30" cast pizza oven - scotland

[Daveholdn]

Hattori-Hanzo Thanks, I've loads of bricks to use here though so will try and work around those for the dome.

I daren't take the cover off my vermiculite slab at the moment as there is zero let up in the rain up here so can get a pic for update, but a question about insulation boards on top of the vermiculite hearth; I've ordered 2 x ceramic fibre boards but will have to join them to get the width desired. Has anyone joined CF board before and do I need to use any special sealant or tape? Also I am only using 1" board thickness to sit under my firebricks, will this be enough do you think? I am using slightly thicker fire bricks.

thanks again

Dave

[Hattori-Hanzo]

Just to add to the sand castle form comments, I used a load of polystyrene under the sand to reduce the amount needed. In the end I think I only used half a bag of sand but my oven is smaller.

Its easy to cut and shape, I held it in place with wooden cocktail sticks and it was a doddle to remove once the casting was done. If you're lucky to find some for free even better as to buy it's more expensive than sand.

Also a question to the pro's, if you plan to render your dome could you use plastering sand to build the castle that way you can reuse it for the render at a later stage?

[Daveholdn]

Mullster , cheers, I do, I have 200kg on order from MKM but was rethinking amounts, but aye, you need them at the same time don't you don't know where my head was at. Was thinking I could change order to 100kg of play sand for the mould and then what is left after, build a sand pit for the kids, but I think play sand is a lot finer and dryer and would be a nightmare to mould?
Cheers

[Mullster]

Cheers Mullster, good to know they look OK, in regards to the sand, I take it you used the same sand you used for your mould in the homebrew, or as much as you could salvage? And when you say you don't think the 104kg is correct, do you think I should add another 100kg on to take into account the mould?
Cheers again mate, your build thread has helped me out no end

Dave

Yes exactly the same type of sand - builders sand - the frustrating thing being you need it all at same time and then when the casting is set I’ll be left with 100kg of sand and nothing left to build .

So yes I think 200kg total is about right but didn’t you say you had 200kg arriving anyway in another post?

[Daveholdn]

Hi Dave - I’m a few weeks ahead and your quantities look about right to me except for the sand needed for the dome.

Personally my vermicrete slab had 3 weeks before I built on top but might not have been so long if I’d had the bricks sooner

Cheers Mullster, good to know they look OK, in regards to the sand, I take it you used the same sand you used for your mould in the homebrew, or as much as you could salvage? And when you say you don't think the 104kg is correct, do you think I should add another 100kg on to take into account the mould?
Cheers again mate, your build thread has helped me out no end

Dave

[Mullster]

Hi Dave - I’m a few weeks ahead and your quantities look about right to me except for the sand needed for the dome.

Personally my vermicrete slab had 3 weeks before I built on top but might not have been so long if I’d had the bricks sooner

[Daveholdn]

Hi Team,

So the form/shutter came off the vermiculite slab nicely leaving a big, square, 2 inch flapjack/granola bar! Now looking forward to the dome and gallery, I've decided against using refractory cement as I'd approx need 6 x 25kg bags which would kill the bank, so have decided to go for the home-brew option with added SS needles and polypropylene fibres!

Researching the forum, particularly the excel spreadsheet available, I have the following quantities calculated for a 30" internal dome, 2" thick, gallery height 9", length, 9.3: (all include 10% wastage factor)

Sand = 229lbs/104kg
Fireclay = 55lbs/25kg
Portland = 60lbs/28kg
Lime - 20lbs/9kg
SS needles - 10lbs/4.5kg
Polypropolene fibres - 5 handfuls?
CF board, 40" x 40" x 1" thick
Firebricks 230mmx114mmx76mm = 40

(superwool insulation, vermiculite layer and render I have separately)

Can anyone who's built the same or with experience please give this a quick once over to ensure I am not completely off the mark and actually ordering a stupid amount of material!

I don't know when the build will start as the forecast is ridiculous for rain up here for the next week or so, but does anyone have any sort of timeline for building on the vermiculite slab? Its been 3 days now, is 2-3 weeks about the norm for curing?

Thanks again, cheers.

Dave

[david s]

david s I went with around 63 % high for my door opening but looking at it now I think I may have gone a little too wide. Have you even seen or do you think it's possible to make a sort of half door that would shut the mouth down to retain more heat while at the same time still being able to operate the oven?

A sort of door on stilts at the sides, so you could slide the peel under it.

Maybe wait until you've built and fired it, see how it goes, then start tinkering.

[Daveholdn]

Thanks again david s, I'll mess around with the gallery forms and see what looks and feels right.

[Hattori-Hanzo]

david s I went with around 63 % high for my door opening but looking at it now I think I may have gone a little too wide. Have you even seen or do you think it's possible to make a sort of half door that would shut the mouth down to retain more heat while at the same time still being able to operate the oven?

A sort of door on stilts at the sides, so you could slide the peel under it.

[david s]

Hi Dave,
I usually wait 48 hrs. Because the stuff is pretty crumbly sometimes the formwork will pull some of it away, but it’s easy enough to repair. Hope you oiled your formwork.
The 63% rule is really not as important as most have you to believe. The larger the mouth the greater the heat loss. Conversely the smaller the oven mouth the more difficult it is to work the oven. So it’s like boat hull design V , flat bottom or a compromise between the two, totally your choice.

Dave

[Daveholdn]

Thanks david s, I've ordered a load of sand and a bit more just in case as I heard it takes a bit more than you think!

I poured/crumbled my vermiculite slab layer today, 5:1, weird stuff to work with but seems all good, I know it takes a while to cure but with reference to taking the form/shutter sides off, how long should these be left on, and at what point has anyone started building on the slab? I've read quite a bit and understand it's a waiting game now for the slab to get rid as much water as possible, and can take up to 3 weeks?

Also, I'm getting to my flue gallery and oven entrance, I'm going to set the flue back as far as possible to make the gallery as short as possible, but for the entrance for the oven itself, I understand height is most efficient at 62% of the internal oven height, but is there any such rules for the width of the oven entrance?

Thanks and any info is really appreciated.

Cheers Dave

[david s]

Any sand should do, but builders sand is probably the best as it is graded, ie it has a range of grain size which apparently results in a stronger bond between cementious materials (cement, lime) and aggregate (clay and sand). The high clay content and lime give the mix great workability so some larger sand grain size doesn’t matter. Make sure you wear rubber gloves as handling the stuff for more than about 15 mins will damage your skin.

[Daveholdn]

Thanks david s, I take it any builders sand is good to shape, you don't have to buy like a fine plasterers sand or anything like that? and Chach thanks also, only reason I was concerned was for strength of paving slabs but I've been assured because of the middle supporting leg, the slabs will be fine.
I'm going to lay my vermiculite 5:1 slab this weekend, I have a form measured out but has anyone had any experience of framing a vermiculite slab with bricks? I have a lot of bricks in the garden and thought I could lay and mortar a border of bricks on their side (4" tall border) which would act as a form for the slab. Would the slab be too much for the bricks and just simply force them off?

Thanks again,

Dave

[Chach]

Glad you stumbled across this great forum. This is where you want to be when your building your oven as there is a plethora of information here. If your not happy with your paver "slab" Now is the time to think about a reinforced concrete slab for your insulation and oven to sit on. If your not happy with the way things are going my opinion is to stop think about it and fix or change it right then and there before it's too late and you regret it. Never settle because you probably won't be happy. You're going to do a great job so congrats on your start.

Ricky