Mobile Community Oven Build In UK

[badrobot]

I buy all my refractory products from these guys , very good prices and very helpful https://www.castreekilns.co.uk/casta...ctory-56-c.asp

Thanks for the tip Fox.

Oddly enough the 'very helpful' company you mentioned was the same 'pretty helpful' guy I mentioned, James Castree. Kudos James. Good prices, agreed. though he had heard of, and sells SS needles he had never heard of said fibres but was very interested, don't be surprised if he starts selling them. Requested the data sheet from these guys to see if there are fibres in the castable. Can't ask manufacturers as they are in plain white bags. I will wait for clarifacation and buy fibres seperately if necessary.

Getting closer

[fox]

I buy all my refractory products from these guys , very good prices and very helpful https://www.castreekilns.co.uk/casta...ctory-56-c.asp

[david s]

Pi There’s no symbol on my key board for the Greek letter. It is 3.142
The salesman probably has no clue. Try looking at the data sheet on the product, it may tell you if there are fibres in it, or try ringing the manufacturer. You can also sieve a sample to see if there are fibres there.

[badrobot]

If you use a proprietary castable refractory then the burnout fibres should already be in the mix so you won’t have to add them. If you make your own castable with either homebrew or CAC then it is wise to add them. Only a handful for every 20 litres of dry castable is required but they must be dispersed well, which requires some extended mixing. It is only the fine hairlike fibres that should be added, not the longer thicker ones. The addition of stainless needles is not mandatory. They will improve strength and crack resistance, but make handling the mix more difficult the addition is 2-4% by weight. Most manufacturers don’t add them because of the added expense and handling difficulties. FB don’t, or at least they don’t advertise that they do, so assume they don’t.
The normal procedure for insulation is one or more layers of 25 mm blanket over which a layer of 10:1 vermicrete is applied. This produces a firm substrate over which can be applied a stucco finish that can then be waterproofed if you wish. Working straight over the blanket is difficult because it’s a bit soft and the surface is lumpy.

Formula for working out volumes is V=4/3 x Pi x r3 (volume of a sphere) calculate volume ofspher using radius to outside, then subtract volume of sphere using internal radius. Halve the result because it’s a hemisphere.

Thats great thanks. Spoke to supplier earlier and the castablwe they sell didnt seem to have fibre in it or at least the pretty helpful guy had never heard of it. Awaiting a call back from Sika UK regards sourcing some but can easy gets hold of some online I think (unbranded.)

Might need to work on that formula cos I don't gets it. 4/3? r3

[david s]

If you use a proprietary castable refractory then the burnout fibres should already be in the mix so you won’t have to add them. If you make your own castable with either homebrew or CAC then it is wise to add them. Only a handful for every 20 litres of dry castable is required but they must be dispersed well, which requires some extended mixing. It is only the fine hairlike fibres that should be added, not the longer thicker ones. The addition of stainless needles is not mandatory. They will improve strength and crack resistance, but make handling the mix more difficult the addition is 2-4% by weight. Most manufacturers don’t add them because of the added expense and handling difficulties. FB don’t, or at least they don’t advertise that they do, so assume they don’t.
The normal procedure for insulation is one or more layers of 25 mm blanket over which a layer of 10:1 vermicrete is applied. This produces a firm substrate over which can be applied a stucco finish that can then be waterproofed if you wish. Working straight over the blanket is difficult because it’s a bit soft and the surface is lumpy.

Formula for working out volumes is V=4/3 x Pi x r3 (volume of a sphere) calculate volume ofspher using radius to outside, then subtract volume of sphere using internal radius. Halve the result because it’s a hemisphere.

[badrobot]

"
Rob,
I use castable refractory which is a blend of CAC (calcium aluminate cement), high temperature aggregates and burnout fibres which assist in water elimination during initial firing. The stuff is expensive and you need to do a calculation of how much is required. As it’s rated to 1450C it uses high temperature aggregates that are way in excess of what we require. The use of lime in conjunction with CAC is a no no because it acts as an accelerant reducing the already limited working time of the mix. The stuff is also very temperature dependant. There are recipes out there (including this site) that recommend CAC and lime together. Unfortunately those that attempt it will find their mix going off as soon as it’s been mixed.Another alternative that works (just) for our temperature range is what we call homebrew. It is used as a mortar for brick builds and can be used as a castable. It is 3:1:1:1 sand, hydrated lime, Portland cement and powdered clay. Very cheap and good working time, but the lime is vicious on the hands, wear rubber gloves. It also requires the addition of the burnout fibres which can be the really fine polypropylene ones used in reinforcing concrete. They are finer than human hair and take extensive mixing to disperse in the mix properly. I also use them for adding to mortar if brick building as they provide some measure of reducing steam spalling wher mortar joints can be extremely thick.
Regarding my mobile, it sits on a timber trolley that has 6 wheels that enable me to roll it on and off the trailer easily.
On the subject of information sharing, most of us here are old farts and well beyond wanting to keep secrets in order to build empires. Rather, we are excited by the enjoyment of cooking by fire in ancient yet highly efficient designs and we want to “spread the love”.

Dave"


Hi Dave, I don't get to write here everyday so please excuse me if it seems long.

I can locate CAC here (Ciment fondu) though sourcing appropriate aggregate might fare a little more tricky, though not out of the question yet as I will try a few more places this week. I may just go with ref castable with 42% aluminate aggregate already in it for convenience. I will now be opting to keep mobile oven small-ish. (I read somewhere that your oven is 21"-is that inside measurement surely) alot smaller than the one I was planning originally (approx 750mm internal) but after much consolidating of the variables. I am now aiming at an oven around 600mm internal max-smaller if I feel I can get away with it.

I am thinking 50mm thick ref castable + adding the novomesh 950, (around 2%/100ml per 100litres of mix?) The polyprop fibres all melt out at 160C and in this application are only to aid the elimination of moisture through the curing process right. Do you think I need to add SS needles too, that is the question?

Finishing with a 50mm layer of fibre insulation blanket, covering dome and flue gallery, wire to secure it then 3 watered down layers of flexible acrylic pointing cement painted on surface leaving an expansion joint at the brick arch junction to allow for fluctuations. Would you be able to provide an example of the one you did or similar.

I am not entirely sure how best to figure out calculating amounts based on the sizes stated. I was told 2000kg per M2 but still a bit confused how to apply this info. Is there a formula I need to work with or a easy method with which to go forth?
I am definitely keen to avoid the tendancy to make an oven unecessarily big, after all a pizza shouldn't take that long to cook once heated, so cooking one 12" pizza at a time is fine. I actually opt for and prefer the opportunities it brings to enable people to prep, cook & eat together. You will be glad to know I not aiming for world domination here, Though I do appreciate the purist 90 second multi pizza brick oven view/approach too, and aspire to operate at around 450-500C. I have built a cob oven and operated a pompie esque oven before. So experience helps.

How does all that sound to you?

[UtahBeehiver]

That's a good one, so I will remember that next time I am in Aussie land

[david s]

I heard about both of those aging techniques as well as peeing on the copper too, neighbors would turn me in, haha

When an American is “pissed” he’’s usually pretty angry.
When an Australian is “pissed” he’s usually pretty happy.

[UtahBeehiver]

I heard about both of those aging techniques as well as peeing on the copper too, neighbors would turn me in, haha

[david s]

Thanks Dave....It seems that many take this initial approach only to regret it later (5:1 vermcrete). I did see the uk forum you mentioned, I will check it out again thanks, I see you are also part of that uk forum? I love your set up and ingenius method of fixing it down/mounting to base and then trailer. Is that on rubber feet? Is refractory cement/hydrated lime and SS needles the way to go then you think? ifso what ratio would you recommend as aiming for the similar set up as yours, (the one with flames on side.) I thought adding lime was toxic for some reason. The research cont.

Regards Rob

Rob,
I use castable refractory which is a blend of CAC (calcium aluminate cement), high temperature aggregates and burnout fibres which assist in water elimination during initial firing. The stuff is expensive and you need to do a calculation of how much is required. As it’s rated to 1450C it uses high temperature aggregates that are way in excess of what we require. The use of lime in conjunction with CAC is a no no because it acts as an accelerant reducing the already limited working time of the mix. The stuff is also very temperature dependant. There are recipes out there (including this site) that recommend CAC and lime together. Unfortunately those that attempt it will find their mix going off as soon as it’s been mixed.Another alternative that works (just) for our temperature range is what we call homebrew. It is used as a mortar for brick builds and can be used as a castable. It is 3:1:1:1 sand, hydrated lime, Portland cement and powdered clay. Very cheap and good working time, but the lime is vicious on the hands, wear rubber gloves. It also requires the addition of the burnout fibres which can be the really fine polypropylene ones used in reinforcing concrete. They are finer than human hair and take extensive mixing to disperse in the mix properly. I also use them for adding to mortar if brick building as they provide some measure of reducing steam spalling wher mortar joints can be extremely thick.
Regarding my mobile, it sits on a timber trolley that has 6 wheels that enable me to roll it on and off the trailer easily.
On the subject of information sharing, most of us here are old farts and well beyond wanting to keep secrets in order to build empires. Rather, we are excited by the enjoyment of cooking by fire in ancient yet highly efficient designs and we want to “spread the love”.

Dave

[david s]

Russell, if you want that green look you can accelerate the reaction by painting it with white vinegar. Another trick to give concrete sculptures an aged look is to paint them with yoghurt.

[UtahBeehiver]

Thanks for the compliment. All the copper shingles were hand cut and bent by me using tin snips and hand bender. I am just now starting to see some green patina (built in 2012) and will be pushing up tulips by time the whole oven is green.....lol

[badrobot]

Hi, Yes I have just joined this, and another forum regards not falling prey to avoiding such shoddy application/s. There are so many strange videos. I have certainly taken on board what Dave has imparted for sure. I know sound advice when I hear it.

And freakin WOW, your project is dope. I mean really wow. I was so excited and impressed looking through album documenting process, And the copper icing on the cake! Real tight craftmanship. Have you got verdigris burns yet-lol. Had you intended/considered this? (I think that sort of patina will only add to the beauty btw!)

Regards Rob

[UtahBeehiver]

I agree with Dave on usage of V or Pcrete as your core dome cast material. There are some questionable YouTube videos out there advocating using this mix as the main dome structure. We see people posting to this web site who want to head this direction and we try to explain that this mix is not structurally sound enough and should be used as a insulation material only. We very rarely see follow-up from these builders on the status of the project.

PS Follow DavidS's advice, he does cast oven commercially in Aussie land.

[badrobot]

Thanks Dave....It seems that many take this initial approach only to regret it later (5:1 vermcrete). I did see the uk forum you mentioned, I will check it out again thanks, I see you are also part of that uk forum? I love your set up and ingenius method of fixing it down/mounting to base and then trailer. Is that on rubber feet? Is refractory cement/hydrated lime and SS needles the way to go then you think? ifso what ratio would you recommend as aiming for the similar set up as yours, (the one with flames on side.) I thought adding lime was toxic for some reason. The research cont.

Regards Rob