rehab of older oven

[dog-gone-estate]

I am new to this web site. I built an oven about 4 years ago and it has gotten a lot of use! At the time I built it I was not entirely clear on insulating materials and what would be best. I have decided to do a little "reabbing" of my oven which will include using 3 inches of thermal blanket (ordered through forno). I am then going to do a walled enclosure with steel studs.

My question is this. On my current oven - whcih is the traditional igloo shape - I have cement over the vermiculite cement - there are cracks in it - which shows what I didn't know then when I was building the oven - can I leave the cement on and cover this with the blanket? Or should I remove the cement?

[Dutchoven]

Re: rehab of older oven

My opinion is that if you can remove any of the existing materials to get to the actual oven bricks you will then be able to put the most efficient insulator closest to the dome...then you could do your walled enclosure and fill it with loose vermiculite
Best
Dutch

[Xabia Jim]

Re: rehab of older oven

It sounds like you have an insulation layer with a cover of stucco...is that right? How thick is this cement skin and how much of a heat sink will it be? Will you use the oven for roasting where you might be happy with a little extra heat storage?

I guess it depends how bad the cracking is too!

[dog-gone-estate]

Re: rehab of older oven

I have about 2-3inches of the vermiculite cement over the oven dome and about one inch (as best I can remember) of cement over that.

I had not planned on using any loose vermiculite since I will be using a 3inch (probably closer to 4 1/2 inch) covering of the ceramic blanket.

I do, on ocassion roast meats in the oven, but primarily it is a pizza oven.

[Neil2]

Re: rehab of older oven

"I have about 2-3inches of the vermiculite cement over the oven dome and about one inch (as best I can remember) of cement over that."

When in use, does the outside of the concrete get very hot, say over 180 degrees ? If not, then your oven is "reasonably" well insulated now.

If you want more insulation, I agree with Dutch. Tale off the outer 1 in concrete shell.

[Padilley]

Re: rehab of older oven

I am rebuilding an outdoor 42" inch modular oven I brought from Italy in 1994. Instructions for building was verbal and in Italian, which I was not fluent in. Not having a forum like this (or even an Internet) I did not insulate properly and the fiberglass used for dome insulation gradually compressed to nothing. It has cooked many pizzas over the years, but if the oven hasn't been used in a while, I had to fire it for three days to get 2 hours of heat for pizza. It never held heat long enough for baking.

I have removed the complete dome and hearth. The dome is five pieces of red brick cast in concrete each piece weighing between 200 and 300 lbs. The side pieces were cracked and split. The big top of the dome piece is cracked, but still in one piece.

The hearth is red brick and many are cracked and broken. The vent and outer arch is a one piece refractory item that is built into a stone wall and will stay. I have evacuated below the hearth and I have 2" of 8 lb ceramic board to go under the brick and 2" of ceramic blanket to wrap the dome. I will isolate the dome from the outer arch/vent with ceramic insulation. When finished, the dome and hearth will be completely isolated from any other material by 2" of ceramic insulation.

Questions:
1. Is this red brick that came from Italy, real firebrick or just ordinary brick?
2. If buy new firebrick for the hearth, how can I tell if it is the right type? (I know the difference between insulating and that used to line a fireplace.)
3. What should I use to join the broken pieces of the dome? I have Forno Bravo's refractory mortar, should I use that or that black fireplace repair stuff from Lowes that was mentioned elsewhere in the forum?
4. The top of the dome is cracked, but in one piece, how do I repair it?
5. The dome is built to rest directly on the bricks from the hearth, should I mortar the base of the dome to the hearth bricks?
6. Did anything above indicate I am doing something wrong?

[Dutchoven]

Re: rehab of older oven

Questions:
1. Is this red brick that came from Italy, real firebrick or just ordinary brick?
2. If buy new firebrick for the hearth, how can I tell if it is the right type? (I know the difference between insulating and that used to line a fireplace.)
3. What should I use to join the broken pieces of the dome? I have Forno Bravo's refractory mortar, should I use that or that black fireplace repair stuff from Lowes that was mentioned elsewhere in the forum?
4. The top of the dome is cracked, but in one piece, how do I repair it?
5. The dome is built to rest directly on the bricks from the hearth, should I mortar the base of the dome to the hearth bricks?
6. Did anything above indicate I am doing something wrong?

1. Most likely it is some kind of refractory material.
2. Firebrick for constructing a fireplace is all you need...just make sure they are about 2.5 inches thick as opposed to the splits that mason's sometimes use for relining fireboxes
3. If you have the refmix use it...it will be the best material to repair the cracked pieces
4 If it is still in one piece you may just want to leave it as such...IMHO...once it is back as part of the oven it will once again be under compression...
5. It is not necessary to and some would say it would impede the dome's expansion and contraction relative to the floor
6. Quite on the contrary I think you are doing a great thing...glad to have helped in some way...since yours is a modular oven be sure and check out the threads in this section...
Best of luck!!!
Dutch

[dmun]

Re: rehab of older oven

James has said that some of the ovens competing with the FB products are made of ordinary fired clay "terra cotta" rather than refractory material. This would explain the red color, and the cracking you are getting. You could put the existing dome on a new insulated firebrick floor with good results. Just having proper modern refractory insulation will make a world of improvement.

And yes, the ordinary firebricks from a masonry supply are the ones you want. There's no need for High Duty bricks in a home oven.

[Padilley]

Re: rehab of older oven

Dutch & DMUN,

Thank you for your input. Forno Bravo and its forums is great! I have printed and read all of the instructions, (Installation, construction, picking bricks, etc., etc) from the site and made a book for current and future reference. I have followed many of the forums. Total, I must be approaching 100 hours of research on this project. Once I figure out how to link pictures, I will be more of a contributor.

I have purchased firebrick, two plus inches thick, and I am removing all the old brick from the hearth (again!). This unit sets into the ground with the top of the dome just about ground level. It is sitting on a cement block base and has a cement block enclosure around the dome. I have chiseled away a hundred pound or so of concrete from the inside to provide plenty of clearance for the insulation. Thank God for pneumatic hammers! I have now spent about forty hours in a 4' square hole about 4' deep.

BTW This oven was purchased in Italy and has a BF cast above the entry. Any idea who made it?

I am concerned about moisture entering the through the outer shell of the enclosure. It is not water proof, however, it is well drained with considerable effort made to move rain water away from the fireplace. If it is a problem, I will evacuate around the enclosure and coat it with some sort of water proofing.

This project is consuming more time than anticipated. For the last 14 years, on the third weekend of April, we celebrated my son's birthday with the first pizza party of the season. Between children, grandchildren, cousins and inlaws, we serve 25 to 35 people and about that many pizzas. This year it looks like it will be the first weekend in May.

[Padilley]

Re: rehab of older oven

A rain hit my partially assembled hearth soaking the ceramic board. This stuff has no strength when damp and soaks up water like a sponge. I can compress this wet stuff between thumb and forefinger, if it gets damp, it will never hold a ton of masonry. I live in North Carolina, it rains a lot here. I cannot guarantee that it will always be dry.

Unless someone has a better idea, I plan to pour a 2" layer of vermiculite cement on the floor of the enclosure, then pour a 2" ledge around the perimeter to support the hearth firebricks under the the edges of the dome. Inside the dome, the firebricks will sit on the 2" of ceramic board insulation.

I have read most of the installation threads and have never heard a concern about the wet strength of the ceramic board.

Has no-one else run into this problem?

[Les]

Re: rehab of older oven

I left some of my scrap board outside for the winter with many pounds of weight on it. It seemed to survive fairly well. I know what you mean though - when I was leveling my hearth bricks with wet fire clay, it was tearing it up pretty easy. With that said - I try very hard to keep any rain off the product. I have a huge vent cap and I place a piece of tile over the vent when I'm not using it.

Les...

[dmun]

Re: rehab of older oven

Which refractory board are you using? The only problem like this we've heard reported is Ken's problem with Kaowool:

http://www.fornobravo.com/forum/f6/k...oard-2588.html

Both the Cal-sil board and the stuff I used (H-W insbloc19) will stand up to occasional wetness.

[Padilley]

Re: rehab of older oven

This is the board I used

From Mcgills:
2" CERAMIC BOARD. Density: 17.5LB/FT3 or 280KG/M3 Size = 2 ft x 3 ft x 2 in. Working temperature = 1000 Celcius or 1832 Fahrenheit. Maximium temperature = 1260 Celcius or 2300 Fahrenheit