Heat Break Materials

[paulkjrobbins]

Hello All,
I am doing a 36" pompei in Provo, UT. I am trying to finish before it gets too cold. I just have a six-inch hole in the top of my dome to fill and I can go on to the gallery! I am getting into the particulars of how I am going to build my gallery I am not quite sure how to go forward on a couple of points. If there is anyone out there with advice on the following I would be so appreciative! I am trying to build the oven to last and to retain heat as long as possible and to be done before it freezes here!

For the outer arch, I am thinking of using a 3" thermal insulating brick for the first row of bricks that butts up against the inner arch. It would have a 1 1/2" square notch cut out of it to saddle the inner arch (some have referred to this as the L-cut brick). I would then build the remainder of the gallery coming out with firebrick (cheaper)

A, If I am using insulating firebrick, will graphite fiberglass rope improve performance at all?
B. If I use graphite fiberglass rope. I will cover the floor gap with a piece of SS. In the ceiling however it will be exposed at the gap. Does rigidizer do the trick of keeping it from getting into the air/food?
C. I have heard that insulating fire brick is VERY fragile. I also know that others make galleries out of them. Has anyone seen issues with them breaking because the pizza paddle hit them or something similar?
D. Since I will be mortaring them to the rest of the gallery via homebrew, does anyone know if there are any issues with it adhering to homebrew? Do you pre-soak them like with normal firebrick?
E. See picture below - I have been wondering what this is since we bought this house a year ago. The last owners left this roll and a bigger one. To give some perspective, it is only 1 1/2" high off the table and 2' long. This roll weighs 60 pounds. It is some kind of flexible metal sheeting about 1/8" thick. I am guessing it is not aluminum since it is so heavy. That leaves SS Foil or lead. I am hoping someone knows a way of telling. If it is some kind of SS foil then I will incorporate it into the heat break. Probably not the brightest idea to put it near food if it is lead based though. Anyone have any experience with this stuff?

Thank you!

[paulkjrobbins]

I think I figured the last one out. Its density is around 10,000 kg/m^3, it doesn't throw a spark, and is not magnetic. I think it is flexible lead sheeting. Oh well, maybe I'll find a use for it down the road.

[david s]

Yeah that looks like lead sheeting used for roofing.
Regarding the insulating firebricks, I think it is a mistake to use them around the oven mouth. Their low density means poor strength and they will take considerable bumps and abrasions in that location.If the gallery is cast rather than constructed of brick it can be strong and dense, but to reduce thermal mass can also be made thin. This is not possible using brick units and mortar.

[fox]

I have used insulating material to build the gallery but then had to line the sides with stainless steel, it is not an easy option and you need to design everything to allow for movement.
However it will make a considerable difference if you main objective is storing heat in the dome.

[paulkjrobbins]

Thank you for your replies! That helps so much as I am trying to get everything operational before it gets too cold. Considering your advice I think I am going to do something like the drawing below. The stainless steel mesh will cradle the fiberglass rope which I will put rigidizer on near the gap. This loop would avoid fraying of the mesh at the end and let the rope sit packed in the joint, but lose to move as things expand and contract

Other option: just have the mesh hang over the side, the purpose of it being to give me an 1/8" of better insulated space between the two arch bricks.

Another option: I may also just put one rigidized piece of rope in the bottom of the wedge (cemented to the wire mesh) and stuff the rest of it with FB with rigidizer on the bottom section of the FB.

I am pretty confident with my brick cross-section going forward. So I will probably just starting cutting those and then play around with the mesh, rope, FB, and rigidizer to see what looks and seems to work best. If you are reading this and anything jumps out at you please let me know before I do something stupid. I was thinking of using SS flashing to seperate the bricks and then I saw this SS mesh which is really cheap and seems like it would do the trick. I just have to cement the bottom edge of it as it tends to fray.

Thanks for your advice! This forum is awesome.

[mongota]

I used 1/2" ceramic fiber rope to fill the gap in my break. Two lengths of CF rope to be exact. I adhered it to the brick with a thin bead of high temp silicone. It was fast and easy. I cut the "L" cutout on my tile saw to get repetitive cuts, but used an angle grinder to shape the groove in the faces of the cutout to accept the rope. Also fast and easy.

[Gulf]

Be careful with, what they now call "L shaped brick". If you cut too much meat out of a brick it will be very brittle and prone to breakage. Either before or after they are in service. This is my early addition to heat breaks. Not the final placement. It was placed a little tighter before the actual placement but the bricks were cut the same as the pic. The wider reveal was chosen to accommodate the wider opening that the "flared" entries offered at the time without the intimidations

[paulkjrobbins]

I should have responded sooner, but thank you for the advice. My dome is now done, my outer arch form is up and I am cutting bricks and getting ready to lay them. I had a question about oven doors. In the posts for doors, I usually see them put together with rivets, SS bolts, or welded. Does anyone know about gluing one together with high-temp gasket cement? Seems like it would work in my head, but I have to think there is a reason why I don't see others doing it. Does anyone have any feedback on this point? Thank you for your help.

[fox]

A popular method to use when building doors would be to make a metal box and fill it with insulating material so what parts are you referring too when you say glueing them together?

[paulkjrobbins]

Hi Fox, thank you for checking in. I am referring to the actual stainless steel. Here is a drawing that gives some more detail to what I am imagining. I will probably stuff it with Fiber Board.

[fox]

Well I am not sure exactly what type of high temp gasket cement you are referring too but I cant say I have ever come across any type of cement that would stick a ss box together.
Perhaps a high temperature silicone might work, they are rated to around 250-280c but they dont really set hard like standard silicone and dont last long at the max temp rating
l have written before about using vermiculite board as a very easy and quick inner door but you will always need to handle it with care.

I would not use ceramic fibre board that has any exposed edges as you really do not want any loose fibres near you or your food!

[paulkjrobbins]

I was thinking of something like Rutlands Stove Gasket Cement . It bonds well to metal . It is commonly used on the forum to adhere fiberglass rope around the inner arch for a heat break. Some have used it to cement a cast-iron door to their gallery. I'm not sure how those doors worked out though. When it is fired it cures hard and is supposed to withstand up to 2000 degrees. Does anyone have any advice on using this to assemble a stainless steel door around fiberboard? I suppose if no one has done this before or can see a reason why it would be a bad idea I can try it out and be a ginny pig...

[fox]

Ok well that would be great if you can bond a metal box together that will stand up to the movement caused by heat expansion and cooling contraction.
Let us know how you get on….

[mongota]

I was thinking of something like Rutlands Stove Gasket Cement). It bonds well to metal . It is commonly used on the forum to adhere fiberglass rope around the inner arch for a heat break. Some have used it to cement a cast-iron door to their gallery. I'm not sure how those doors worked out though. When it is fired it cures hard and is supposed to withstand up to 2000 degrees. Does anyone have any advice on using this to assemble a stainless steel door around fiberboard? I suppose if no one has done this before or can see a reason why it would be a bad idea I can try it out and be a ginny pig...

You're right, it does state it can bond metal to metal, but it does state something about being used to make 'minor' metal to metal repairs.
I'd consider adding a few pop rivets. The rivets would provide holding power and the sealer would hold and seal.

[paulkjrobbins]

Hi Mongo and Fox, those are some really good points that you bring up. I don't have a rivet gun and don't want to have to deal with bending tabs. I think I will try to use the cement I mentioned to assemble it, but put some SS tubing on the inside maintaining the thickness with SS bolts going through them. Thank you for responding. That confirmation that I'm not missing some logic that is really obvious helps to go forward.