Oven floor tiles - appropriate size

[BelgianBuilder]

Hi!

I'm building my own DIY dome shaped pizza oven.
This forum has a ton of information, which was already very helpful.

Nonetheless, some questions remain.

1. As regards the thickness of the floor tiles: I can get my hands on tiles with a thickness of 3cm/1,18 inch or 5 cm/1,97 inch.
I'll apply a perlite insulation of 11cm/4,3 inch. Internal dome diameter would be 82,6cm/32,5inch

The thinner ones are cheaper and probably easier to cut.

I want to use the oven primarily for pizza and if heating time can be reduced by using a somewhat thinner floor tile, that would be welcome.
The oven walls will be made of bricks cut in half, 10,6cm/4,17 inch wide. So perhaps the 2 inch tiles are necessary to balance the thickness of the dome wall?

2. As regards to the width of the tiles, I have to choose between square tiles of 30cm/11,8inch or 40cm/15,74inch. Is it always the better/easier option to go for the larger tile?

3. Can I bed the floor tiles in a mixture of refractory mortar, sand, cement and lime? Or is refractory mortar just fine? I can't find fire clay.

4. Different brands of refractory mortar vary a lot in price. For a 55lmbs bag prices range from 28 dollar to 60 dollar. What accounts for this huge price difference?

5. For an outdoor free standing oven, is it necessary to install a flu?

Thanks a lot for any kind of advice!

[rsandler]

Welcome to the forum! Others will probably chime in, but here's some quick answers:

1. 3cm tiles seem too thin to me; at that point I'd be worried that they wouldn't store enough heat for multiple pizzas. I'd go with the 5cm tiles.
2. Larger tiles mean fewer seams and less places to catch a pizza peel as you're trying to turn a pizza. So larger could be better. That said, many of us make our floors out of firebricks laid flat, which are much smaller than even the small tiles you have available, so either will work fine.
3. You don't want to mortar down your floor tiles at all--movement due to heating expansion will break the joints anyway. The recommended sand/clay mixture is just to help level. I did without in my first oven, and mostly did without on my second. With larger tiles instead of firebricks, it may be less necessary, though you'll want to be careful getting your perl-crete flat.
4. Can't help you on this one; I used the "homebrew" mix of sand-cement-lime-fireclay in a 3:1:1:1 mixture. You might ask about bagged clay from wherever you get your bricks and floor tiles--that sort of place often has some.
5. Even outdoors a flue keeps the smoke out of your face--you'll note most of the ovens on here are outdoors and almost all have flues. Doesn't need to be very tall, mind you.

Hope that helps--good luck on your project!

[david s]

Most oven builders opt for a 2" thick floor, but larger ovens often go for 3". If baking bread is the main objective some ovens even go for a 4" floor, usually by laying the floor bricks on edge.
The downside is that the thicker the floor the longer it takes to get to temperature and the more fuel that is consumed. 3cm is probably not thick enough and you will probably find that you need to recharge the floor after about 8 pizzas. This can be a pain and stops production for about 15 mins.


Also the larger the brick or refractory casting, the greater thye chance of cracks developing. This is one of the reasons why the floor bricks are laid loose. The larger the section the greater the difference in thermal expansion which creates stress and therefore greater propensity for cracking.

Can't help you on refractory mortar pricing, but as calcium aluminate based mortars are notorious for spoiling due to moisture absorbtion, the suppliers probably have to ditch fair quantities which would affect the prices they charge. Apart from price the very limited working time of refractory mortars makes them tricky to handle. This can be extended somewhat by using chilled water. Once calcium aluminate begins to set, it should be discarded. You can't rewet it like calcium silicate cement. Most builders here prefer the homebrew because of its more acceptable price as well as its far more user friendly nature. Its performance, at the service temperatures we use has not had adverse reports compared to the more expensive refractory mortars.There are also sodium silicate based mortars which use a different chemistry, but also have a limited working time. Follow the manufacturers recommendations for usage.

[BelgianBuilder]

Thanks a lot for these useful replies!

I'll go for the thicker but smaller tile to minimize risk of cracking.

I will cover an area somewhat bigger than the dome itself with the floor tiles, for aesthetic and practical reasons (easier to cut straight lines). It seems weird not to apply anything to bed the floor tiles down outside the perimeter of the dome, I suppose I could mortar down the tiles not covered by the dome and level the tiles inside the dome with plain sand?

[mongota]

Geting a flat floor:

I went through my stack of ~250 firebrick until I found enough of rough equal thickness bricks to use for the floor.

I then laid out the bricks I chose in a herringbone pattern, the pattern I chose for my floor. The pattern was dry set on nothing more than a flat sheet of plywood. I inspected the surface of the floor for irregularities in brick thickness. I moved one over there, tossed one out and replaced it, etc. Only took a few minutes. I ended up with a pretty flat cooking surface.

Once I installed my 4" of rigid CF board insulation on the slab, I transferred my floor bricks from the plywood to the insulation, their final resting place on top of the insulation.

I ended up with a nice flat floor. No leveling or bedding material needed.

After you oven is built, it you find a brick edge that constantly catches the peel, just hit that raised edge with an angle grinder to take it down. A quick swipe will do it.

Best, Mongo

[JRPizza]

Hey BelgianBuilder , I would not want to build an oven without a chimney, but if you do a search for bread ovens of Quebec (link below) you can see examples of rustic ovens and quite a few of them do not have any sort of chimney.

http://heatkit.com/docs/Bread%20Ovens%20of%20Quebec.pdf

[BelgianBuilder]

Thanks you all!

[BelgianBuilder]

Hi everyone!

Slow but steady, we're making progress here.

With a lot of help from this forum, we've made it thus far, but the inner arch is looming large at this point.

I sort of understand the basics of it, but there's one thing that confuses me.

On the full bricks forming the innner arch, you should have two cut lines. One cut line is determined by the inner diameter of the oven. But what determines the second cut line?

Option 1: second cut line is determined by the (estimated) heighth of the ring at which the course intersecting the arch sits. In our design, that creates a lip, so the TDC doesn't make full contact with the brick sitting on top. (see image nr. 1)

Option 2: second cut line is determined by de outer diameter of the dome (or the depth of the brick, in my case 4,13 inches). In that case the brick sits a little bit lower, thus creating a dip in the ring that probably has to be corrected for by shaving off a piece of brick before continuing the next course. (see image nr. 2)

What option is advisable from a construction standpoint? Or is it not that important and is either option fine?

Thanks a lot!

[david s]

Extending the floor tiles out beyond the outer perimeter of the inner dome is inviting heat loss via conduction. Generall it is better if the whole dome is encapsulated in insulation.If it were mine I'd be trimming off those floor bricks with a large 230mm angle grinder and diamond blade.

[BelgianBuilder]

Ok. Thanks for the advice, David. I will cut a piece out along the perimeter for the insulation to fit in.

Any idea on the positioning of the brick for the inner arc?

[NewEnglandNewb]

The best explanation of inner arch to dome transition I have seen is on page 4 of Mongo’s build.

https://community.fornobravo.com/for...ct-build/page4

[Toiletman]

Hi everyone!

Slow but steady, we're making progress here.

With a lot of help from this forum, we've made it thus far, but the inner arch is looming large at this point.

I sort of understand the basics of it, but there's one thing that confuses me.

On the full bricks forming the innner arch, you should have two cut lines. One cut line is determined by the inner diameter of the oven. But what determines the second cut line?

Option 1: second cut line is determined by the (estimated) heighth of the ring at which the course intersecting the arch sits. In our design, that creates a lip, so the TDC doesn't make full contact with the brick sitting on top. (see image nr. 1)

Option 2: second cut line is determined by de outer diameter of the dome (or the depth of the brick, in my case 4,13 inches). In that case the brick sits a little bit lower, thus creating a dip in the ring that probably has to be corrected for by shaving off a piece of brick before continuing the next course. (see image nr. 2)

What option is advisable from a construction standpoint? Or is it not that important and is either option fine?

Thanks a lot!

Good choice of beer :-D. Picked up a few cartons and the glass as well last time we visited the brewery/monastery. Do you live close to it?

You mentioned before that you couldn't find fireclay: I bought it from kachelmaterialenshop. Their shipping cost to Belgium and the Netherlands are pretty similar it seems. I might also have some left over once I'm done building the chimney (I live in Eindhoven), although it seems that in the end you went with a refractory mortar?

The arch bricks are indeed a little strange: in the end you'll always end up puzzling the rings going above it into place by shaving pieces off. There's also some pictures on how I did it in my build thread, post #24. In picture nr3 you see an IT additional tool that points out the external diameter of the dome. As everything else I've taken that IT additional tool design from one of the other threads, but I don't remember whose.

For the construction or the visual appeal I don't think anything really matters: it's all compressive loads and invisible.

[BelgianBuilder]

NewEnglandNewb Thanks a lot. It's cristal clear now how to figure out the inner and outer diameter. It remains a question whether one should take into account the heigth of the ring intersecting the inner arch, I guess it's not that important.

Toiletman Wow nice build! Impressive tapering! Did you get your other stuff (blanket, perlite) also from the kachelmaterialenshop? Indeed, I went with the mortar. As for the beer, the location of the oven is not that far from the brewery but It 's quite far from where I live. I like all trappist beers (the Dutch ones included ) but if there is one that stands out, it is Orval!

[nlinva]

I also puzzled about whether it makes sense to take into account the horizontal courses that abut the inner arch in cutting the arch bricks.

In the end I decided against it, feeling that 1) It should be a relatively straightforward cut to adjust the abutting horizontal brick to the arch (as opposed to vice versa), and 2) for structural strength, it is probably best to keep the arch bricks as straightforward as possible (i.e. the way it is explained in mongo's build).

[Toiletman]

Toiletman Wow nice build! Impressive tapering! Did you get your other stuff (blanket, perlite) also from the kachelmaterialenshop? Indeed, I went with the mortar. As for the beer, the location of the oven is not that far from the brewery but It 's quite far from where I live. I like all trappist beers (the Dutch ones included ) but if there is one that stands out, it is Orval!

Thx! Indeed, I also got the other materials from them in one order (fireblanket, fireclay, vermiculite, perlite, chimney, calciumsilicate and 'kachelkoord'). Only the stones came from broodoven and sand and cement and such from hornbach. Perlite and Vermiculite might be slightly cheaper from agricultural suppliers, but I didn't find any nearby, and with the shipping costs it made more sense to order everything at one place.

Fully agree on the beers