refractory mortar

[briot]

I was uncertain about my abilities to construct the dome so I'm having an experienced mason help me. The local masonry supply told me to use pre-mixed refractory mortar for the dome and the mason agreed that it would be the best way to go. The dome is almost finished. Someone please tell me that we are using the right stuff? The joints on the inside of the oven are very small.

[dmun]

Re: refractory mortar

By pre-mixed, if you mean the wet stuff in tubs, it has been problematic in the past. It doesn't set up hard, and it isn't waterproof. If you maintain a meticulous curing schedule and your enclosure is really, really waterproof, you should be fine. If it's the pre-mixed dry stuff, like heat-stop 50, you're good to go.

More important is to be sure that your mason used the proper amounts and kinds of insulation. We've heard of more than one "expert" blow this crucial step off, as a waste of time and money.

[briot]

Re: refractory mortar

Yes, we used the wet stuff in tubs-it's called Greenpatch 421. The masonry supply here, which is the only one in town, told me that it was what they sold for pizza ovens. As far as customer satisfaction goes, I would rate them a zero. (Their initials are WG) I have even called a different business: Pumalite in Salem and they have been most helpful. I wish I had called them sooner, because the guys at WG are a bunch of idiots. I think I know more than they do, and I don't know much. I just keep asking for advice on the forum.
As soon as the dome is completed, my husband and I are doing the rest of the work. What do you mean by "meticulous curing schedule?" We will do the insulation and the enclosure. It will also have a roof. Is there anything more we need to do to keep it dry?
I'm suddenly having a lot of anxiety about this....

[dmun]

Re: refractory mortar

The roofed enclosure is the way to go. Pay attention to the flashing on the chimney, you don't want any leaks. By a meticulous curing schedule, I mean don't give in to the temptation to take shorcuts, and build up the fire bigger than it should be.

[cheech51288]

Re: refractory mortar

Word of Warning (about Greenpatch 421)-

I am a technician with a company that builds and repairs crematory equipment and we use Greenpatch 421 as a mortar in our cremators. Greenpatch 421 is a high-alumina style mortar designed to handle extreme temperatures in excess of 3200 degrees F. Likewise, the alumina content that exists in the mortar will be released as the mortar retains heat. The levels of alumina that are present in Greenpatch are very hazardous and are very carcinogenic. You are better off using Sairset Mortar (also made by Harbison-Walker, ANH refractories, and AP Green Refractories) which comes in the same 55 lb. bucket and costs a bit less. Although Sairset cannot withstand temperatures in excess of 2800 degrees F, it is safer with a lower alumina content.

[sacwoodpusher]

Re: refractory mortar

Word of Warning (about Greenpatch 421)-

I am a technician with a company that builds and repairs crematory equipment and we use Greenpatch 421 as a mortar in our cremators. Greenpatch 421 is a high-alumina style mortar designed to handle extreme temperatures in excess of 3200 degrees F. Likewise, the alumina content that exists in the mortar will be released as the mortar retains heat. The levels of alumina that are present in Greenpatch are very hazardous and are very carcinogenic. You are better off using Sairset Mortar (also made by Harbison-Walker, ANH refractories, and AP Green Refractories) which comes in the same 55 lb. bucket and costs a bit less. Although Sairset cannot withstand temperatures in excess of 2800 degrees F, it is safer with a lower alumina content.

I guess we are talking a matter of degree hear. According to the data sheets from the manufacturer......Greenpatch 421 and Sairset are kind of similar. Now, lets face facts here.....you should not breath dust from either of these, but if alumina is bad, then what difference is it the relative levels of alumina in the mix? Remember that we are not taking the temperatures of wood fired ovens anywhere near the level these materials are good for. All the MSDS sheets talk about is the danger of inhalation of CHRYSTALINE SILICA.

Greenpatch 421 Chemical Analysis: (Approximate)
(Calcined Basis)
Silica (SiO2) 39.4%
Alumina (Al2O3) 55.2
Titania (TiO2) 2.0
Iron Oxide (Fe2O3) 1.1
Lime (CaO) 0.2
Magnesia (MgO) 0.2
Alkalies (Na2O+K2O) 1.9

Sairset Chemical Analysis: (Approximate)
(Calcined Basis)
Silica (SiO2) 59.9%
Alumina (Al2O3) 33.3
Titania (TiO2) 2.3
Iron Oxide (Fe2O3) 1.4
Lime (CaO) 0.3
Magnesia (MgO) 0.2
Alkalies (Na2O+K2O) 2.6

[pizza_bob]

Re: refractory mortar

Low-duty firebrick itself has approximately 28% alumina. These bricks are fired at approximately 2000 degrees Fahrenheit during manufacturing. So do our oven temperatures of less than 1000 degrees Fahrenheit pose a risk? I wouldn't think so...

[C5dad]

Re: refractory mortar

And now for today's science lesson,

The vapor pressure of aluminum at 650 C is:

2.42E-06Pa@660.25?C ( or 3.5099e-10 psi @1200F)

The atmospheric pressure is: 101325 Pa or 14.7 psi

So, the volatilization of pure aluminum is very low.

However, we are not going into the oxidation of the aluminum at higher temps.

So we are all aware, aluminum ore (bauxite) is heated using electricity (resistance heating) to separate the aluminum from the ore concentrate. That is why most aluminum refineries in the US are in the northwest - cheap hydroelectric power.

[dmun]

Re: refractory mortar

That is why most aluminum refineries in the US are in the northwest - cheap hydroelectric power.

And why one of the first aluminum plants was in the shadow of Niagra Falls, and a new one is being built in Iceland.

Before the electric process was invented, aluminum was an incredibly rare metal. The emperor Napoleon once had a tableware set made from aluminum out of sheer ostentation.

Is it true that the aluminum oxide used in our firebricks is a by-product of the bauxite to aluminum process?

[Lburou]

Re: refractory mortar

And why one of the first aluminum plants was in the shadow of Niagra Falls, and a new one is being built in Iceland.

Before the electric process was invented, aluminum was an incredibly rare metal. The emperor Napoleon once had a tableware set made from aluminum out of sheer ostentation.

Is it true that the aluminum oxide used in our firebricks is a by-product of the bauxite to aluminum process?

10% of the earth's crust is aluminiun

[lwood]

Re: refractory mortar

Not sure I would want to use aluminum utensils. Have we come to some conclusion here?

[Tscarborough]

Re: refractory mortar

I use aluminum peels.

[pizza_bob]

Re: refractory mortar

I did away with my aluminum peel and brass bristled brush. I ordered and am expecting this pizza peel:

Amazon.com: Paderno World Cuisine 9-Inch Diameter Plain Stainless-Steel Pizza Peel, 59-Inch Long Handle: Kitchen & Dining

[C5dad]

Re: refractory mortar

Is it true that the aluminum oxide used in our firebricks is a by-product of the bauxite to aluminum process?

Unfortunately no. The byproduct is called red mud which has all sorts of cats and dogs. From what I understand, the mfgrs will do a controlled oxidation either when the aluminum is hot or via chemical.

If you want to see aluminum oxide being formed, get a really hot fire going and then toss an aluminum can in it. Do this in a fire pit as you need an excess of oxygen. You will see the can turn into ash - that is aluminum oxide.