So ... after months of planning and reading i have finally started construction of my oven!!
Firstly thankyou to every one who has helped so far and hopefully a few will follow this build and chip in along the way with suggestions and tips and answer questions i'll no doubt have!!
ok so the build is a 32" pompeii oven made mostly out of reclaimed materials i have managed to source through work and off friends, who i must note are probably sick to the back teeth of listening to me go on about the oven all the time!
the dome its self is going to be constructed of solid clay reds on a storage heater firebrick hearth built with a lime mortar mix and insulated with vermicrete then rockwool then more vermicrete and a stucco igloo finish.
ok i'll pop some pictures up of where i'm up to and see what you guys think!!
a couple more pictures. i was going to pour the vermicrete under the hearth tonight but had an idea i wanted to run by people first!
i have got some kingspan (poly urathane) insulation from work and wondered if i could put that in first then a layer of 1 1/2 inch vermicrete on top to bring me up to brick level? i know its got good compressive strength and very good thermal insulation, not too sure about temps though or what sort of temps it would even be getting to down there under the bricks and vermicrete? what does anyone think?
also i have 2 100 litre bags of vermiculite will this be enought to do under my hearth? area is 50" by 62" and just under 4" depth. is 6 to 1 mix ok for this slab?
Used some to block up my doorway whilst using a 500w Halogen lamp as a heat source for drying out my oven. The Celotex buckled and showed signs of heat damage (swelling, foil coming loose and discolouration of the foam) when i was reading about 100c constant temp.
Its a brilliant insulation, but not for a WFO in my opinion...sorry.
You'd need far more Vermicrete to ensure that the Kingspan kept cool enough, so why not splash 15-20 quid on some Thermolites?
I have toyed with the idea of of putting 1" kingspan as a base for an oven on a trailer....then 4" of thermolite blocks. I would say that you need a minimum of 3" of vermecrete/insulation block to protect the kingspan. I know it has enough strength....but it must be protected from direct heat. (if you put a naked flame on kingspan..it catches alight).
It may work....and add some thermal value, but I'm of the same opinion as Danno...... forget the kingspan and lay 4" of vermecrete....or a layer of insulation block on flat.
A 100 litre bag of vermiculite is equal to .1m3....or 1m x 1m x 10cm....or 36" x 36" x 4". To calculate your area of 50" x 62" x 4"...it's easier to convert it to metric...127cm x 158cm x 10cm = .2m3....or 200 litres (2 bags).
The standard method of insulation over the dome is the opposite as what you propose...we normally lay thermal insulation blanket (minimum 2")..then vermecrete (minimum 3") (between 3 and 4 bags for a 36" Pompeii).
Dont forget to double up on the thickness of your brick and insulation layers (4 1/2" brick, 2" blanket, 3" vermecrete..x2) when calculating how wide the internal diameter of the oven can be. You may be a little shy on the width of your slab for a 36" internal hearth.....please double check your measurements.
i decided not to use the kingspan in the end (as you both say good insulation just not for our purpose) and went for full vermicrete it used just short of 3 bags. in hindsight i wish i had used thermalites but i'd already bought the vermi so went with it!
my base size i have to work on is 1500 by 1800mm and i'm planning the finished oven to be 800mm internal or 32" i think this should be fine for my needs or do you think its a bit on the small size? i could probably push it up to a 34" without any problems?
i am thinking about dropping the vermicrete from around the dome as i think its going to be hard to work with and instead just using 4 to 6 inch of rockwool what do you think? i emailed the makers and the said it was good to 680 degrees constant working temp so i dont think i'll have any issues there? i think danno used it but ontop of a layer of Ceramic blanket. what do you think?
next step iws get some templates cut out for the hearth and internal arch and i can get started cutting bricks etc!
how long should i stay of the vermi i have put in today before starting putting the floor down and building the dome i am eager to get going!!
Keith, i used Rockwool fire blanket. A different product to normal mineral wool, and it can withstand higher temps. I only used it because of the ceramic blanket i had. Rockwool is very soft, so you'd be creating a new issue by thinking you can forego the Vermicrete. You'll struggle to get a solid enough foundation for render. Unless your building an enclosure, but then the loose fill quality of vermiculite is better again.
danno, what size is your opening? just re read your build thread but not sure if it says? also your oven is a 36" right? i'm going to have a measure up i think and see if i can fit a 36" on the space i have! i'm concerned now that 16" isn't a wide enough opening but i'm worried that if i push it to 18" opening on a 32" oven i will lose too much heat from it?
I wish I could chirp in and give you a maximum % opening of the diameter of your oven....but I'm still searching for that magic formula.
Without finding a solid answer, I have looked on various wood-fired oven forums in France, Germany and America that I follow and sometimes post in to find this formula. What I have found is that people push their opening widths to the same % as internal arch height to dome height...i.e......63%.
If this is the case then a 32" internal diamater oven can have an opening up to 20" wide. This is just research and theory on my part and in all honesty I wouldn't go no more than 18"....when asked for advice on a maximum width for a 32" oven I would suggest 16"......as I know in reality that this works well.
I know that once the oven has some heat in it.....it starts working it's magic by drawing in fresh air from the base of the opening. the air then expands and when spent is taken over the dome and searches for an exit. The 63% rule of internal arch opening to dome height makes this air cycle work to give maximum efficiency to the oven dome....how the size of the opening relates to this process is still beyond me.
You must take into account that the larger the opening, the deeper into the hearth you will lose as the internal arch must be a part of the first ring of bricks.
.....as always, these are just my thoughts and contradictions are warmly invited!!!
p.s......kstronach....sometimes the forums get very busy and threads often get lost within multiple posts. If you get no response....but want one, simply reply with "BUMP" and this thread will bounce back to the top of "most recent topics"
p.p.s.....try and pick the bones out of my response......good luck.
Thanks, I am seriously considering upping the oven size to allow a wider door! I agree with you and don't want to go wider than 16" on a 32" build! I could definatly go to 34" and couldpprobably go to 36 at a squeeze. What do you think I suppose if I have the room I may aswell go bigger right? What width would you suggest for a 34" oven and 36" oven?
On my last build Corris Pompeii ...I pushed the opening to 18" on a 36" diameter oven. I've had some good feedback from the guys I built it for.
It looks like if you go any wider than 34" you may have to sacrifice some depth of your thermal layer over the dome, which is a no no.
The honest truth is....I don't really know. If you are set on an 18" opening.....go for it. As long as the oven has the correct insulation it shouldn't affect the performance or heat mass. The worse case scenario would be instead of maybe 3 small logs an hour to keep the fire flickering.....you may need 4?