just about to start a build

[al fresco mark]

Hi,
I am just about to start a build, I plan to cast a dome about 24 inch round 15 inch high , I am thinking of using a mix of fondu cement (alumina cement) and vermiculite , a mix of 1 to 4 by volume, I am thinking a thickness of 3 inch with a chicken mesh reinforcing . The floor slab I intend to use the same material and the same thickness with a re-bar reinforcing.
Don't yet know how I'm going to water proof the dome and would love some feed back on this, and, if the way I am thinking of building the oven would work well or needs to be modified and or improved in any way.
As yet I have not bought the materials but will be putting in an order soon as I also use the same materials when I build my blacksmiths forges, as the cost is not insignificant I really don't want to over order so you feed back could save me a chunk of money

[james]

Re: just about to start a build

Hi guys,

I moved this to Other Oven Types. I think it will get a better response here.
James

[GianniFocaccia]

Re: just about to start a build

Sounds like a neat project. Just curious, though - What effect does the vermiculite have in the dome material and it's effectiveness in retaining and radiating heat?

[dmun]

Re: just about to start a build

You understand that a brick oven is quite different than a forge or a kiln: a dense inner layer absorbs and radiates heat, and an outer insulation layer keeps the heat concentrated. There are different ways of doing this, but the theory remains the same. Any attempt at doing a "one layer" dome is bound to be problematic.

A final note: refractory concrete is chalky, and if mixed with a light weight aggregate like vermiculite, it will be flaky as well. You may want to consider a firebrick floor, as your food will be cooking directly on it, regardless of what your dome is made of.

Have you seen our plans? Studying them will be helpful no matter what approach you finally take.

[david s]

Re: just about to start a build

Don't use vermiculite as your aggregate. You need a dense material that will give you thermal mass. Vermiculite won't do this and will reduce the domes ability to conduct heat right through resulting in a slow time to heat soak the material. You would be better off getting a mix already made up that contains the correct dense aggregate in the correct proportions as well as fly ash and fires to prevent explosion etc. etc. Making up your own brew may be a little cheaper, but you are bound to get something wrong. Go to a refractory supplier and get them to advise you on what product to use, there are lots of them, dense, insulating high duty low duty etc. etc.
Dave

[david s]

Re: just about to start a build

"fly ash and fires " should read fly ash and fibres, sorry

[al fresco mark]

Re: just about to start a build

Thanks Dave,
I have managed to find a bit of time to navigate around the FB site and now have a better understanding of what is required , a big thanks for putting me right with this first part , no doubt I will be posting more questions as I go through this steep learning curve.
I have plenty of fire clay so am thinking of using that up and then use the vermiculite/cement mix on top of this as the insulation layer

[al fresco mark]

Re: just about to start a build

Many thanks, will do a lot more research before I start, love the geodesic project, its got me thinking !

[al fresco mark]

Re: just about to start a build

Thanks to everyone who has given me added information,
I think it would be a good time for me to add a little bit of background info here ,
The main reason for the wood burning oven build is that this summer I want to start some week long courses in primitive metalwork and green woodworking , these courses being a week long mean that we have also to consider feeding and what better than a wood fired oven !
I started to look into this and soon found this site and I am very glad I did !
already I have saved time and money by being directed away from the wrong course of events,
I have now done a little more reading and am starting to get my head around the difference between an oven and the furnaces / forges I have previously built,
When I mentioned to friends and family about this project I had immediate orders for 3 of the ovens so I thought that it might be a good idea to make a mould that I could use for a few more times,
I will get my act together in the morning and start to photograph the steps for all to see,
I have purchased a couple of beach balls from e-bay ( be careful of the way they measure the ball , a bit of skullduggery in making the product seem far larger than actual, measuring half the circumference and not the normal diameter )
The ball was then used as a mould for the dome , I covered it with cling film then a layer of wall plaster , I managed to get rid of some "past sell-by date" stuff that once no good as a building product worked fine for this project ( plaster when old tends to go off very fast when mixed , no good for building but if you mix up only small quantities at a time is great for putting a hard skin over the beach ball,
I made the door opening out of a couple of old boxes and will cover the whole thing with another layer of the plaster,
The next part of my plan is to cover this plaster layer with fiberglass and then use this as the mould , not having any fiberglass resin or matting it was time to pop down to my local , fortunately the pub in question is one of those places where you can source just about anything and sure enough an old friend said he will supply the nesassary goods by Tuesday night,
I will get the photos sorted tomorrow and then keep an up to date portfolio going from then on , I hope this might be of interest to you all but I guess more so for the ones like myself who are new and on the learning curve for this type of project

[al fresco mark]

Re: just about to start a build

/Users/macuser/Pictures/iPhoto Library/Originals/2008/4 Sep 2008/P1010099.JPG

this is the project so far, unfortunately I don't have any photos of the stages before this , when I deconstruct the dome I will photo the relevant parts and post them.
What I am now thinking is to make a fiberglass mould then cast onto this a 2 inch layer of fireclay mix ( not exactly sure as to the mix yet but would welcome suggestions ) then over the top of this another inch of cement /vermiculite mix.
For the base I have found some large fire brick at the back of the workshop ( photos to follow) and thought I would use these on top of a couple of inch of the cement/vermiculite mix.
Would love feed back as if to now I am going down a better path then my first posting

[GianniFocaccia]

Re: just about to start a build

This plan sounds more salient. The insulation layers below and above the oven are critical to it's efficiency. Four inches of vermicrete below your firebrick floor will prove more effective than two inches. Since you will be casting your dome, you may want to take a look at what others did in the builds labeled 'Other Oven Types' on this site.

[JoeyVelderrain]

Re: just about to start a build

I can't see your pictures Al. the link is messed up.

[al fresco mark]

Re: just about to start a build

Thanks for the info , sounds like I am now on the right track , sorry about the pictures not being there dont know what I did wrong , somehow got it into the main picture gallery and not on this thread , will try and sort this out soon,
Many thanks.
Mark

[al fresco mark]

Re: just about to start a build

Well a couple of weeks on and a lot more reading done on the forum, I now realize that I need to re think this build , I am going away for the next week and will get my head around the way I now want this build to go and will post some questions on my return , I still cant manage to find out how to post pictures on the thread so if someone could direct me on this issue then I will post some pictures, I still plan to make a mould so that I can make 3 ovens and have some ideas for this and the photos are waiting, more in a weeks time, many thanks ,
Mark

[dmun]

Re: just about to start a build

Photos:
Click "go advanced" under the message box. On the page that comes up, click "manage attachments". A little box pops up; click "browse". Choose your picture file location, then click " upload". Lather, rinse, repeat, up to, what, five times? Don't forget to go back to the original message and click "submit reply"