Newbie looking for advice

[Denis Li]

Hi All

i'm Denis and i'm from Mauritius (tropical island in the indian ocean, east off the coast of Africa). about a month ago i embarked on a pizza oven project and i would like some advice from you guys. i post a photo of the point i reached. it's a mock laying of the bricks for the hearth and part of one of the walls to get an idea of the oven. i'm aiming for a barrel vault type oven.

my first concern is whether the wall to which the concrete table is attached to will get damaged when the oven gets hot. there's a 10cm (4 inch) space between the oven's rear wall and the house wall. if i fill it with a perlite-cement mix, will it help insulate the oven and protect the wall? i suppose i need to put a layer of insulation between the hearth and the concrete table as well.

my second concern is how high should i go for the ceiling seeing the dimensions of the hearth? (inside space is 70cm x 60cm or 27.5" x 23.5")

i also realize i'm a bit short of space on that concrete table and i underestimated dimensions ... i suppose i'll be able to insulate the sides of the oven but not much near the front. here it is for now, your advice is greatly welcome and i hope things won't go wrong.

Regards
Denis

[SableSprings]

Re: Newbie looking for advice

Hi Denis! Welcome to the forum.

You definitely will want to insulate your oven from the back wall and the bottom concrete slab as well as over the top/sides. If you can't get the insulating board for the base or ceramic fiber blankets for the top & back, then the "old style" of perlite/cement will work just fine. Lots of information on the different ratios recommended for the old style insulation in the forum but it really is important to think as well about what kinds of things you are going to cook...just short term, hi-temp pizza or longer, lower temp items like breads and roasts. The bottom line for everything is that you really can't have too much insulation.

The oven's inside height dimension will be determined by the height of the door. Classic ratio of door height to oven dome is 57% -- more modern studies recommend that 63% is even better. So, by my math, if you look at making the opening about 11" (28 cm) tall, the inside height of the oven should be between 17.5"-19" (44-48 cm). I'd make the opening around 15" (38 cm) wide (to allow a half-sheet pan in/out).

Here's Lburou's great thread & links to some of the best information sources in the forum.
http://www.fornobravo.com/forum/f2/n...res-15133.html

[Denis Li]

Re: Newbie looking for advice

Hi Mike

Thanks for the welcome greeting. I'll try to download the pompeii oven plans (haven't succeeded so far, some kind of log in problem) for more information. The intended purpose of the oven would be to cook pizzas in and if i understood correctly, after proper insulation, i'll still be able to bake or roast after the fire dies down. so that would be a bonus.

Re. about the height of the dome, the part about the door height to dome height ratio is clear but i thought there also had to be a relation with the size of the cooking surface. i mean, i thought a small cooking surface would mean a lower dome but is that not true?

edit: i add 2 pictures of further mock brick laying. that's where i got to so far. I'm still trying to source perlite, so i have time to look at design

[SableSprings]

Re: Newbie looking for advice

I don't know of any restrictions of dome height based on cooking floor size. If you are going to cook mostly pizza, then having an adequate space for your fire and pizza is the primary concern. You generally want the lower dome for pizza to help cook the top a little faster (to keep up with the hearth cooking temp). I've seen several commercial barrel shape WFO systems that are almost 2 meters in circumference...and still maintain the same opening to dome height ratio. The door width is primarily a convenience issue. My oven is over a meter deep and 1 meter wide. I do both pizza and bread and find my 19" (40-45 cm) width door works well for me.

I think the access to the cooking surface and how big of a door you want are the major considerations to look at next. Keep with the opening to dome height ratio and make the door width plenty big enough for a peel and you'll be fine. Most people keep their pizza fire going on one of the sides (or back) and then use the opposite open hearth for cooking. Make some "cardboard pizza" cutouts and use your mock up to test what works for putting the fake pizzas in with your peel, turning them, and bringing them out. That should help you more than anything. Based on your pictures, I'd consider making the inside cooking hearth bigger (wider). It doesn't look to me that you will have enough space to cook anything more than one small pizza in your present mockup...just a couple brick widths will make a big difference.

[Lburou]

Re: Newbie looking for advice

Hello Denis

Your mock up of your floor and walls is a wise thing to do. With regard to leaving space for insulation, there is a fairly easy correction for you. Cantilever is the word of the day

Several of the ovens chronicled in the link Mike suggested show how to use your existing base and extend a new base beyond your current base, giving you more room in any direction you choose. At this point, it is easy to do. The ovens in the link are a different style than you are planning, but the cantilevered base carries over to your situation. Study the steel reinforcements and the wooden forms and you will see how to do it. The youtube video at the bottom of that post will give you a leg up in your planning.

If you choose to cantilever, your oven floor will be about four inches higher than you originally planned. It will be fine, mine is around four feet tall and I like not bending over to use it.

Good Luck!

[Denis Li]

Re: Newbie looking for advice

Hi Mike, Hi Lee

I've been playing with the bricks some more today and decided to go with Mike's advice of widening on the sides. I'll just add one brick width on each side (the space on the left will be used later for a small open barbecue foyer and the space on the right will have a small work space).

I guess i will have to use cantilever to extend the sides on the middle table. That would help gain some space for insulation. I'll wait for when i obtain the perlite to do the extension followed by the floor insulation.

thanks for the tips i'll post photos when i progress
cheers
Denis

[Denis Li]

Re: Newbie looking for advice

I've managed to locate some place that sells perlite. I haven't bought it yet but i got some sample. It feels very light and you can crush it quite easily between your fingers, is that normal?

I've also altered the design and made the floor wider (see photos) and made some preliminary dome drawing on a wood board.

About the dome, i used a pencil with a string to draw part of a circle on the board. but the bricks didn't fit too well so i adjusted the arc a bit lower. Is it important that the very centre of the dome has a single brick that serves as keystone? or is it still ok if i have 2 bricks around the centre of the dome? (i hope what i wrote is not too confusing)

[mrchipster]

Re: Newbie looking for advice

I've managed to locate some place that sells perlite. I haven't bought it yet but i got some sample. It feels very light and you can crush it quite easily between your fingers, is that normal?

Pearlite is quite brittle and does crush easily between the fingers, it is the fact that it is largely air and slows the movement of air that give it its insulating properties.

Chip

[brickie in oz]

Re: Newbie looking for advice

Is it important that the very centre of the dome has a single brick that serves as keystone? or is it still ok if i have 2 bricks around the centre of the dome? (i hope what i wrote is not too confusing)

This keytone thing is just a laymans myth.
Every brick is a keystone in an arch, try taking just one out and see what happens.

[Gulf]

Re: Newbie looking for advice

I wasn't thinking about keystones when I installed these. I was just conscerned about spacing.

[SableSprings]

Re: Newbie looking for advice

Denis, notice that Gulf put in some small wedges to help solidify the arch, reduce the gaps, and consequently save on mortar. You'll definitely be better off if you can either cut a slight angle on at least the corner bricks or use a starting wedge to reduce the gap on top of the dome curves. In addition, using some alternating split bricks to keep each dome row's mortar seams from lining up (with the adjacent rows) would be a good thing. The offset would just help keep a crack from forming & running along a mortar seam front to back...and seems like a good strategy to me.

On looking at your mock up, it appears from the pictures that your bricks are not actual fire bricks. I wondered if these are just standard bricks that you are using for a mock up or what you will be using in your build. Fire bricks in the U.S. are larger than regular bricks, so if these aren't the actual bricks you are going to use, it will make a significant difference in the oven dimensions. I think that although regular bricks will work fine for you in this application, they might spall a bit more over time than fire bricks and will most likely need a little more care/time when curing the oven.

[Denis Li]

Re: Newbie looking for advice

Hi all

Thanks for the recent posts and answers to my questions. i still haven't had time to get my perlite (i work the week in the forest) but hopefully next saturday i'll get off work earlier to buy it

Yeah, when i did some reading i noticed my bricks are not the same dimensions as the ones in the US. They are sold as refractory bricks though and are what i am planning to use for the oven. are they much different from fire bricks? the width of the brick is 5cm, quite thin, so splitting wedges could be tricky for a layman like me. i'll try to split wedges at least for the corner of the dome i think

[SableSprings]

Re: Newbie looking for advice

Yeah, when i did some reading i noticed my bricks are not the same dimensions as the ones in the US. They are sold as refractory bricks though and are what i am planning to use for the oven. are they much different from fire bricks? the width of the brick is 5cm, quite thin, so splitting wedges could be tricky for a layman like me. i'll try to split wedges at least for the corner of the dome i think

On your post (#7) the space between the 2nd and third brick of the arch is the one with the most "space" and is the one where I'd try to put in a wedge. The wedge simply reduces the amount of mortar you have to use and makes it a little easier to get the dome curve started. In other words, if you are uncomfortable with splitting wedges off with your brick saw or chisel, the mortar will work fine instead to fill in the gaps. As long as you've got a template arch to set bricks on for each row, they'll settle in and hold just fine.

As I understand it, refractory and fire bricks are basically the same thing. Although we are lucky in the US that our firebricks are fairly standard sizes, it doesn't mean that you can't build a fabulous oven with non-standard size bricks. Minor differences in widths and thicknesses should not be a major problem...might make you do a few slight adjustments, but won't halt the process. If your brick lengths vary significantly, you might want to select out enough bricks of the same approximate lengths for convenience to complete each row. (But nobody is going to come in and say all your bricks must be exactly the same size to have a proper working oven.)

[Gulf]

Re: Newbie looking for advice

The wedges that I cut are not full width brick. They were cut from the 2"(5cm) side. Much easier to cut that way. It allows the use of scraps from the dome build, too. It takes 2 wedges to fill each joint. One in front and one in the back of the arch.

[Denis Li]

Re: Newbie looking for advice

Hi All

I've poured my layer of perlite-cement mix on the concrete table yesterday and hopefully, place the floor bricks next week end. i'll post photos next week end.

Cheers
Denis