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karl 07-01-2008 01:17 PM

Tiles expansion

I am new at the forum. I submitted a question to Forno Bravo on their web site and received a reply (I think it was automatic) that I should use the forum where a lot of experienced people discussed related issues. My question was:

I am starting the buiding of a 36" pizzaoven and using the Forno Bravo drawingsand descriptions (Pompeii Oven Plans). The fire bricks i am using have an expansion of 0.65% (at 1000 C). The instructions recommend to set the floor tiles in a paste of sand and fireclay. I am worried that this may restrict the expansion of the tiles (calculated expansion is about 8 mm over the floor lenght). Can you comment on this issue? I am using the oven mouth as the fixed point. Am i assuming right when i conclude that the first round of wall bricks, which sits on the floor itself, should not stick to the floor itself? kind regards from karl
Do you have any input or advice on this issue.

Regards from karl

Jim Bob 07-01-2008 02:01 PM

Re: Tiles expansion
I too am a real novice at this oven building, but I do know that if you convert 1000 degrees Centigrade you are talking about 1832 degrees Fahrenheit. Way above I am told where i will be cooking (400- 800 degrees F). Not sure how much expansion you will actually experience at that level. I am interested to know about whether or not mortar is used on the bottom of the first course or not. My contractor will be doing it tomorrow.
Good luck with your oven.
Jim Bob

karl 07-01-2008 02:20 PM

Re: Tiles expansion
You are right. I used the expansion number on the data sheet and as you say it is stated at a much higher temperature. I guess a more realistic temperature would be 2/3 of this. Maybe the expansion is linear with temperature in that range? If so about 5 mm max linear expansion across the 36" floor should be expected?
I would love to hear what your contractos say about using mortar on the first course.

regards from karl

Jim Bob 07-01-2008 03:25 PM

Re: Tiles expansion
Those FB specs are handy but of course impossible I guess to cover all contingencies. But somewhere, perhaps in this forum I have read about the mortar situation. I just cannot find it now that I really need to know. Unfortunately I cannot leave it entirely up to my hispanic brick mason. He has only built one or two of these type ovens. He does a lot of fireplaces, and is a very good mason, but they don't deal with the same sustained high temps we are talking about here. Even when I know the right answer I still have some difficulties communicating that info to him. His English is minimal and my Spanish is non existent! I know, I need an interpreter!

Jim Bob

Ed_ 07-02-2008 06:13 AM

Re: Tiles expansion
I can't seem to find any data sheets for firebrick that include thermal expansion coefficients, but for alumina it's 5.4x10-6 per Kelvin. If we assume (dangerous, I know!) that firebrick is about the same, then an increase of 500C would cause an expansion of roughly 0.3%.

That's only a couple hundredths of an inch per brick, so I wouldn't worry about it. Besides, there have been a lot of successful builds from these plans!

naples 07-02-2008 07:05 AM

Re: Tiles expansion
I'm new to the group and have not started building my own WFO yet, but have heard that mortar is not used on the bottom of the first course. The bricks should only rest on the oven surface.

But as I mentioned above I'm new to this and am not a brick mason...just trying to gather as much info prior to starting.

If I'm incorrect hopefully someone else will correct me. :o

JAG 07-02-2008 09:54 AM

Re: Tiles expansion
Karl, Jim Bob,

I to am a novice to building ovens. I finished my first and only oven about six months ago, and so far it is still standing and even better still cooking. I was a visitor to this sight long before I decided to do my build and read over many of the threads here and the Pompeii plans until I could probably recite them backwards. Anyway what I took away from all of this is that the bottom layer of fireclay, sand and water will make a nice paste for the floor bricks to set on and since there is no cement the mix will not set hard but remain as a sand type layer. Like laying patio bricks, it helps you set the bricks so they are nice and flat with each other and no edges sticking up to catch your peel on.

Jim Bob,

From most of my readings do not cement the first (soldier) course to the floor bricks. This will allow horizontal expansion across the floor without stressing the wall to floor interface.

I am just a novice at this so it may be wise to research more yourselves or wait for a professionals reply. There are many here at this sight that will give you better insight to your questions but I believe the answers will basically be the same as mine only more informative. Hope this helps.


Jim Bob 07-02-2008 10:14 AM

Re: Tiles expansion
Not sure how you had the patience to read thru this forum day after day and not get right into building one of these ovens!! But obviously that is the smart way to go and you don't end up asking a lot probably silly questions. It is risky to learn as you go, if you don't learn fast enough. That is my case. But I think things will turn out fine and we are starting on the oven floor as we speak. Had to drill holes first for the thermocouple leads to the thermometer first. I will be fighting the styrofoam forms next, trying to cut them perfectly to size of the inside of the oven. It doesn't look like Rocket Science, but I still can screw it up!!
Jim Bob

Breven 07-02-2008 10:20 AM

Re: Tiles expansion
I agree with John. I'm following the FornoBravo plans and getting ready to start my floor and dome this weekend. I'm making a paste out of fire clay (also called mortar clay) fine sand and water. Spreading it with a notched trowel so the floor bricks (in a herringbone pattern) can be seated level. Just follow the FB plans...these guys are experts. Build it to their specs and your oven will live a lot longer than you will!


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