Newbie question about oven floor

[Puckncrazy1]

I'm having an oven built for me and told the contractor that we need at least a 4" base of insulated concrete to set the firebricks on for the oven floor. That was not done, instead I have 2 layers of firebrick on a massive base of concrete filled, concrete block.
Will this design work? Will this oven ever get hot enough to use and will it maintain heat?

Thanks
Jay

[Laurentius]

Re: Newbie question about oven floor

You're paying him? Have him to build it right! Once its finish it too late too costly. Provide him with details of your insulated concrete mixture, the info is on the forum. You should check each phase of the build, these guy are experts but not in the field of WFO. You don't want to end up with a White Elephant.

[Tscarborough]

Re: Newbie question about oven floor

Remove the firebrick and put the insulation in.

[Faith In Virginia]

Re: Newbie question about oven floor

They make an insulation fire brick. Insulation brick can work fine. If it is the regular fire brick that is for the floor and dome. Stop him now and get some insulation under there.

[Puckncrazy1]

Re: Newbie question about oven floor

so... this is an unconventional oven... the oven will be sitting on a 4' solid cube of concrete plus the 6-8" slab it is sitting on. I had free concrete blocks so the whole base is concrete filled concrete blocks.
My guy thinks that the two layers of firebrick sitting on that massive chunk of concrete will maintain heat and thinks that insulation under the firebrick is for ovens that don't have this solid base like we have.
Thoughts?

[deejayoh]

Re: Newbie question about oven floor

The base will suck the heat out of the oven - and the bigger the base you have, the worse the problem will be. You want to direct all the heat from the fire into heating your firebrick. Without insulation, the heat gets dissipated into the slab, and you'll never be able to maintain a hot enough floor for cooking.

As others have said, get some insulation in there before you go any further.

[Puckncrazy1]

Re: Newbie question about oven floor

Will the 2" thick Alumina Silicate board be enough insulation between the firebrick and the solid base?

[shuboyje]

Re: Newbie question about oven floor

Fire the mason and get one who can listen to simple direct instructions from his customer. I work in large commercial construction for a living, if I ignored the direct request of the customer I would no longer have a job. That's the easiest part of construction, the guy with the money calls the shots. If you are an expert in your field you may sway their thoughts, but they still make the final call.

[RTflorida]

Re: Newbie question about oven floor

Pull up both layers of the firebrick , add the 2" board and then top it with one layer of firebrick. The 2" board is the equivelent of 4-5" of insulated concrete, you should then be fine.

Fire the idiot, if you leave it the way it is you will have the largest heat sink known to man. It would NEVER, EVER get up to temp and certainly not maintain a temp. He may me a fine mason, but he certainly is not an oven builder.

RT

[Neil2]

Re: Newbie question about oven floor

"My guy thinks that ...."

I second Shuboyje and RT. Get a new "guy".

If he is going to screw up and argue on this, He is likely to screw up and argue down the line.

[Faith In Virginia]

Re: Newbie question about oven floor

I will offer my phone number to your mason if he needs to talk about his error in thinking. Let me know and I will send it in a private message. I have been talking with an experienced refractory mason with many years of experience. When we talked about the necessary insulation under the oven he was unaware of the heat loss in a downward direction. As the others said stop the progress now. Fire the guy only if he refuses to fix the error.

[Puckncrazy1]

Re: Newbie question about oven floor

Thanks everyone... I really appreciate your responses!! I'll let you know how things go..

[Bacterium]

Re: Newbie question about oven floor

Jay,
Too add to what has been said so far........I can speak from experience on this.
Search for an oven build post for "Redgum Roarer" and you will see on my first oven build that I didnt insulate underneath the oven floor. Basically it was concrete slab then a small layer of sand then the oven floor bricks. Yes the oven worked to a degree but it clearly got hot underneath as it lost heat through the floor.

About a year or so later I helped a mate with his oven which he built with an insulating layer under the floor. Having cooked in both ovens the comparison was....
His tended to retain better pizza temps on a long pizza session from less wood. Next day his oven was around 300deg celcius whereas mine was 100deg at best.

Basically my oven could do pizza and bread baking all on the same evening, so it was dropping down to the 250deg celcius before the night was out. His oven had a decent amount of retained heat the next day which meant he could do a roast or 3 decent loads of bread.......whereas I had to refire mine the next day. His wasn't hitting the 100deg c mark until well into the third day.

Sure my first oven did work, used more wood, was more challenging to keep the heat up for slow roasting and bread baking. Now that I have a chance to build a second oven ( see Bacteriums 2nd build) I'm definitely insulating much better and trying to shoot for 3 days of retained heat..............the constant echo on here insulate...insulate....insulate is true and tested.

All the best with you planning and hope the detail helps you work through it.

[WJW]

Re: Newbie question about oven floor

Fix it.

The guy that gave me the idea to have a wood fired oven has no insulation in his floor. He bought a kit from FB and had a contractor "experienced in building pizza ovens" build his oven.

The guy laid out a masonry stand with no insulation...lots of concrete block and rebar with a modular FB kit sitting on top of it. I don't know which one but it appears to be about 30 inches in diameter. He can cook pizza in it. That's pretty much it. And even with pizza he needs to move the pizzas around constantly or the floor gets too cool to cook well.

The massive masonry stand acts like a giant heat sink which sucks the heat from the floor into the stand and then into good old planet earth. His wife is a trained chef and a fantastically good baker. Yet she has never successfully baked a single loaf of bread in the oven in the twelve years since they built it. The only way they could bake bread would be to burn a fire for hours and hours and hours to the point that all that mass below the hearth was so saturated with heat that the heat loss below made no difference because the area saturated was so large.

I did my first big pizza and bread bake a week ago and they came over. He was blown away over what a difference the floor insulation made.

My advice is as said previously...pull out the bottome layer of firebricks and replace it with a correspondingly thick layer of ceramic fiberboard insulation to isolate that hearth. Then go with a single layer of firebrick for your hearth.

Bill

[Gary Mots]

Re: Newbie question about oven floor

This site may help concerning heat loss and info on your insulation problem with your contractor. GlobalSpec - Engineering Search & Industrial Supplier Catalogs , there's a lot of varied info on many subjects.