# Castable refractory repair advice please



## Tango papa (Feb 3, 2017)

I have an old Meridian wood stove that came with my house. This is my first season burnugnwood and the stove was WETT certified as part of the purchase deal, but it was obvious that the inside refractory had been patched. I wasn't unduly concerned-- it is an old stove.  To picture this thing, there are documents posted elsewhere in the forum with illustrations, but basically the forebox is roughly spherical and completely lined with refractory cement.   In two spots, patches have started to fall away.  My hope is that the PO just didn't repair it properly.  You know, didn't remove unsound material, clean or pre- wet if necessary, etc.   This would be on line with some other repairs I have discovered since moving in.  Th earless are above the centreline, not quite at the top, which is a big hole for the flue pipe, but say half way up.  Any thoughts on how to effectively repair?  Back in the day, in the industry boiler industry, we always tried to have some kind of anchor but I can't see any way to really do that.  I am in Canada (for the sake of availability of brands and products here.  Home Hardware sell a refractory cement, good to 2200F, but will it adhere and stay?  Thanks in advance.


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## WoodyIsGoody (Feb 3, 2017)

Tango papa said:


> I have an old Meridian wood stove that came with my house. This is my first season burnugnwood and the stove was WETT certified as part of the purchase deal, but it was obvious that the inside refractory had been patched. I wasn't unduly concerned-- it is an old stove.  To picture this thing, there are documents posted elsewhere in the forum with illustrations, but basically the forebox is roughly spherical and completely lined with refractory cement.   In two spots, patches have started to fall away.  My hope is that the PO just didn't repair it properly.  You know, didn't remove unsound material, clean or pre- wet if necessary, etc.   This would be on line with some other repairs I have discovered since moving in.  Th earless are above the centreline, not quite at the top, which is a big hole for the flue pipe, but say half way up.  Any thoughts on how to effectively repair?  Back in the day, in the industry boiler industry, we always tried to have some kind of anchor but I can't see any way to really do that.  I am in Canada (for the sake of availability of brands and products here.  Home Hardware sell a refractory cement, good to 2200F, but will it adhere and stay?  Thanks in advance.



Can you tell why the ceramic firebox was lined with cement? If it's because the ceramic is cracked, I'm not sure any repair would be completely satisfactory. However, if it can be fixed, it would be worth doing because those fireboxes aren't available anymore (that I've heard of anyway).

Maybe someone with more high temp ceramic knowledge will chime in.


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## Tango papa (Feb 3, 2017)

I think I found what I am looking for.  Another thread on these stoves has maintenance instructions "Meiridian wood stove not heating home".   Now I need to find a product called CFC (Ceramic Fiber Composite).   It says you can use firebox cement, but only temporarily.  So far no luck.

Woody, it is a castable refractory cast fire chamber lined with the CFC.  That is just how they were made.  I gather that the previous owner used HT ce,met and it has now fallen off.


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## WoodyIsGoody (Feb 11, 2017)

Tango papa said:


> Woody, it is a castable refractory cast fire chamber lined with the CFC.  That is just how they were made.  I gather that the previous owner used HT ce,met and it has now fallen off.



That's interesting. I'll have to take a closer look at my in-laws Meridian firebox because I know it has been in very regular use for at least 25-30 years and has never needed any maintenance. Last time I looked closely it was still in excellent condition. I can't believe how white and bright the interior of the firebox stays even after thousands of fires! So the lining must be there to seal the clam shell design and insure an airtight combustion chamber?


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## Tango papa (Feb 11, 2017)

WoodyIsGoody said:


> That's interesting. I'll have to take a closer look at my in-laws Meridian firebox because I know it has been in very regular use for at least 25-30 years and has never needed any maintenance. Last time I looked closely it was still in excellent condition. I can't believe how white and bright the interior of the firebox stays even after thousands of fires! So the lining must be there to seal the clam shell design and insure an airtight combustion chamber?


Maybe, but the CFC material lines the whole interior, not just the seam area which I gather would be along the horizontal centreline.   I just think that the whole think is a big castable refractory sphere, maybe with a partial steel frame -- I saw something that looked like rusty steel in one or two of the bigger cavities -- and then they lined it with a higher temperature rated, and maybe more durable, material.  I think that is it. 

I sure wish mine had stood up as well as your in-laws' stove. I can't kick too much about the state of 30-year old refractory.  I have been curing it with small wood fires and with charcoal fires for the last two days. Right now we are starting a normal fire.  We will see. I used Imperial products.  Castable refractory, which did not stick easily on vertical or overhead surfaces.  I made it per the instructions and it was quite dry.  Then I touched it up with their grey firebrick cement where ther refractory did. It build up enough thickness.  That cement has already kind of curled and fallen off as it dried.  I didn't apply too thick, but maybe didn't fewer the underlying refractory enough.  

The spherical shape means that some longer logs are a tough fit.  I can see that if someone threw in too-long logs over time it could chip away at a hot surface. I don't know.  Do people see that with ordinary wood Stoves?  

I'm pretty much against disposing of s piece of kit that can be fixed, so even if I had to do an annual repair I wouldn't be too upset, but it has to hold up better than this. Once you get holes through the firebox wall, tramp air is getting sucked in and with the door wide open when lighting, smoke can seep out.  It may be too far gone, which is a true shame. The previous owner could have avoided this.  "a stitch in time saves nine".


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## WoodyIsGoody (Feb 11, 2017)

Tango papa said:


> Maybe, but the CFC material lines the whole interior, not just the seam area which I gather would be along the horizontal centreline.   I just think that the whole think is a big castable refractory sphere, maybe with a partial steel frame -- I saw something that looked like rusty steel in one or two of the bigger cavities -- and then they lined it with a higher temperature rated, and maybe more durable, material.  I think that is it.



Just FYI, the ceramic technology pioneered by the founder of Meridian is suitable for extreme heat, much hotter than steel can withstand, it doesn't need to be lined for that purpose. It could be for additional insulation AND sealing the seam.



> I sure wish mine had stood up as well as your in-laws' stove. I can't kick too much about the state of 30-year old refractory.  I have been curing it with small wood fires and with charcoal fires for the last two days. Right now we are starting a normal fire.  We will see.



Well, my father-in-law is 86 and has been cutting his own wood since a child. I've noticed he cuts all his wood to a very consistent length and splits it to very consistent sizes, no large splits. Always well seasoned. He never packs the firebox full, just opens the door and lightly tosses one or two (only if very cold outside) new splits in. As soon as the door is closed the new split is in almost instant secondary burn and the beautiful colors are reflected off the brilliant white firebox into the room. The beauty of the oval ceramic firebox is it's ability to generate very high internal temperatures without filling the firebox full or even half full. With all his splits properly sized, there is never any wear on the firebox. With well seasoned wood and the high internal temperatures the ash is pure powder, and almost non-existent. This stove is a remarkable space-age beauty although the gorgeous oval cast bronze? door evokes memories of an earlier maritime age, when things were built to outlast their creators.



> I used Imperial products.  Castable refractory, which did not stick easily on vertical or overhead surfaces.  I made it per the instructions and it was quite dry.  Then I touched it up with their grey firebrick cement where ther refractory did. It build up enough thickness.  That cement has already kind of curled and fallen off as it dried.  I didn't apply too thick, but maybe didn't fewer the underlying refractory enough.



I know quite a bit about the intricacies of cement, but I'm not familiar with refractory cement. What I do know leads me to think the failure of your repair likely had to do with how the product was used, not how the product was formulated (unless of course it is simply the wrong product for your application). My advice would be to consult an expert in the field of refractory cements (who are few and far between). It could be as simple as getting the moisture balance between the shell and the product correct. For this to work you need the product to form a chemical bond to the old surface. The old surface would need to be mechanically sound and ready to react with the product. Timing of mixing/apply the product is probably important as is the curing process. I'm sure it's part art/part science. You need more information. Or you could just get lucky. But I wouldn't count on luck because with complex processes there are many ways to fail. You need to know exactly what you are trying to do. Hence the need for more expertise.



> The spherical shape means that some longer logs are a tough fit.  I can see that if someone threw in too-long logs over time it could chip away at a hot surface. I don't know.  Do people see that with ordinary wood Stoves?



If by "ordinary wood stoves" you mean steel lined with firebrick, steel is more abrasion resistant. Firebricks do degrade with time and abuse but are probably at least as durable as refractory cement. I learned a long time ago that it is easier to use products and materials properly rather than abuse them/repair them. The inside of a Meridian firebox is not designed for cramming/wedging but will last many decades with intelligent usage.



> I'm pretty much against disposing of s piece of kit that can be fixed, so even if I had to do an annual repair I wouldn't be too upset, but it has to hold up better than this. Once you get holes through the firebox wall, tramp air is getting sucked in and with the door wide open when lighting, smoke can seep out.  It may be too far gone, which is a true shame. The previous owner could have avoided this.  "a stitch in time saves nine".



If it's repairable, and I suspect it is, you shouldn't need to repair it annually! Let us know what you learn.


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