Using different size arch bricks to build the dome?

[Wheels1974]

I just found out that I can purchase two different size arch fire bricks at no extra cost. These arch fire bricks come in two measurements approximately
3"/2.5"x4.5"x9" and the other one measures 3"/2"x4.5"x9" although for what it's worth because we use metric here in Australia I will write down the exact sizes of these two arch fire bricks and the standard fire brick in millimeters.
The arch bricks are 230x115x75/63 and 230x115x75/51
The standard fire bricks here are 230x115x75.

I believe they could work well when building the dome as well as just the arch because it should save cutting and should also fit better and save on extra mortar. Has anyone here used these arch bricks to build there dome? Also do you think this will make building the dome easier?

Cheers

[Johnny the oven man]

Re: Using different size arch bricks to build the dome?

We sell 3 sizes, 75/69, 75/63, 75/51. Also have info on exact numbers of each for a specific arch size. Feel free to call on 03 9878 8884 John

[Keijo]

Re: Using different size arch bricks to build the dome?

Hey wheels guy,
Is 1974 your vintage or your car's?

I am in the process of building a dome right now using the 75/63 tapered bricks.
My dome diameter is around 900mm internal.

They work well.

The 75 to 63 taper does undeed make the dome build easier as it reduces the mortar join required, you still need to cut the bricks however.
But even with these bricks the mortar is still tapered somewhat as the natural arc of these bricks is too large for my oven size..

The 75/51 is too tight and would need the joins to be splayed out on the inside. Definitely no go!

Maybe you could get it pretty spot on by alternating layers of 75/51 and 75/63 and end up with very tight joints. You could try it out with a dry layout on one arc only.

In any case, the 75/63 work well.
When you think about it, there's not too many straight lines in a dome, so why would you use square bricks.

Here's a couple of shots of the tapered bricks in the process of going in.

Cheers,
Keijo

[nissanneill]

Re: Using different size arch bricks to build the dome?

Hi Wheels1974
and welcome aboard, yet another Aussie getting into the ovens.
James is missing out on a host of potential sales with all these new members coming on board from 'Down Under'.
It looks like you have things underway and being looked after. I will follow your build and be sitting on the side should you have any questions.

Keijo
looks like you have your mate looking over you. He''l be ready for the crust scraps once you get the oven going, which should be around Christmas, the way that you're progressing.
Great job.

Neill

[Wheels1974]

Re: Using different size arch bricks to build the dome?

Hey wheels guy,
Is 1974 your vintage or your car's?

I am in the process of building a dome right now using the 75/63 tapered bricks.
My dome diameter is around 900mm internal.

They work well.

The 75 to 63 taper does undeed make the dome build easier as it reduces the mortar join required, you still need to cut the bricks however.
But even with these bricks the mortar is still tapered somewhat as the natural arc of these bricks is too large for my oven size..

The 75/51 is too tight and would need the joins to be splayed out on the inside. Definitely no go!

Maybe you could get it pretty spot on by alternating layers of 75/51 and 75/63 and end up with very tight joints. You could try it out with a dry layout on one arc only.

In any case, the 75/63 work well.
When you think about it, there's not too many straight lines in a dome, so why would you use square bricks.

Here's a couple of shots of the tapered bricks in the process of going in.

Cheers,
Keijo

Keijo,
Nah mate "74" was the year I was born and I use "Wheels" as a nickname because I'm in a Wheelchair. Although I often get asked what 1974 vehicle I drive. lol

Thanks a TON for your reply, its much appreciated mate. You wouldn't happen to live in Melbourne Australia would you?
My father is building my wood oven for me and we have played around with the fire bricks in order to see what works the best and after viewing your photo's we have decided to do the first row of bricks like you have done, with the brick standing up. It seemed like the best way to go while we laid them on the floor last week but we weren't 100% sure, but now after seeing your awesome photo's that is now CONFIRMED so thank you.

I have a question regarding the top two or central two middle bricks on your front arch, are they a 75/63 brick just cut in half which will make those two bricks approximately 4.5 inches or 114mm?

Also one last thing which is our main concern, is the support of the arch as its basically supporting itself apart from each brick being mortared together either side and at the back of each brick. We were thinking about using some steel for added support for the arch's but the people who sell us all the stuff for the wood oven suggested it would NOT be wise using any steel because of the way steel expands and contracts especially when heated.
Basically what I'm asking is as we all know mortar will always crack in places. By having each brick mortared is that enough support for the arch's to stay upright without any problems?

P.s. I noticed you have used two kinds of refectory mortar when joining your fire bricks. When I read the Pompeii instructions I read that they suggest the front of the bricks touch without using mortar. I am using a similar method to you I think which is great to see someone do the same. Here in Melbourne my supplier told us to use a 1mm to 5mm refectory mortar where the tips of each fire brick touch and then use a 5mm plus refectory mortar for the rest of the back fill.

Hope to hear from you soon and thanks allot for your reply and great photo's
Cheers

[Keijo]

Re: Using different size arch bricks to build the dome?

Hello Wheels,

If you look at my post heading you will see that I live in Jamberoo NSW.
That?s on the East coast of NSW, quite a large town now with a population of just over 1,000.

Regarding the two central bricks:

The problem with all arches is, that no matter how carefully you make the template and no matter how carefully you lay your bricks, there will always be some error when you arrive at the apex.

So the two central bricks are not any standard. They are custom made from a square brick so that the joints will match the joints around them.
I think in my case they ended up being about 85/66 each.
I?m no bricklayer but even the experts seem to need to custom cut the keystone or the two keystones in my case..
So subsequently they are 75mm wide, which leaves around 155 for the length of the flue hole.
I agree with not using the steel support for the reasons you were given although others here use steel with no problems. I just don't think it's needed..
Arches by their very nature are inherently strong and you will have no problem at all in them being self supporting.
If you use a good quality mortar you won?t get any really bad cracking. Maybe some visible fractures but the bond will still be in place.
You will notice that in my case the door arch and the flue arch are bonded together and help support each other, for even more strength.

With regard to the mortar:
Again I agree with your supplier?s advice. Although there may be cheaper options, I don?t think there are any better.

I have also used two kinds of mortar.
The first is a very fine adhesive from Shinagawa refractories called Shirabond 50
This is a very high strength air cure adhesive mortar, which I use to initially bond the bricks in place. It dries to quite a high strength but will need full operating temp?s to fully set. It is not suitable for gaps much beyond 5 or 6 mm.

I then filled the larger gaps using a casting mix, called shiracast (I think). It?s a full blown castable refractory. You could make an oven just out of it. That?s the lighter color stuff.

Here?s a couple of more photos of how the very fine mortar makes for a tidy job.

I did sponge the face of each brick clean as I progressed to keep the job looking neat.
You will notice that when I laid the initial soldier course, I didn?t have the floor covered. This allowed me to keep the floor to dome join very clean as I progressed. I then covered the floor to keep it clean as the dome was built

Notice also that when I did the flue arch, my template included the outside of the bricks as well.
I added this because I had noticed that during the first arch, the door arch, although I was able to stick to the template on the inside curve, the outside and the angle tended to drift out as there was no guide for that. As I daid I'm no bricklayer and this is my first go at it, so I need all the help I can muster.

Anyway, I?m now feeling like Ernest Hemingway so I better stop here.

Good luck with your build guys,
Cheers,
Keijo

[Wheels1974]

Re: Using different size arch bricks to build the dome?

Keijo,
Firstly thanks again for all your advice and photo's, it does help big time.
I would like to pick your brains a little more, hope you don't mind mate. I'm curious to know what your thoughts are for the standard concrete foundation where the fire will be cooking not the ground foundation, also the insulated refractory cement whether it be Vermiculite, or Perlite or something like Sherlite and lastly the insulated 20mm or 25mm or 1inch board.

My father and I have already done the foundation which is just standard concrete and obviously rio for structural support. This is 100mm thick or 4 inches.
We are now thinking of either making more standard concrete around 50mm to 75mm thick to raise the height and then either putting a 25mm or 50mm layer of refractory cement. Then lay the 20mm insulated board on top prior to laying the fire brick which will obviously end up the oven floor where we do all the cooking. Or would it be better to just stick with the extra refractory cement and go 100mm using just the refractory cement (SHERLITE) I think its called, works the same as Vermiculite, if not better because its specially made for this purpose. We already have the 20mm insulated board so I figure we may as well use that also regardless of what we do.
I guess its fair to say you can NEVER have enough insulation.
It's the added insulation that keeps each individual wood oven hotter for a longer time and more importantly it should sustains a even temperature for longer which is very important IF you ever want to use the wood oven for cooking roasts and the likes.

What have you done or do you have any advice regarding any of the methods I suggested?

Regards
Wheels1974

[dmun]

Re: Using different size arch bricks to build the dome?

My take on insulating castable refractory products is that they are not worth the cost. You pay a huge premium over vermiculite/perlite concrete and don't get any real advantages at the temperatures we work at.

[Keijo]

Re: Using different size arch bricks to build the dome?

Hi Wheels,

I'm not really an expert on this topic, and I don't know the prices or the insulating ratings of each of the products, so the full answer is best left to someone else.

However, I did consult the experts at a local refractory supplier here in the Illawarra.
The company specializes in industrial installations but do have retail sales and in fact sell and install pizza oven kits of the castable variety. They have also installed fully bricked versions.

They told me that Vermiculite board, around 1" thick, under the floor pavers would me more than enough insulation for the application. Anything more would be paying money for nothing.

This is what I installed, but on top of a 1" thick high density hardieboard which I had lying around and wanted to put to good use. It also has some good insulating qualities as well as helping to provide a perfectly flat starting point.
The whole lot sits on compacted quarry dust, which effectively ends up like a block of concrete and has no compreession over time.

True enough that you can't have too much insulation from the insulation viewpoint, but as dmun above says, you can end up paying a lot for very little further gain.

Going with the vermiculite board is a good idea because the laying of the floor bricks is very critical as you don't want any protruding edges at all.
This process will now be easy as you have the perfectly level base to lay your bricks on.

I was able to get the floor as damn near perfect as possible by coosing bricks of matched thickness for that area. The bricks do have some manufacturing thickness variation tolerance ( something slightly less than 1mm), so it pays to go through this process.

Cheers

[Wheels1974]

Re: Using different size arch bricks to build the dome?

My take on insulating castable refractory products is that they are not worth the cost. You pay a huge premium over vermiculite/perlite concrete and don't get any real advantages at the temperatures we work at.

Dmun,
For a 1 meter (or 40 inch) outside dimension wood oven. The costs to have it covered with a 100mm or 4 inch thick layer of Vermiculite or Refractory product such as SHERLITE here in Australia.

The cost to use Vermiculite and what we call a cement fondue which is needed to mix with the Vermiculite would cost between $240 and $260 (Australian Dollars)
(Normal cement can be used but it does not work the same as the Fondue. Cost wise, there is very little difference between normal cement or the Fondue)

To use SHERLITE which is a refractory product will cost between $200 and $220 (Australian Dollars) So for whatever reason the Refractory products here in Australia are cheaper.

One of the advantages when using a Refractory product is that its new technology and was made for the intended purpose that we are using it for as opposed to Vermiculite or Perlite.
Admittedly like "DMUN" mentioned and the place I purchase my stuff from suggested, even though its new technology there is not a MASSIVE difference between the Vermiculite or the Refractory product providing you mix the Vermiculite with the Fondue, However if you chose to mix the Vermiculite with standard cement then there are marked difference between the two products when used as a insulation for wood ovens.
The GREAT advantage the Refractory product has over the Vermiculite is that it is extremely easy to work with as opposed to Vermiculite, all you need to do is add water to the Refractory product and your done. It is exactly like working with cement. I just want to mention we have NEVER worked with Vermiculite and I am just going by what I have heard from many people who have used Vermiculite, I have also seen it being mixed and used via the Internet on a video watching someone use it on there wood oven and it did look very coarse and the consistency looked kind of dry.

I purchase a great deal of stuff from the USA simply because most things from the USA are at least half the price then here especially now with the USA dollar declining. Although I have always found most things in the USA cheaper even when the USD was strong and that's obviously due to the population difference between our two countries. I am shocked to know that in this particular case Vermiculite is cheaper then Refractory products in the USA.
Either that or the price of Vermiculite here in Australia is through the roof which wouldn't surprise me at ALL. lol

Regards
Wheels1974