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Post by downunderdave on Mar 6, 2017 12:22:01 GMT
Depending on conditions of course, but normally clay takes around one week/ inch of thickness to dry, so be patient. Thanks Dave, that's a useful stat to know, looks like I've got at least another couple of fairly dull weeks of tea lights and tiny fires to go...! I don't know how big your oven is or what volume the thickness of your dome would be, but if around 25% of clay in its plastic state is water, then you are probably looking at trying to eliminate more that 30 litres of water. How long and with how many tea light candles do you think you could boil dry a 30 litre container of water? I'm suggesting that the tea light candles are next to useless. Drying clay is dependant on air velocity, temperature and humidity. None of which are particularly useful in your part of the world at this time of year, but sun and wind if available will dry it out the best and safest. In Australia for oven drying we use what we call heat beads, which are coal barbecue fuel like briquettes , they do a good job because they don't flame up giving you direct flame impingement on the inside of the dome. You'd probably need around 30 kg or more (much better than 30 kg of tea lights, but not as pretty
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Post by dave36 on Mar 7, 2017 8:37:30 GMT
Thanks Dave, that's a useful stat to know, looks like I've got at least another couple of fairly dull weeks of tea lights and tiny fires to go...! I don't know how big your oven is or what volume the thickness of your dome would be, but if around 25% of clay in its plastic state is water, then you are probably looking at trying to eliminate more that 30 litres of water. How long and with how many tea light candles do you think you could boil dry a 30 litre container of water? I'm suggesting that the tea light candles are next to useless. Drying clay is dependant on air velocity, temperature and humidity. None of which are particularly useful in your part of the world at this time of year, but sun and wind if available will dry it out the best and safest. In Australia for oven drying we use what we call heat beads, which are coal barbecue fuel like briquettes , they do a good job because they don't flame up giving you direct flame impingement on the inside of the dome. You'd probably need around 30 kg or more (much better than 30 kg of tea lights, but not as pretty Cheers Dave, fair point, I guess I'm looking at 20kg / litres of water as have 70ish kg of clay in the oven (70kg clay, 140kg of sand, 8cm thick walls). Not a job for tea lights alone. I guess it it will be more than a few weeks to allow some natural drying (albeit its only about 10 degrees at the moment) and I can pick up some heat beads on the weekend (it appears some UK shops stock them). I guess I will just have to patient, quite fancied finishing by May, but if it takes longer than so be it. Will take care not to over egg the use of heat beads, suspect could end up with cracks if I use too many too early. dave
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Post by dave36 on Mar 11, 2017 9:34:25 GMT
So, on the advice of downunderdave am now using heat beads (charcoal briquettes) and they work really well. Nice even heat, no flames, can get them temp up much higher than with tea lights. Currently heating up to c 40degrees and will keep moving the temp upwards. After almost two weeks, dome feels fully dry but have no doubt there's a lot more water lurking in there to expel. Chimney starter is v useful to get the briquettes started.
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Post by downunderdave on Mar 11, 2017 11:10:52 GMT
When firing a moist oven it is normal to have difficulty keeping the fire alight. This is a good indication that there's still water present.. when you've burnt plenty of heat beads and you think the thing is pretty dry, start throwing small bits of wood in, but try not to let direct flame impingement on the dome. This will increase the temperature and drive more moisture out. You will then get to a point where the black soot begins to burn off the top of the inside of the dome. Be careful here because most steam spalling occurs between 250-300 C, (carbon burns off at around 300 C) so don't rush it. There will be a persistent ring of black soot around the base of the dome indicating it's moist and cooler there. When it is finally all burnt off you've chased all the moisture out and the oven can be fired up much faster safely with much less fuel. When doing all this you should also cook something in it, try roasting a chicken or two, you won't be disappointed.
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Post by dave36 on Mar 12, 2017 14:19:57 GMT
Door done...50mm ceramic fibre board (left over), 40mm Oak, former covered in aluminium flue tape (not sure if this will survive, but for a fiver a roll, let's see what happens). Killing time whilst drying out the clay...
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Post by oblertone on Mar 13, 2017 8:09:58 GMT
Neatly done on the door; however I've always thought introducing wood to a fire will only go one way ! Happy to be proved wrong.
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Post by downunderdave on Mar 13, 2017 9:31:45 GMT
Neatly done on the door; however I've always thought introducing wood to a fire will only go one way ! Happy to be proved wrong. I've persisted with a wooden door for my ovens because functionally it's not a bad insulator and it's traditional, Italian ovens have used wooden doors for centuries. Aesthetically I think it looks really nice too. The trick with a wooden door is to keep the heat from cooking the door. An insulating panel will do this, to a certain extent, but if you think you can place the door after cooking pizzas to retain heat for the next day, you'll probably find the door will be burnt the next morning. However if you only use the door for baking and roasting temperatures (< 300 C) it's fine. Alternatively if you have a steel or aluminium door they are both highly conductive and will tend to suck heat out of the structure, not to mention that they get dangerously hot to handle.
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Post by dave36 on Mar 18, 2017 0:58:07 GMT
Cheers Dave, noted re max temp for a wooden door. Guess i can use a spare breeze block cut to shape if I need a high temp version. Otherwise, after two weeks of smallish fires I am now on to medium fires. Temperature getting up to 250-300 Celsius, using briquettes and wood (bought half a pallet of kiln dried today, hurray), only a couple of small cracks thus far. Planning another couple of weeks of this, say get temp up to min of 400 before fire blanket and render goes on (I wonder if this is realistic, exterior of dome today was 100 Celsius with interior being 220ish, i.e. plenty of heat loss). Thoughts on when best to blanket up and render very welcome- current thinking is earlier of hitting 400 or when black soot disappears. Photo attached. Ps- is very pleasing to see how the air draws in at the bottom and smoke pushes out at the top, mostly but not all, through chimney.
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Post by dave36 on Apr 2, 2017 15:15:57 GMT
Hi all- an update and a question....hurray, the soot is finally burning / burnt off the inside of the dome (Christ, this thing gets hot. No hairs left on my left arm...). Exterior cracks seem to have settled down to the same cracks just opening a little each time. I've found a squirt of heat resistant sealant right into the crack whilst the dome is still hot works well (way too hot to get some clay in), followed by the usual wet clay when the temperature is more manageable. The question, I have a few 2-3mm internal cracks in awkward places. Any bright ideas on how to fill? I can feel my way around, but it's sorta tricky. Thought I'd ask, but guessing there may not be a neat solution. Actually a second question...I'm now confident the clay dome is dry (been a month and had a couple of fires with soot pretty much gone from the inside). Was going to insulate in a week- any thoughts or reasons I should delay? Thanks as always! Dave
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Post by jagnut on Apr 2, 2017 17:58:42 GMT
PUT a mirror in the oven and repair the crack that way, then you will be able to see what you are doing easy!!!!. or lay on your back and crawl in the door opening .
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Post by dave36 on Apr 13, 2017 6:53:51 GMT
Thanks Jagnut, mirror worked a treat and now cracks sealed (for now). Insulation is now on and base coat of K-Rend applied. Getting close to finishing, hurray....
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Post by jagnut on Apr 13, 2017 20:23:02 GMT
Hi dave36 how did it go with the k render, need to pick your brains with this k render am just waiting for my vermiculite to dry out .Did you use a base coat or just a top coat or both and does it go a long way with the bags. By the way you have done a nice job on your oven looks great its nice watching the oven being finished . cheers jagnut.
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Post by dave36 on Apr 14, 2017 7:01:20 GMT
Hi dave36 how did it go with the k render, need to pick your brains with this k render am just waiting for my vermiculite to dry out .Did you use a base coat or just a top coat or both and does it go a long way with the bags. By the way you have done a nice job on your oven looks great its nice watching the oven being finished . cheers jagnut. Jagnut I found the K Rend really easy to use (and this was only the second time I have rendered). I used HPX base as I was rendering onto insulation / chicken wire, although I suspect I could have skipped the base coat. My sense is that you could skip the base coat (it's quite dear) as you're rendering onto a firm surface. The oven is 1m (exterior) diameter and it took 1 bag of base to get 6mm-ish deep if base coat. I then applied two bags of top coat (terracotta colour) to add another 12mm or so and had a little left over, so three bags in total. Top coat also easy, but one point to note, if you buy coloured KR, be wary of the colour - the two bags I used were very different in colour, but not an issue as could spread the second bag completely over the first (so suggest don't do the oven in two halfs, go one layer over the other). If you want more info check out the Amaroc.co.uk website, they have some useful info on Krend, how to apply etc. nice build btw, dave
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Post by jagnut on Apr 14, 2017 20:07:22 GMT
Hi dave36 how did it go with the k render, need to pick your brains with this k render am just waiting for my vermiculite to dry out .Did you use a base coat or just a top coat or both and does it go a long way with the bags. By the way you have done a nice job on your oven looks great its nice watching the oven being finished . cheers jagnut. Jagnut I found the K Rend really easy to use (and this was only the second time I have rendered). I used HPX base as I was rendering onto insulation / chicken wire, although I suspect I could have skipped the base coat. My sense is that you could skip the base coat (it's quite dear) as you're rendering onto a firm surface. The oven is 1m (exterior) diameter and it took 1 bag of base to get 6mm-ish deep if base coat. I then applied two bags of top coat (terracotta colour) to add another 12mm or so and had a little left over, so three bags in total. Top coat also easy, but one point to note, if you buy coloured KR, be wary of the colour - the two bags I used were very different in colour, but not an issue as could spread the second bag completely over the first (so suggest don't do the oven in two halfs, go one layer over the other). If you want more info check out the Amaroc.co.uk website, they have some useful info on Krend, how to apply etc. nice build btw, dave Cheers for that dave36 am in france at present just checking out emails ect before the beer, just a quick question so is you oven in total around 4 sq meter say .just trying to work out the total of bags to order, and by the sounds of it leave out the hpx base coat?. cheers dave
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Post by dave36 on Apr 15, 2017 5:50:55 GMT
Jagnut I found the K Rend really easy to use (and this was only the second time I have rendered). I used HPX base as I was rendering onto insulation / chicken wire, although I suspect I could have skipped the base coat. My sense is that you could skip the base coat (it's quite dear) as you're rendering onto a firm surface. The oven is 1m (exterior) diameter and it took 1 bag of base to get 6mm-ish deep if base coat. I then applied two bags of top coat (terracotta colour) to add another 12mm or so and had a little left over, so three bags in total. Top coat also easy, but one point to note, if you buy coloured KR, be wary of the colour - the two bags I used were very different in colour, but not an issue as could spread the second bag completely over the first (so suggest don't do the oven in two halfs, go one layer over the other). If you want more info check out the Amaroc.co.uk website, they have some useful info on Krend, how to apply etc. nice build btw, dave Cheers for that dave36 am in france at present just checking out emails ect before the beer, just a quick question so is you oven in total around 4 sq meter say .just trying to work out the total of bags to order, and by the sounds of it leave out the hpx base coat?. cheers dave Jagnut It's about 2.3m square. Can calculate as 2x3.14 x radius x radius. Then I'd add 10pc as you dome probably won't be perfect half sphere as you ( i assume) have built the dome on your hearth and will be rendering down to under hearth insulation level. Krend works out at about 1 bag per metre square to a 16mm depth (which is the recommended minimum, if memory serves). I'd skip the base coat as you're rendering onto a 'normal'surface. Dave
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