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Lip on dome bricks using a tramell

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  • #46
    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.
    Kindled with zeal and fired with passion.

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    • #47
      Thanks for the guidance David

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      • #48
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        • #49
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          • #50
            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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            • #51
              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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              • #52
                Think how long it would take for a saucepan to boil dry with one tiny hole in the lid. It should relieve steam pressure build up but drying wet insulation takes a long time. As the heat rises by convection in the chamber the top of the dome will get hot and dry much faster than the bottom. I believe moisture vents are far better placed in the supporting slab and lining up with the dome insulation layers which will dry the oven more efficiently and be out of sight. My diagram explains how it works.

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                Last edited by david s; 05-16-2024, 12:41 AM.
                Kindled with zeal and fired with passion.

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                • #53
                  Thanks David,
                  OK your reasoning sounds good. But that looks like I should have provided those weep holes at the beginning of the build. Also the whole dome sits on a solid concrete slab.
                  What do you think?

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                  • #54
                    You could drill some holes up through the bottom of your concrete slab starting with an 8mm masonry bit. But you won’t know where the steel reo is, so fingers crossed you don’t hit any. The holes can then be widened to around 12mm About 4 to locate the dome insulation layer and a few near the centre to allow the underfloor insulation to breathe. I’ve performed this operation with excellent results on a few ovens with wet bottoms.
                    Last edited by david s; 05-18-2024, 01:18 AM.
                    Kindled with zeal and fired with passion.

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                    • #55
                      Thanks David
                      I have done that, and I must say that I feel a lot happier now with that sorted.
                      I managed to only hit one reo
                      Have a great weekend

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                      • #56
                        Hi guys,
                        Trusting that you all are doing great, and those in the Northern Hemisphere are putting your ovens to good use.
                        I have made a mistake, I sealed my outside built oven but did not seal the chimney. We subsequently had a long period of lots of rain with the result that the bricks on the chimney have produced a lot of efflorescence.
                        I don't want to rush ahead and do something that will be harmful to the quality and appearance of the bricks.
                        Does anyone have sound advice on how to best clean them, as well as what to seal them with.
                        Would it be best to use a sealer with Silane/Siloxane in it, or a water based sealer.
                        Also it appears that the water has permeated into the surrounding dome bricks, would this mean that I must do another round of cool to hot fires to get the moisture out.
                        I would be glad to receive professional advise on this issue.
                        Have a great day and weekend.

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                        • #57
                          It sounds like you still have moisture in your oven. You can wire brush off the efflorescence, but it would be best not to seal the brick work yet. Avoid pizza temperature for now and just use the oven for roasting and baking. If there is a persistent black ring of carbon around the bottom of the inside of the dome, which I suspect you have, don’t have a raging fire or you can risk damage at this stage. To test if the oven is still purging itself of water, you can also throw some sheet plastic over it to see if moisture condenses under it. You can hurry up the drying process, but it will risk damage. You can’t go too slow and it’s far safer.Leave the sealing until you are perfectly sure the oven is dry.
                          Kindled with zeal and fired with passion.

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                          • #58
                            Thanks David
                            I was pretty sure that the oven was dry before the week or so of heavy rain. So I had tested it with a plastic sheet and it seemed fine, so I went ahead and sealed it with a Siloxane sealer, but not the chimney.
                            ​​ Since the rain there are dark "fingers" showing on the dome going back from the chimney. I will post a photo a bit later.
                            The efflorescence does not come off easily with a wire brush, someone suggested weak hydrochloric acid, then to neutralise it afterwards with baking soda???
                            I have not started using it yet as there is a delay in the granite slab I am wanting to lay in the front

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                            • #59
                              Damp"gingers" from chimney?

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                              • #60

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