DIY pizza oven

May 7, 2006 9:39 PM

Do you really need fire bricks for a pizza oven or would house bricks do?
posted by wilful to home & garden (21 comments total)

My understanding is that regular bricks will explode if heated sufficiently, because they've got air trapped inside.
posted by Hildago at 9:48 PM on May 7, 2006

I suppose you're building an outdoor, wood fired pizza oven, and in that case, I think you need to use fire brick becuase of its ability to withstand extremely high temperatures.

I was typing out a response assuming that you're putting brick in your kitchen oven to bake bread/pizza on, but I guess that's not the case.
posted by scalespace at 9:59 PM on May 7, 2006

Yeah, anytime you heat rocks, you should be careful. Granite or limestone should be good. Don't use sedimentary rocks or anything that absorbs water (definitely make sure whatever rocks you use are dry before throwing them in), is cracked, or you think might have air pockets in it.
posted by dsword at 10:02 PM on May 7, 2006

Outdoor oven, yes, with a concrete and/or earth and/or brick rubble base, hemisherical top, outside lined with house bricks, inside lined with ???.

Wood fired.

Firebricks are hard to come by and expensive, as far as my research has discovered. While house bricks are cheap and plentiful. But what are the implications ?
posted by wilful at 10:03 PM on May 7, 2006

House bricks will crack. They don't explode because of trapped air. It's because they don't conduct heat as well as fire bricks so the stresses from greater temperature differentials will fracture them.
posted by weapons-grade pandemonium at 10:05 PM on May 7, 2006

Oh, followup I just thought of, a concrete base wouldn't be a problem would it? None of the designs seem to indicate it would be.
posted by wilful at 10:11 PM on May 7, 2006

House bricks will crack and become very brittle. After a while, you will notice big chunks flaking off. Eventually, it will eat holes right through the bricks.
posted by unixrat at 10:19 PM on May 7, 2006

Same principle applies to the concrete base. It's likely a good idea to add lots of steel reinforcing mesh to improve thermal conductivity and add resistance to stress. The side exposed to the fire is expanding quickly from the heat; the side underneath the oven is not.
posted by weapons-grade pandemonium at 10:25 PM on May 7, 2006

Nix lots of reinforcing mesh. It increases the cost and doesn't add an appreciable amount of thermal mass.
posted by electroboy at 10:36 PM on May 7, 2006

Heat can also degrade the chemical structure of concrete by driving off the bound water in the crystal structure.

Probably a good idea to have either fire bricks or a sacrificial lining of cheap concrete bricks that can be replaced if the base is going to bear the direct heat of a fire.
posted by Good Brain at 10:43 PM on May 7, 2006

Wilful,

If you have a pile of bricks from an old construction site, the quality varies from brick to brick. In old 'triple brick' construction the bricks that are used on the outside are stronger and more durable than the softer bricks used for the interior thicknesses.

The outside ones are called 'clinkers' because they make a muck louder 'clink' sound when struck with a hammer, The softer ones are called 'salmon' for reasons that I do not know.

The difference in quality is not due to the content of the bricks but the way in whick they were fired. They were fired in batches and the bricks that were located on the outside of the batch received more firing and are thus harder.

Back to your question, I am no expert on outdoor fireplaces or ovens but I think that you would definately want 'clinkers ' for your construction. This would mean that out of your pile of free and plentiful housebricks that only a smallish percentage of them would be worthy of your project. That is if there are any clinkers left!
posted by vidarling at 11:01 PM on May 7, 2006

Some great ideas here. More here.
posted by weapons-grade pandemonium at 11:28 PM on May 7, 2006

thanks for answers so far. What if the inside of the oven was rendered, would that defer any brick cracking issues?
posted by wilful at 11:35 PM on May 7, 2006

Not exactly the same situation, but both my parents are potters and I spent a lot of time building and tweaking kilns with my dad, as a kid. You definitely need to line the firebox with firebricks. Regular bricks will shatter and you will have very gritty pizza. Even though the pizza oven will be cooler than a kiln, it will heat up and cool down quicker. Also, if in the backyard, presumably it will be exposed to the elements and the bricks will absorb water, which will make them explode when heated.

Concrete will also shatter with exposure to heat. Probably ok in the oven part - which presumably doesnt get much above 500F. Definitely not in the firebox. Look into lining with hhigh-temperature mortar....

Used firebricks can be found in old kilns being thrown out by potters. Maybe phone around for decrepit kilns, or put a "wanted" ad in.. Also look into old, unrecyclable wood stoves, often lined with firebrick One time we got a bunch from an old locomotive, but that was a fluke. Remember, the firebrick is just a lining usually, not structural, and so you can often get by with fairly cruddy bricks -- they are soft and you can even saw them up with a hacksaw to fit.

Two other options might be, incorporate a cast iron firebox, maybe from a salvaged woodstove or something, into your oven. This will cover off a lot of your firebrick need. Also, look into chimney and flu liners from building supply stores -- they are built to withstand heat. Broken ones can be pasted together for a crude firebox insulation

Assuming you get some firebrick, you will need special mortar -- available in ready-mix tubs at big hardware stores. Regular mortar will explode.

Remember, you only need the firebrick where temperature are very high / direct contact with flames. Err on the side of caution! And also, wherever you have firebrick you still need to have regular brick on the outside -- fire brick is quite crumbly and doesn't suffer the elements well.

Finally, keep away from fibrefax and similar insulating cloths, or at least check up carefully on them -- many of these are carcinogenic. And, if you are messing around in old wood stoves or kilns or whatever, be very careful to avoid asbestos exposure.
posted by Rumple at 11:38 PM on May 7, 2006

A brick oven will reach 700-800 degrees under a full load of wood, firebrick would be preferable to concrete unless it's refractory concrete.
posted by madajb at 3:02 AM on May 8, 2006

Rumple's answer is good, but assume a design in which the firebox is different from the surface on which you cook your pizza. Most easy designs I've seen have one surface on which you first fire and then cook your pizza. It's the residual heat from the fire, and perhaps the coals pushed to the back of the box that do the cooking, not (like in a kiln) a continuous fire. Don't forget that pizza cooks in ~20 min, sourdough bread in ~50. Pottery takes 1-7 days in a wood kiln to fire properly. Don't let your desire to save money on the building lead you to make a crappy oven.

The Bread Builders: Hearth Loaves and Masonry Ovens discussed what goes into a good oven, which is pretty much the same for bread or pizza.
posted by OmieWise at 5:52 AM on May 8, 2006

This page has a good discussion about ovens and firebrick.
Basically though, the really expensive firebricks are the lightweight insulating ones (suitable for a kiln) and are not what you need. The cheap "fire brick" that is used to line fire place boxes should be fine.
Anything that is too wet might explode in an oven, so heat slowly the first time. You may want to contact some of your local solid surface counter top people and see if you can get some scrap from them. A nice piece of soapstone would make a great surface to cook on.
posted by 445supermag at 6:35 AM on May 8, 2006

When I built my outdoor clay wood-fired pizza oven, I stopped by a masonry store in town. The usual home improvement stores did not have fire bricks (and the staff didn't even know what I was talking about, going so far as to say regular bricks would work just fine).

The masonry store was not an "open to the public" kind of place -- their customers were builders. But the fellow there was very helpful, and when I explained that I only needed about a dozen bricks, he essentially gave them to me -- he had no mechanism for making such a small sale.
posted by ewagoner at 7:15 AM on May 8, 2006

Not to hijack a thread (but here I go)...any idea where one might buy, say...a 14 inch by 14 inch firebrick/stone to line a home oven with?
posted by griffey at 7:48 AM on May 8, 2006

Rumple: it's Fiberfrax, as in refractory.
But yes, if you're buying used firebricks, be wary of contamination with asbestos.
posted by weapons-grade pandemonium at 8:00 AM on May 8, 2006

To griffey: Williams-Sonoma gots em'.
posted by sgobbare at 8:51 AM on May 8, 2006