The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Are concrete bricks safe for a brick oven?

varda's picture
varda

Are concrete bricks safe for a brick oven?

Hi.   I am in process of building a small and simple brick oven.   I bought Kiko Denzer's book, and am using some of its principles, and also the lovely picture that someone on this list referred to which shows an oven of stacked bricks.    So far, I've dug a hole as far down as I could before I hit ledge.   Not very far.   I filled the hole with small rocks that I found around, and then poured in 200 pounds of gravel on top of that.   Then I put down a layer of cinder blocks, and then foot square granite slabs on top of that for the oven floor, which incidentally Denzer recommends against, but they make a very nice surface.  Now it's time for the brick walls.   I was shopping at home depot and found some very nice and inexpensive red bricks.  They are labeled as concrete brick.   Now that I'm making the part of the oven that will contain both the fire and the food, I started to wonder whether these materials, that were really made for landscaping,  will be safe for food.   I have no reason to think they won't be, but then on the other hand who knows how things are made these days.   Does anyone have any information about this?   I could try to reach Old Colony, the manufacturer, but what with liability law, I doubt I would get any real information.   Incidentally, it never occured to me that the gravel could be a problem, but after dumping the third 50 lb bag of it, I read a warning that says it may contain silicon dust, which I think is only a problem until it settles, but I should have worn a mask while I was dumping it.   I thought gravel was just gravel.  Thanks for your help!  -Varda

Roo's picture
Roo

I have just started my oven and will be using fire brick.  It is a Alan Scott Oven and he calls for either fire brick or common red brick.  Not sure if that is what you are talking about, but perhaps your Home Depot could provide you with information.

Faith in Virginia's picture
Faith in Virginia

Be careful of bricks and that granite exploding. When you get something like that really hot they could fail or explode I think the granite will break apart or do something like spalling.http://www.interfire.org/features/spalling.asp

La masa's picture
La masa

Lots of ovens are made of granite here in Spain.

idiotbaker's picture
idiotbaker

hi.  I've been looking into the smaller Alan Scott ovens too.  I don't quite have the bread thing down yet, but I'm sure it's because I don't have the right oven!;)  


How's it going with that?  What part of the country are you in? I'm in NC.  Very interested to follow your experience as you build.  Keep us informed.

varda's picture
varda

The home depot stuff is concrete, which I am hearing will not work.   Common red brick is clay, and so apparently is fire brick but a different type and composition.   So I am dropping the concrete brick idea and will go back to clay brick.  Good luck on your oven.  -Varda

Crider's picture
Crider

will quickly deteriorate in the heat. They're not much different than cinder blocks except for the color and size.

varda's picture
varda

Do you think that clay bricks will survive the heat better than concrete bricks?   I was planning to use fire bricks (which I thought were also made out of concrete) for the ceiling only - which I figure is the hottest part of the oven.    I decided to go with granite for the floor because I had been using the same thing for a bread stone for several months, and it seems to be able to take the heat.   The material is called Arctic White which is an inch thick unpolished Finnish granite.   My indoor oven temperature gets up to 550 deg I think, and I figured the floor wouldn't get as hot as the ceiling in a small wood fire, but I guess I'll find out soon enough if the granite will survive. -Varda

pdiff's picture
pdiff

The oven floor can easily hiy 1000 F or more under the fire.  The granite may crack due to thermal expansion.  I assumeit is bigger than the stone you are using.

varda's picture
varda

These are 1 ft square, 1+ inch thick stones meant to be used for walkways, I think.  Exactly the same as what I am using in my regular oven, without difficulties.   I was planning to use 9 of them for the oven floor.  Another poster said that granite ovens are common in Spain.   Perhaps granite type?   Or size of fire?   I can't believe a fire I would make in a small oven could get even close to 1000 F but what do I know.   I have zero experience with this.  Thanks.  -Varda

pdiff's picture
pdiff

I'm not sure what is "small" for you.  I cook in a 42" diameter all fire brick dome.  An infrared themometer aimed at the floor at the bottom of the fire goes off scale and the IR tops out at 1000 F.  Pizzas typically cook at 700-800F.  The idea for bread is to soak the oven in high heat (at least the 700-800 F), let things stabilize, and then get the temperature down to 400-500 for baking.  So while you might not use the oven at high temps, it often passes through those temps before use.  The other thing to consider here is the mopping of the floor before baking.  This cleans the floor, but involves a wet rag or mop.  Make sure the granite can take the thermal shock (fire brick or good clay brick can).


Having smaller pieces would help as they could expand and contract independently.  If they are cheap enough, you could experiment and lay a few on the ground and build a large fire on them.  After the fire burns at least an hour, brush off the ashes, and sweep a damp rag across them. 


Their stability would also probably be dependent on exactly what type of granite it is.  The stuff we used to have in Colorado was quite fractured and broke easily, but it wasn't something you would make garden stones from.  Yours is probably better quality.

varda's picture
varda

I bought these at home depot, and of course the staff had no idea what they were.   They were labeled Arctic White, which I googled, and it is the name of a granite from finland.   It looks pretty rugged, but who knows.  Since I've already bought it, and it was pretty cheap, I might as well just use it, and if it works (or falls apart) I can report back to the list.

La masa's picture
La masa

I've found this two pics:




I think both of these ovens have a brick dome, but both of them have the floor near the door and the jambs and lintel made of granite. They seem to have survived a good number of years.

varda's picture
varda

These are massive slabs.   My pieces are tiny comparatively.   It is nice to see how people do these things in different places and times.  -Varda

yozzause's picture
yozzause

Hi Vahimo,


If you go to traditionaloven.com RADO has a whole list of materials that can and can't be substituted. Some are a real risk, with clay house bricks apparently the creams are better than reds at withstanding high temps and that is to do with the clay being used. You have to do a comparison and based on what  you  think you will save which invariably is not a huge amount and what it will cost to do  AS RECOMMENDED. If you are going to get advice from someone that has the knowledge, and we are not talking just a simple post here, you should at least follow their recommendations. It is like asking me how to make a certain style of bread and then changing the formula and substituting the main ingrediants and directions only to be surprised that  you have made something you can't even eat let alone pass off as bread.


The only time that i would contemplate substituting would be if the recommended product was unavaiable and then i would go for the next closest thing not a completely different material.Again on Rado's web site he has people from all over the world that are  needing to substitue materials out of necessity.


You will invest a lot of time and effort into this project  make sure it will be something that you can admire and know that is as good as it can be rather than i wish i had of this or that.


In England they have some very interesting structures built all over the place usually in prominant positions and of no particular use called FOLLEYS make sure you dont build one of those for yourself.


i am reminded of the guy who lived on a council estate where all the houses are the same he says to his neibour i'm about to re - paper the walls, youve just done yours how much did you buy? and gets told 24 rolls. About a month later the two meet and the guy says you told me you used 24 rolls of paper, i have 5 rolls left over, to which the reply was so did I. 


Regards Yozza   

SylviaH's picture
SylviaH

My daughters beautiful oven is all done with fire bricks ceilings, walls and floors..there is a large very thick maybe over 3" shelf of solid granite that sits on the outside front of the oven..its the landing shelf just outside of the oven door.  Once the oven was fired very hot and the granite shelf got a hair crack at the front.  I think I would use fire bricks because that what they are made for and can withstand the heat....IMHO.  I have a forno bravo pizza oven with a cement flooring that also works and holds up to very high temperatures.  I've had it heated up to over 900F with no problems.  They use a 'special mixture' in their cement to take the heat.  I hope this helps a little in your decision.  Stay safe and know your products limits and uses.


                       daughters oven- granite shelf- these ovens can get over 1200F  


                         


                                                                                  ^hairline crack here


Sylvia


                       


                   

varda's picture
varda

Gorgeous oven.   Thanks for your comments!

ivrib's picture
ivrib

Hi Varda,


I have a good bit of experience with clay/mud ovens built according to Kiko Denzer's system.


These are my comments:


1) concrete bricks or any regular concrete product is made with portland cement - this is usually a grey powder (sometimes white) which gives cinder block its grey color. This material cannot stand up to high temperatures. It disintigrates at the temperatures of oven use. On the other hand any clay product is much more refractory, meaning it will withstand high temperatures. The only concrete products fit for and oven are made with a special cement called aluminate cement which is sold specifically for the purpose of high temperature use.


2) firebrick is a type of clay brick, not concrete, made using fireclay which is a type of clay that is fired at very high temperatures. Common red CLAY bricks and not concrete are also suitable for an oven, especially a small home oven which will not be used continuously like a commercial oven. For an oven made for heavy use all firebrick should be used.


3) From your description of the bottom layers of the oven it seems you didn't include an insulation layer in the oven. This layer is extremely important. When you use your oven your fire heats up mass which then heats food which is placed in the oven cooking space/on the hearth. If your oven is not insulated, instead of all the stored heat going into the food to cook it, a large part will be transferred into the surroundings, including downwards, and be wasted and your oven won't be able to cook for very long.


I have all kinds of tips based on my experience. Contact me at ibunis@gmail.com and I could maybe give you some advice based on what you're planning to use the oven for.

qahtan's picture
qahtan

Oh my, oh my, what a fabulous looking oven, I am green with envy, how I would love an oven like that,,, it is beautiful...  Many years ago I wanted a brick oven, (still do) I had all the plans and found the scource for the materials etc, and my husband just wasn't keen on the idea, boo hoo.......


Although I think I am too old now, I can look with envy at the one above and wish it were mine. enjoy... qahtan

del's picture
del

Never mention the oven itself, just what will come out of it i.e. fabulous hot pizzas, breads to die for, etc.


 


You see, this is how I can get expensive tools (power table saws, thickness planers, etc.) past the wifey. "What great cabinets and storage units I'll be making just for you hon...."


 


haha. (my secret is out.)


 


 


//del//

Futterbudget's picture
Futterbudget

so I asked him about your concrete bricks, and he said that they will crack, and the mortar used for ordinary concrete bricks will crack too.  They're just not designed for the heat.  However, people do it, and it works okay for a short time.  Just expect your oven to crack.  I asked him if the oven would fall apart, and he said it just depends on how it was built.  But eventually, yes, it would.

Macgyver54's picture
Macgyver54

No you can not use concrete brick to make your oven . Concrete brick are made for Lanndscaping , walls and walkways they are not made for high heat usage they will crack and crumble if exposed to the high heat of a brick oven. You needmto use fire brick these are brick that have been fired with a special glazing specifically for high heat uses . You can use your concrete brick for the outside of your oven but the inside ofyour brick oven has to be done with fire brick also there is a special powder that has to be mixed with the mortar when laying these brick in order for the mortar to withstand the heat as well . My Dad is a brick and stone mason and that is how he has told me and I have seen him do brick ovens and fireplaces. I hope that this will help you .

varda's picture
varda

Well the combined wisdom of the list says no to concrete bricks.   Thanks for all the advice.   I got a recommendation to use autoclaved, aerated concrete as an insulator under the hearth, and to give up my plan to use stacked bricks, and make a clay dome instead.   So onward and upward.   I just hope that I will actually finish this thing before summer baking season, since that was the whole point of the exercise in the first place.   Thanks again! -Varda 

pdiff's picture
pdiff

It's doable.  I got mine to a point where I could start using it within 2 months and a lot of that time was building the concrete base.  Have fun!