Structural Slab for new WFO

[stonecutter]

Re: Structural Slab for new WFO

David mentioned why...ceramic is a better insulator, and would perform better next to the casting.

[mikku]

Re: Structural Slab for new WFO

It seems like your only issue is the insulation layer, so tearing the oven apart doesn't make sense.

If it was me, I would remove the perlcrete and wrap the oven with ceramic, cover that with a new layer of perlcrete, then apply the stucco.

Stonecutter, thank you as always!

You are giving me two different answers at the same time. I really do not want to wait for perlcrete to dry out AGAIN! That is the slowest part of the entire build!

What is the advantage of having the ceramic fiber closest to the oven?
I can understand you wanting it in the Normally preferred location, because of your perfectionist desire--but would there be any significant "measurable
difference" to what I suggest with just adding it to the exterior?

[mikku]

Re: Structural Slab for new WFO

Build a big oven then and you can spend lots of time cutting and splitting wood to keep you fit in old age.

This is the first time you have answered like Brickie, but he is always quick with his answers and likes to give a friendly dig once in a while--for you it is entirely out of character!

Please give me some specifics that back up "why" the ceramic fiber should be closest to the oven.

I totally disagree with the comment that it performs better in that location. To me that is completely incorrect. The performance of the insulation is the same no matter where in the assembly it is placed. The R value does not change! If it is listed in R! The physical characteristics do not change! So please inform me where I am wrong!

My replies are a little out of order because I had trouble with logging in last night--something that I was doing screwed things up so that I could not log in until tonite!

Yesterday--a little cabin fever because of a typhoon passing right over my location! Lost of wind, rain, storm damage, flooding, but everything is fine--I tied down things that were important--the rest---just let them fly away!

[stonecutter]

Re: Structural Slab for new WFO

Stonecutter, thank you as always!

You are giving me two different answers at the same time. I really do not want to wait for perlcrete to dry out AGAIN! That is the slowest part of the entire build!

I'm not sure I know what you mean by two answers...can you clarify?

You just have to decided what to do with suggestions from the forum. From my point of view, scraping the dome ( or selling it) isn't the way to go...from what you have described, it is well made. Taking off a layer of perlcrete should not be that big of a deal, since you have no finishes over it.

[stonecutter]

Re: Structural Slab for new WFO

What is the advantage of having the ceramic fiber closest to the oven?
--but would there be any significant "measurable
difference" to what I suggest with just adding it to the exterior?

Please give me some specifics that back up "why" the ceramic fiber should be closest to the oven..... The performance of the insulation is the same no matter where in the assembly it is placed.

"The performance of the insulation is the same no matter where in the assembly it is placed."

Yes, this is true. But the reasons I suggested putting the ceramic next to the dome are these....

1) Ideally, your best insulator should be on the dome. Perlcrete/Vcrete contains a material that conducts heat fairly well...Portland cement. Cermaic has a greater R value which will do a much better job at containing the heat that the mass is absorbing from your fire.

2) Wetness effects insulation. The outer layer of insulation will have a better chance of getting wet, than the inner layer. And, ceramic blankets or mineral wool absorb and hold water even better than Vcrete/perlcrete.

I believe you could tear off the old insulation, wrap with ceramic, and have a new P/V crete layer done in less than 8 hours.

[mikku]

Re: Structural Slab for new WFO

now here is a question for people like Brickie of Oz and David S or Stonecutter or a multiple of experts out there. The ones listed above I have the utmost of respect for their opinions--also Lawrence! Forgot to mention you -- my every day mentor!

Now I have to think about this topic. The oven is cured, but it does not have a final render coat or anything to make the oven waterproof or water resistant--if there is a difference.

My oven heats up very quickly, but it looses heat equally quickly! If you have been following my thread, I have at least 4" of pericrete surrounding my entire dome.

The pericrete has cracked, so what--the castable has not! But where the cracks are, there are hot spots. Hot enough to make you pull your hand away because it is too hot! Other locations are cool, like around the insulated chimney.

I am thinking about adding a layer or two of ceramic fiber to the outside of my render, then apply chicken wire and another coat of render!

Anyone see any problem with this idea? As long as the oven is insulated, the location of the insulation in the assembly is irrelevant--- RIGHT? Please, please correct me if I am wrong! If I add two layers of 1" thickness ceramic fiber to the outside of my --now half complete render coat, it should help retain heat longer--even though it is not the closest insulation in the total assembly!

My other alternative is to simply give up on the dome type oven style, make a box...out of light weight steel studding materials, cover the box with metal or concrete board or anything ---fill the cavity with vermiculite loose fill , install a sloped roof---make sure everything is water proof and call it good!

I'm tossing a lot of ideas around in my mind---I am really thinking about making a modular barrel type--like Brickie has but in castable-- make it larger to accommodate more bread making--and try some other options! This hole topic makes my mind go wild--anything is possible but I do not want a whole bunch of half finished ovens around my house! Maybe sell the one that I have and make a modular barrel--much larger!

My mind keeps wandering to different possibilities. How about some feedback on what to do with my current cast oven

This is a tough question--my present oven is not expensive by any means! it is labor intensive in the mold making area--but other things are really very cheap!

Brickie --what do you think? you had an oven that you tore back and rebuilt, if you were in my situation what would you do? Sell what you have and start a new design OR improve on the current design?

Davids- you have a very long time experience with castable ovens--make them every month........instead of a dome, what do you think of a barrel type like our friend in Canada made?

laurentius, I already have your thoughts but you can add to them as you wish!

I have a few days off--like "3" before starting a new project! I have a little time to think about alternatives. So please give me your honest
assessment!

That is it from this side of the planet--pray for peace during these crazy times in world politics!

Basically I was asking about the location of the ceramic blanket on the outside only--no changes but add to outside and chicken wire it and render coat. would that improve the performance of my oven considerably? It heats quickly, but it does not retain the heat as long as I would like it to!

Other option would be to sell it--making room for a more professional type of bread oven--that I have been thinking about making, like the guy in Canada making a huge oven all from brick. I am thinking of making a modular one, cross sections of a commercial oven from castable--maybe each section is only a foot deep but up to 4 feet wide. Using 3 modules--the oven would be 3 feet deep, same width--four modules 4' deep...then there would be a special mold for the transition to chimney and oven entry.

I did not intend to tear back anything... So when you said, mine was an insulation problem... that I agreed with; but when you said to tear back the perlcrete...I really wondered WHY, it ties into a lot of things right now. I thought that it would be counter productive.

so that is what prompted my answer..
I cannot visualize any difference between adding to outside or tearing back, placing the insulation against the dome, then re-applying perlicrete! Just the second way makes the project stretch out much longer because of the dryout of the perlcrete!

[mikku]

Re: Structural Slab for new WFO

"The performance of the insulation is the same no matter where in the assembly it is placed."

Yes, this is true. But the reasons I suggested putting the ceramic next to the dome are these....

1) Ideally, your best insulator should be on the dome. Perlcrete/Vcrete contains a material that conducts heat fairly well...Portland cement. Cermaic has a greater R value which will do a much better job at containing the heat that the mass is absorbing from your fire.

2) Wetness effects insulation. The outer layer of insulation will have a better chance of getting wet, than the inner layer. And, ceramic blankets or mineral wool absorb and hold water even better than Vcrete/perlcrete.

I believe you could tear off the old insulation, wrap with ceramic, and have a new P/V crete layer done in less than 8 hours.

I agree with that--except the P/V crete layer is done in the time quoted, but the drying will take weeks? no?

[stonecutter]

Re: Structural Slab for new WFO

I don't know about weeks, but it won't happen overnight..there are lots of variables.

You know, it kind if sounds like you want to build another oven anyway. So, then wrapping the oven with ceramic and then coating with stucco is seems like the most practical option. As is often the case, best practice is not always the best solution.

[mikku]

Re: Structural Slab for new WFO

I don't know about weeks, but it won't happen overnight..there are lots of variables.

You know, it kind if sounds like you want to build another oven anyway. So, then wrapping the oven with ceramic and then coating with stucco is seems like the most practical option. As is often the case, best practice is not always the best solution.

Well a new day and a fresh look at things!

This discussion began because of I was thinking about doing something. That is the problem, thinking about and not doing anything--but your input shamed me back to reality.. I have been trying to do a good job on the things that I do --all my life, but when it comes to things I do for myself, sometimes I lose patience and take short cuts.

Wanting to do something else is no excuse for taking short cuts. My original WFO was supposed to be economical--and I chose the economical way usually. Now that I see how my oven performs, I am looking for ways to improve on it. Taking a few steps backword might help with the performance overall. I have been wasting time since spring--at least since the first fire was built.. That is the WFO disease! Once it can burn and bake--no incentive to finish it.

Thanks again!

[david s]

Re: Structural Slab for new WFO

This is the first time you have answered like Brickie, but he is always quick with his answers and likes to give a friendly dig once in a while--for you it is entirely out of character!

Please give me some specifics that back up "why" the ceramic fiber should be closest to the oven.

I totally disagree with the comment that it performs better in that location. To me that is completely incorrect. The performance of the insulation is the same no matter where in the assembly it is placed. The R value does not change! If it is listed in R! The physical characteristics do not change! So please inform me where I am wrong!

My replies are a little out of order because I had trouble with logging in last night--something that I was doing screwed things up so that I could not log in until tonite!

Yesterday--a little cabin fever because of a typhoon passing right over my location! Lost of wind, rain, storm damage, flooding, but everything is fine--I tied down things that were important--the rest---just let them fly away!

Maybe my answer was "out of character" because the cracks in your vermicrete layer occurred because you did not take my advice about drying it.If you had followed my advice you would not be in the situation you are in presently.

One reason the blanket is better placed against the refractory is that you are preventing the heat entering the vermicrete layer.With the blanket on the outside you are storing more heat in the vermicrete layer. Another reason is that with vermicrete directly against the refractory, water that is stored in the vermicrete is far more easily turned to steam which,as you've found, can create problems.it is better and more efficient, but not mandatory, to place the better insulation closest to the heat source.

[mikku]

Re: Structural Slab for new WFO

Maybe my answer was "out of character" because the cracks in your vermicrete layer occurred because you did not take my advice about drying it.If you had followed my advice you would not be in the situation you are in presently.

One reason the blanket is better placed against the refractory is that you are preventing the heat entering the vermicrete layer.With the blanket on the outside you are storing more heat in the vermicrete layer. Another reason is that with vermicrete directly against the refractory, water that is stored in the vermicrete is far more easily turned to steam which,as you've found, can create problems.it is better and more efficient, but not mandatory, to place the better insulation closest to the heat source.

I see that the "comment like Brickie" is getting under your skin.. it should not, his answers are based on working with products for a lifetime, yours may be from studying the products and testing different things and manufacturing ovens.

But now you are talking out of both sides of your mouth at the same time!

I remember you telling me to take it slow with the application of the pericrete coats, and doing it in 1" layers. That part I did not take your advice--sometimes I use my own instinct... I do not think it created a problem except that it took much longer to dry.

I tried various ways of drying but in the long term, it was just time and firing of the oven.

You always had an opinion that ceramic fiber is a dangerous product, now you are hailing it as a superior product. What will you be advising tomorrow?

On most of the other things I have taken your advice over others and it has turned out fine.

As far as creating steam, no place or no time during my construction has steam created a problem or caused excessive cracking, Spaulding, explosions or anything. It is just a normal phase that water goes through in the drying process.

A lot of whoopla was made about the importance of slow curing for the refractory and I really wonder if that is all so important either. In commercial applications where refractory cements must be used on furnace repairs, they do not phase the temperatures up as everyone suggests. They have a kiln down for repairs and it is costing them money for the repairs and down time--when the repairs are completed, they want these machines on line as quickly as possible. And the temperatures that they are designed for are much higher than a WFO. Probably all the advice given on the forum is to be on the extremely safe side. I think the advice would be more important where quality of the build is concerned.

I mentioned cracking on my pericrete layer, but that is not the reason for considering installation of a ceramic blanket. I could add another 8" of pericrete and do the same thing for 1/10th the price. I just don't want to wait for the stuff to dry out like before. I will probably never use the stuff again because of the time lag--nothing else.

I wish you would "point fingers" when other people do not follow your advice.
This is also a first--as I have seen... out of character. I'm not Brickie, so you do not have to vent your frustrations because of some long standing feud or misunderstanding.

But thanks for all the information you have provided in the past.

It is like when people find themselves with little to do, they begin to infight among themselves. Usually I agree with your ideas... this time not so much!

[brickie in oz]

Re: Structural Slab for new WFO

No need to fight over me boys, there is enough to go around for everyone...........Ill make sure I bring some lube........

[david s]

Re: Structural Slab for new WFO

I see that the "comment like Brickie" is getting under your skin.. it should not, his answers are based on working with products for a lifetime, yours may be from studying the products and testing different things and manufacturing ovens.

But now you are talking out of both sides of your mouth at the same time!

I remember you telling me to take it slow with the application of the pericrete coats, and doing it in 1" layers. That part I did not take your advice--sometimes I use my own instinct... I do not think it created a problem except that it took much longer to dry.

I tried various ways of drying but in the long term, it was just time and firing of the oven.

You always had an opinion that ceramic fiber is a dangerous product, now you are hailing it as a superior product. What will you be advising tomorrow?

On most of the other things I have taken your advice over others and it has turned out fine.

As far as creating steam, no place or no time during my construction has steam created a problem or caused excessive cracking, Spaulding, explosions or anything. It is just a normal phase that water goes through in the drying process.

A lot of whoopla was made about the importance of slow curing for the refractory and I really wonder if that is all so important either. In commercial applications where refractory cements must be used on furnace repairs, they do not phase the temperatures up as everyone suggests. They have a kiln down for repairs and it is costing them money for the repairs and down time--when the repairs are completed, they want these machines on line as quickly as possible. And the temperatures that they are designed for are much higher than a WFO. Probably all the advice given on the forum is to be on the extremely safe side. I think the advice would be more important where quality of the build is concerned.

I mentioned cracking on my pericrete layer, but that is not the reason for considering installation of a ceramic blanket. I could add another 8" of pericrete and do the same thing for 1/10th the price. I just don't want to wait for the stuff to dry out like before. I will probably never use the stuff again because of the time lag--nothing else.

I wish you would "point fingers" when other people do not follow your advice.
This is also a first--as I have seen... out of character. I'm not Brickie, so you do not have to vent your frustrations because of some long standing feud or misunderstanding.

But thanks for all the information you have provided in the past.

It is like when people find themselves with little to do, they begin to infight among themselves. Usually I agree with your ideas... this time not so much!

Hi Mikku,

I think you misread the tone of my last post. I was certainly not acrimonious, I'm sorry if you read it that way, just trying to point out the facts. Your comment did not get under my skin. The reason I advised application of vermicete/perlcrete in 1" layers with a week of drying between each, is because that's the best way I've found to dry the stuff out. It's a bit like leaving a pile of sand in the sun. The top layer may dry, but underneath it will be wet for months. Driving the water out by fire, with a wet layer against the refractory can lead to rapid steam production which will swell and crack the vermicrete layer.This can occur well before there is any visible steam.
I have used ceramic blanket, but there are a number of reasons I prefer not to use it. One of those is safety, the stuff has produced tumours in rats, but to date there are no recorded human cases of cancers linked to CF. It is however banned for sale in Germany and we can't use it in schools here because children are considered more susceptible. It is still a superior quality insulator than either vermiculite or perlite. individuals can make up their own minds whether to use it or not.

[mikku]

Re: Structural Slab for new WFO

Maybe my answer was "out of character" because the cracks in your vermicrete layer occurred because you did not take my advice about drying it.If you had followed my advice you would not be in the situation you are in presently.

One reason the blanket is better placed against the refractory is that you are preventing the heat entering the vermicrete layer.With the blanket on the outside you are storing more heat in the vermicrete layer. Another reason is that with vermicrete directly against the refractory, water that is stored in the vermicrete is far more easily turned to steam which,as you've found, can create problems.it is better and more efficient, but not mandatory, to place the better insulation closest to the heat source.

MrChips said he likes this statement! What is to like about it?
I am not in any situation at the time--by build is like davids builds--same type of assembly... I see it lacking insulation and was looking for advice.

The answer I received seems like opinion rather than fact--IMHO should have prefaced everything said.

[mikku]

Re: Structural Slab for new WFO

Hi Mikku,

I think you misread the tone of my last post. I was certainly not acrimonious, I'm sorry if you read it that way, just trying to point out the facts. Your comment did not get under my skin. The reason I advised application of vermicete/perlcrete in 1" layers with a week of drying between each, is because that's the best way I've found to dry the stuff out. It's a bit like leaving a pile of sand in the sun. The top layer may dry, but underneath it will be wet for months. Driving the water out by fire, with a wet layer against the refractory can lead to rapid steam production which will swell and crack the vermicrete layer.This can occur well before there is any visible steam.
I have used ceramic blanket, but there are a number of reasons I prefer not to use it. One of those is safety, the stuff has produced tumours in rats, but to date there are no recorded human cases of cancers linked to CF. It is however banned for sale in Germany and we can't use it in schools here because children are considered more susceptible. It is still a superior quality insulator than either vermiculite or perlite. individuals can make up their own minds whether to use it or not.

I have heard those statements before as well as someone worrying about if the ceramic fiber was close to the dome and a crack would occur, the fiber might enter into the area where food is being prepared--another statement I heard that possibly ingestion is not a problem but inhalation is.

The scenario I stated keeps the fiber away from the dome itself--almost no chance of any fiber ever entering the burn chamber.

So with all those things to consider, why would you recommend using the stuff at all?

Big circular conversation really going nowhere..

But again, thank you for your response. I will certainly keep it in mind when I decide if I am going to make any changes at all!