bumps of the blanket. If you need to go thicker do two layers with a week drying for each.

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  • TEDFB
    replied
    Hi guys how are you doing,
    I am slowly making progress with my oven. I have done the drying out of the dome with progressive fires. There were some (I think) minor cracks.
    My next Question is.... After I have fitted the ceramic blanket and plaster it with Vermiculite / cement, do I make another fire to dry out the Vermiculite plaster, or is it best to leave it a couple of days to dry? Basically because I will put a final layer of waterproof plaster on as the oven is outside, and I seem to think that the Vermiculite plaster will not dry if it is covered by the waterproof layer.
    Any advice on this will be appreciated.
    ​​​​​​​Enjoy your day

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  • TEDFB
    replied
    A big thank you to you guys who have taken the time to share your expertise and experience in this build, my knowledge in these matters is limited.
    I think that I will be using a lot of your advice and continuing with the project in the near future, and will keep you posted on what I have done.
    Have a great day

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  • david s
    replied
    Whatever you try, use will prove it successful or not so try it and report back.
    Whilst a thicker mild steel inner door panel will be less susceptible to warping it will also contribute to increased door weight. Both mild steel and stainless are very conductive, mild steel way more than stainless. The steel sides of the door also easily conduct heat from the inner panel to the outer one. Maybe this could be reduced by having the front and sides thinner with perhaps the sides perforated to reduce conduction.

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