FB Materials List

[DaveHI]

High School Geometry Method

For my 36 in. Dia (inside dimension) project in the making.

1) Floor

a) Inside the dome Area = pi X R^2 = 1017 in2 (pi = 3.1415...)

Fire Brick 4.25 X 9 = 38.5 in2 so 26 bricks
Obviously low as many cuts so
assume 36 X 36 square or 4 bricks X 9 bricks or 36 bricks.

I'll assume 35 for my project and press on.

b) Dome on Floor design 45 X 45 inch square
or 5 bricks X 10-11 (ish) 50-55 bricks
if you assume a 45 in dia circle you get 42
In the real world you probably need about 50

2) Dome -- Inside Area = 2 X pi X R^2 (half a sphere)

If R = 18 in Area = 2035 in2
Deduct 18 X 12 opening 216 in2
Net 1820 in2

If you make this out of 2.5 X 4.25 blocks (10.6 in2) you need 171 halfs or
86 whole bricks
since my dome extends 2.5 inches below the floor I need more surface area totaling about 13 more.
So call it 100

Entry arch -- 25? (eyeball guess looking at that awesome effort on the "no form" oven.

Total -- Floor 35
Dome 100
Arch 25
Total 160

Multiply that by finagle's constant and order away. Matches the 175 count within my comfort level so at least I feel confident in ordering about 200 whole bricks. With freight to HI, I'm looking at $3/each even with me picking them up at the freight yard so overkill on the count gets to be pretty good beer money in a hurry.

[Hendo]

Re: FB Materials List

David,

The tapered (ie arch) bricks I?m getting are about the same price as normal firebricks for some strange reason. Another oddity is that the tapered bricks I?ve ordered are imported from Europe, and are cheaper than those produced locally! The only downside (if indeed it is a downside) is that they are medium duty at 40% alumina, compared with 23% alumina for the local variety. I don?t think this will be a problem for the dome, which is the only place I plan to use tapered bricks.

Because of the height of the thermowells (now cast in position in the hearth slab), I have a choice for the floor of 2 layers of 230mm x 230mm x 38mm (9? x 9? x 1??) tiles @ 23% alumina content, or standard size bricks laid on the (3?) flat, either 23% alumina or 40% alumina. My supplier doesn?t think there will be any problems with the medium duty firebricks on the floor, even for baking bread.

Thanks for the clarification of firebrick size ? I didn?t know this until now. Another reason for including brick sizes on the Materials List!

Cheers, Paul.

[carioca]

Re: FB Materials List

Hendo, did you get those firebricks from Darleys, at Bacchus Marsh, Victoria? This is where I got my tapered bricks in two different tapers, 35 of one and 65 of another (for details pls see Picasa Web Albums - carioca - Forno_del_gallo ) - and they never claimed these were imported!

In any case, even allowing for the fact that all except the bottom ring bricks are supposed to be cut in half, the total number of bricks for my 39in/1m internal diameter oven is around 100!

And i seem to be cutting corners, too (pun intended) on the stand: my hexagon-spokes stand used 48 rpt 48 concrete blocks! (I am neglecting the fact that a proportion were actually half-size blocks, 2 of which I simply counted as one...) Again, see the Forno del gallo link...

At least YOU don't have the problem of WHICH type of tapered firebrick to start with, and how many layers of each type :-)

Cheers,

Carioca

[Hendo]

Re: FB Materials List

Carioca,

I had two choices of tapered bricks ? the Victorian ones or imported. For a number of reasons, I elected to go with the imported ones.

As recommended by both Maver and me (in a private message), it seems logical to start your dome with the bricks having the greatest taper, and continue with those with lesser taper.

As part of my current dilemma, I developed a hypothetical model for estimating dome brick quantities, and applying it to your kit for a 1000mm (39?) internal diameter dome, I found the following (see assumptions below):

1. the first three rings made from 75/57mm (3?/2??) tapered bricks require 72 half bricks, or 36 whole bricks. This equates closely to the number of bricks in the kit (33).
2. the remaining five rings using 75/63mm (3?/2??) tapered bricks require 98 half bricks, or 49 whole bricks. This is 18 whole bricks less than contained in the kit (67).

Assumptions:

1. each whole brick, when cut in half, is 110mm in length (they will probably be marginally more than this, resulting in fewer bricks being needed).
2. the oven opening will ?replace? four bricks in each of the first three rings. This creates an opening of around 450mm or so. If you are planning a wider opening, again fewer bricks will be needed.
3. the oven opening will affect only three rings of tapered bricks, as the first ring is recommended to be of standard bricks, laid flat (but see alternative suggestion for the first ring below). The height of the opening will therefore be four rings high, which is pretty standard from what I?ve seen.
4. No allowance has been made for bricks required for the vent or oven opening.
5. Note: my model gets a wee bit rubbery for the two uppermost rings, and there is no way of knowing whether more or less bricks will be needed due to the cutting that will inevitably be required, particularly for the top ring or ?cap?.

OK ? what to do with the excess of eighteen 75/63mm (3?/2??) tapered bricks? I have an idea. 43 half bricks (or 21? whole bricks) could be used for a half-height soldier course as the first ring. If the dome encircles the floor tiles, instead of being placed directly on top of them, the net effect of this would be a first ring height of 75mm (3?) assuming 38mm (1??) floor tiles are used. I know that there is a small shortfall here, and you have ended up with 50mm (2?) thick floor tiles, but I wonder if the kit was designed using these assumptions (ie half soldier course of tapered 75/63mm bricks around 38mm floor tiles inside the dome)?

This appeals to me, as the figures all tend to tie up ? well, within a few bricks, anyhow. The straight bricks you?ve got could be used for the oven opening and vent, or cutting a few more tapered bricks if you do end up with a shortfall.

Gee, puzzles are fun! I can?t help but reiterate though, that my model, while seeming to be broadly consistent with the experience of other members is completely untested. The only cross checking I?ve done is to determine numbers for my first (1100mm) ring using dividers on a scale diagram which gives 26? half bricks, versus 27 from my model.

Let me know what you think.

Cheers, Paul.

[carioca]

Re: FB Materials List

Thanks for the very detailed and helpful information, Hendo!

Yes, Maver had suggested starting with the steeper taper also to me (a suggestion I initially rejected out of hand but later came back to as part of my own efforts at solving the puzzle!).

Indeed, my preferred solution at the moment is this: starting with three rings of the steeper tapered bricks, then nine rings of the flatter ones.

The Darley people told me specifically - although they did not rpt not have the benefit of having 'inherited' any instructions for their 'kit' from the retired foreman who developed it! - that the first ring should consist of whole bricks, while for all subsequent courses the bricks should be cut in half.

Because I have the extra 20 flat bricks I ordered with the 'kit', and because my floor tiles are 50mm high, I have considered using the whole flat bricks as the first course and then starting with the steeper tapered ones.

I also will keep the floor tiles entirely WITHIN the first circle of whole bricks, i.e. cutting them to fit the surrounding firebricks.

But no doubt I will have lots of fun still laying up various models of dry-laid (without mortar) firebricks in all kinds of arrangements until I come up with the most stable and most simple layout... here your calculations will prove a great help!

I'll keep you posted. At present I haven't even formed up for the hearth yet. With my unusual design this should prove another challenge... But I've bought some 6mm fibre cement boards to use as 'lost' formwork under the hearth, and will use old sheets of very thin plywood to get the outer curve right!

Cheers meanwhile, and thanks again for your help!

Carioca

NB: A man in Victoria who built with normal firebricks made the point that the height of the opening should be exactly 60 per cent of the height of the dome. I will check what the FB forum recommends, but meanwhile if this is something that your model also calculates, pls let me know, ta.

[RTflorida]

Re: FB Materials List

James, newbie here, I am at the stage of pouring my hearlth slabs. to this point the materials list has been very helpfull. This an amazing source of info and materials .was a bit disappointed that my orders for 5 bags of refrax are on a boat coming from Italy. (backorder - late April) what is my best choice - a no name refracory mortar from 2 local suppliers OR should I give the 1-3-1-1 recipe a try. Really wanted the Refrax, but can't wait. So what is my best alternative?
Thanks - Randy - RTflorida

[james]

Re: FB Materials List

Hey Randy,
Sorry we ran out of Refrax. We've upped our order with our next container (though that doesn't help you).

If cost is less of an issue, you should look for HeatStop50. That is a 50lb bag of dry, premixed refractory mortar made in the states. It is more heat resistent than the 1-3-1-1 Portland cement mix. I have never used it myself, but I know that other builders have.

Let us know if you find it.
James