Stainless steel wire-cloth/netting/mesh as a structural component

[MeLoN BaLLaR]

I am designing a light weight Neapolitan oven (think of it as a quick heating oven, i'm not baking bread for city-wide distribution)). I have all the materials for the dome and will begin laying up the blended FB mortar (FB mortar [darn fast delivery from Forno], stainless needles, fire-clay, pumice fines) for the domes hot-face over my mold.

Seems like the toughest part of the Neapolitan is the over-the-dome flue. I was thinking of cutting clay flue (cons, PITA to cut), but realized I could get stainless steel mesh/wire-cloth to form a very nice custom concrete flue over the dome. Pros: wide as the oven exhaust, low profile. I'm ok if it cracks, it just can't collapse. any thoughts or comments appreciated. I understand there are thermal differences between cement and stainless but if the needles work why not a stainless mesh?

Thanks,

MeLoN

[david s]

As long as the mesh is fine it should work. I think some Italian biscotti ovens used to use some fine bronze mesh in the centre of their castings, but delaminating at the mesh layer could be a problem. That is an advantage of random stainless needles.
if you are only using the mesh to form up against it is easier to use a double layer of much cheaper aluminium insect screen. Once the casting is dry it doesn't matter what happens to the mesh. You can then still use the random ss needles as the reinforcing.

[MeLoN BaLLaR]

Awesome thanks for replying David. I was thinking of fine gauge stainless steel chicken wire in the center of the pour (like rebar in a slab) with reinforcing needles (I bought 10 lbs) in the concrete mix.

[david s]

Hang on a minute. Have you enquired what is in the FB mortar brew? If you are also going to add pumice and fire clay then you will also need to add more of the cement used (probably calcium aluminate), in the FB mix to compensate for your additions of the other materials. For the flue gallery the temp is too hot to use normal cement. Higher up, for the chimney you may get away with using Portland cement where the temp is lower.

[MeLoN BaLLaR]

Hang on a minute. Have you enquired what is in the FB mortar brew? If you are also going to add pumice and fire clay then you will also need to add more of the cement used (probably calcium aluminate), in the FB mix to compensate for your additions of the other materials. For the flue gallery the temp is too hot to use normal cement. Higher up, for the chimney you may get away with using Portland cement where the temp is lower.

I just enquired. It's made onsite and appears to be a proprietary mixture. Assuming it's similar to RefMix:

AL203	about 30%
SiO2	about 50%
CaO	about 11%
K2O	about 3%
Ti02	about 1%
Fe2O3 + Feo	about 4%
Na2O	about 1%

So ~50% cement, 50% silica. I can add pumice at 1.5:1 to get a 1:1:3 cement:silica: pumice mixture. Then 5% stainless needles by weight. No fireclay needed (I'll use it to place the firebrick floor). I will use the FB mortar from the hotface to the ceramic insulation, including the flue gallery (cool term, thanks for teaching me that) and the chimney (if I don't go stainless). After the ceramic insulation, I will use portland and 3/16's(5mm) pumice stone in 1:4 ratio.


This is actually easier overall. I don't have to make pumice fines until maybe the final insulation layer post ceramic insulation. Portland:5mm pumice: pumice fines 1:2:2.

thanks!

[david s]

,

I just enquired. It's made onsite and appears to be a proprietary mixture. Assuming it's similar to RefMix:

AL203	about 30%
SiO2	about 50%
CaO	about 11%
K2O	about 3%
Ti02	about 1%
Fe2O3 + Feo	about 4%
Na2O	about 1%

So ~50% cement, 50% silica. I can add pumice at 1.5:1 to get a 1:1:3 cement:silica: pumice mixture. Then 5% stainless needles by weight. No fireclay needed (I'll use it to place the firebrick floor). I will use the FB mortar from the hotface to the ceramic insulation, including the flue gallery (cool term, thanks for teaching me that) and the chimney (if I don't go stainless). After the ceramic insulation, I will use portland and 3/16's(5mm) pumice stone in 1:4 ratio.

The figures you quote in the table relate to the composition of the total mix. They do not tell you the proportion or composition of the cement content. For example sand is composed of both silica and alumina in varying proportions as are other aggregates. Presuming the FB mix is the same as the one you quote is unwise. Find out if the mix contains calcium aluminate cement or calcium silicate cement, then you can boost the mix with extra cement to compensate for the addition of the pumice.

This is actually easier overall. I don't have to make pumice fines until maybe the final insulation layer post ceramic insulation. Portland:5mm pumice: pumice fines 1:2:2.

thanks!

The table you have provided relates to a different product. Assuming the FB mix is the same is unwise. The chemical composition of the mix quoted relates to the total, you can't assume that 50% of it is cement. For example sand usually contains both silica and alumina in varying proportions depending on its source, neither of which have been calcined. You should find out whether the mix uses calcium aluminate cement or calcium silicate cement then boost your mix with the extra cement to compensate for the addition of the pumice.
Usually mortars are designed to be weaker than whatever they're joining so using it as a castable will probably result in too weak a mix. A proprietary castable designed for the purpose will usually have a higher cement content.
Making up your own castable mix is not easy as a decent balance of workability, setting time, strength, thermal expansion and refractory qualities is required. Good luck.

[MeLoN BaLLaR]

,

The table you have provided relates to a different product. Assuming the FB mix is the same is unwise. The chemical composition of the mix quoted relates to the total, you can't assume that 50% of it is cement. For example sand usually contains both silica and alumina in varying proportions depending on its source, neither of which have been calcined. You should find out whether the mix uses calcium aluminate cement or calcium silicate cement then boost your mix with the extra cement to compensate for the addition of the pumice.
Usually mortars are designed to be weaker than whatever they're joining so using it as a castable will probably result in too weak a mix. A proprietary castable designed for the purpose will usually have a higher cement content.
Making up your own castable mix is not easy as a decent balance of workability, setting time, strength, thermal expansion and refractory qualities is required. Good luck.

I am going to make some test batches. I will report back. Otherwise, I'm sort of stuck with Rutland. thanks for helping me. really appreciate it

[MeLoN BaLLaR]

,

The table you have provided relates to a different product. Assuming the FB mix is the same is unwise. The chemical composition of the mix quoted relates to the total, you can't assume that 50% of it is cement. For example sand usually contains both silica and alumina in varying proportions depending on its source, neither of which have been calcined. You should find out whether the mix uses calcium aluminate cement or calcium silicate cement then boost your mix with the extra cement to compensate for the addition of the pumice.
Usually mortars are designed to be weaker than whatever they're joining so using it as a castable will probably result in too weak a mix. A proprietary castable designed for the purpose will usually have a higher cement content.
Making up your own castable mix is not easy as a decent balance of workability, setting time, strength, thermal expansion and refractory qualities is required. Good luck.

There was a spec sheet IN the bag of FB mortar. 125psi no additions. I can get 400psi with Portland and 5 parts pumice. I'm going to go back to my original plan and use Portland for the exterior dome, unmold, flip the dome over, trowel in the FB mortar with stainless needles for the hotface.

Thanks for your continual help. I could have really wasted a lot of time.

[david s]

There was a spec sheet IN the bag of FB mortar. 125psi no additions. I can get 400psi with Portland and 5 parts pumice. I'm going to go back to my original plan and use Portland for the exterior dome, unmold, flip the dome over, trowel in the FB mortar with stainless needles for the hotface.

Thanks for your continual help. I could have really wasted a lot of time.

Don't forget to insulate it. I hope you have access to a crane. Good luck.

[MeLoN BaLLaR]

Don't forget to insulate it. I hope you have access to a crane. Good luck.

You think? a cubic foot of concrete weighs 150lbs. I've got less than 1/2 a cubic foot in hot face (75lbs) and ~1.0-1.5 cubic feet of a pumice portland @ 100lbs per cubic foot (or less). so 200lbs for the dome, not including the door way/flue arch.

I'm buying the FB ceramic blanket (1" wrapped twice) and the 2" FB ceramic board. I was going to chicken wire up the insulation, set it on the ceramic board, add the spilt brick floor (on sand and fireclay), fire it slowly over a few weeks (see if this design is workable). I'm estimating its 400lbs in this test configuration. 6 man carry. Then set it in it's final resting place on 2" of pumice concrete. Finish the flue gallery, chimney, exterior, etc.

[david s]

Ah. ok. You didn't say what size the oven was to be. Must be pretty small. Should be manageable then.

[david s]

There is one thing that your FB mortar does probably not contain that proprietary castables do and that is the fine fibres that burn away at low temperature to reduce steam spalling. You can add these to your mix and they are available from concrete technology suppliers. They are polypropylene fibres and are thinner than human hair. The difficulty getting them to disperse in the mix requires mixing about double the normal time which is a bit more effort. Some folk have used chopped up polypropylene rope. I'm not sure this would work as their fibres are much thicker producing a smaller network. You should also test the temperature at which they melt, maybe not all polypropylene has the same melting point. The dedicated fibres melt at 160 C, if its much further north of this then the steam will do its damage before the fibres have melted or burnt out, making them pretty much useless.

[admin]

I have been following this thread and felt the need to clarify something.

Forno Bravo's FB mortar is not designed for refraction and thermal mass. It is used primarily for mortaring the oven dome joints on the top of the dome, below the insulation. It is high temperature refractory, but not a proprietary formula designed for refraction and properties which improve thermal performance of the oven.

Our proprietary formula is used on the oven dome itself which is similar to the formula table above, but different. We agree 100% about using poly fibers.

Fire brick formula is comparable to what is sold by Harbison Walker Refractories, but we use a higher alumina silica content, about 38% instead of 32%, for thermal shock inhibitor to limit spalling, pitting and cracking over time.

A good article thread to read can be found here on the main site.

https://www.fornobravo.com/pompeii-o...e-of-contents/

Thanks for the dialogue.

[david s]

I have been following this thread and felt the need to clarify something.

Forno Bravo's FB mortar is not designed for refraction and thermal mass. It is used primarily for mortaring the oven dome joints on the top of the dome, below the insulation. It is high temperature refractory, but not a proprietary formula designed for refraction and properties which improve thermal performance of the oven.

Our proprietary formula is used on the oven dome itself which is similar to the formula table above, but different. We agree 100% about using poly fibers.

Fire brick formula is comparable to what is sold by Harbison Walker Refractories, but we use a higher alumina silica content, about 38% instead of 32%, for thermal shock inhibitor to limit spalling, pitting and cracking over time.




A good article thread to read can be found here on the main site.

https://www.fornobravo.com/pompeii-o...e-of-contents/

Thanks for the dialogue.

Thanks for that clarification Tim. So what kind of cement is contained in the FB mortar? Is it calcium aluminate, calcium silicate, lime or something else?

Regarding the polypropylene fibres, I did a test today, melting
A:fibres contained in my proprietary castable mix,
B: dedicated fine polypropylene fibres for the concrete industry and
C: cut strands of polypropylene rope
.
The results were that fibres A and B melted at 160C as expected, but it took up to 220 C for C fibres to melt.
This could be because the C fibres are so much thicker (like around 10 x). While the rope fibres were more like really thick beard hair fibres A and B are much finer than human hair. The properties of polypropylene may also vary considerably depending on design.
From my experience in pottery steam spalling usually occurs somewhere between 200 - 300 C although water boils at 100 C. Presumably steam pressure at the higher temps is far greater.
Conclusion: I wouldn't be relying on poly rope to help eliminate water because of the less dense network it would leave behind (like having only main highways without any backroads and streets) and the higher temperature required for it to burn out.

[MeLoN BaLLaR]

I have been following this thread and felt the need to clarify something.

Forno Bravo's FB mortar is not designed for refraction and thermal mass. It is used primarily for mortaring the oven dome joints on the top of the dome, below the insulation. It is high temperature refractory, but not a proprietary formula designed for refraction and properties which improve thermal performance of the oven.

Our proprietary formula is used on the oven dome itself which is similar to the formula table above, but different. We agree 100% about using poly fibers.

Fire brick formula is comparable to what is sold by Harbison Walker Refractories, but we use a higher alumina silica content, about 38% instead of 32%, for thermal shock inhibitor to limit spalling, pitting and cracking over time.

A good article thread to read can be found here on the main site.

https://www.fornobravo.com/pompeii-o...e-of-contents/

Thanks for the dialogue.

Thanks for the reply Tim. I bought 25lbs of Rutland for the hotface