Chimney – Possible Weight Emergency

[stevef22]

Hello, I poured about 780 lbs of concrete mixed with perlite to fill the wooden form. Inside the chimney form is a double wall galvanized chimney pipes. They are 8 feet tall. Inner chimney is 8” outer is 11.5”


Im concerned about weight on existing arch. Possible arch blow out is a big issue on my mind.

In hindsight I should have build the chimney out of hardy board and just added stucco over it. But Im here now.


My welder freind came over, we are planning on welding some 1/4 “ flat strap steel to the outside of chimney and then down the sides to the main base. Then concrete anchor the flat strap steel against the base the base. This will add support to the arch if it decides to blow out. The steel will contain the arch and now alow it to blow out.

Please see pictures with yellow highlight to show the welding idea.

My question to you is…

1. Should I dismantle the chimney? Cut away the cement etc.
2. Should I go ahead and weld some flat bar to the chimney and add support for the arch and arch base.
   
   
   Google drive link with more pictures.
   
   https://drive.google.com/drive/folders/1p4K68BkjlGE1mAxvPac0e-BxViRnFP_i?usp=sharing
   
   
   What would you do?
   
   
   Thank you
   
   
   
   

[david s]

Hi Steve.

The common solution is to use a stainless pipe which is light and won't corrode. Unfortunately your system employs a lot of weight and the galvanised pipe will probably rust out pretty quickly down the bottom where it will be hottest. The risk of the weight on the arch creating failure is reduced somewhat by the outer render supporting it at the sides. The failure of the galvanised pipe also may not matter because of the material that surrounds it. I would be inclined to either do nothing and see how it all goes, or remove the whole chimney and replace it with a thin stainless pipe. But be careful because most building codes require a double thickness stainless flue if penetrating a roof.

Regards,
Dave

[stevef22]

Hi Steve.

The common solution is to use a stainless pipe which is light and won't corrode. Unfortunately your system employs a lot of weight and the galvanised pipe will probably rust out pretty quickly down the bottom where it will be hottest. The risk of the weight on the arch creating failure is reduced somewhat by the outer render supporting it at the sides. The failure of the galvanised pipe also may not matter because of the material that surrounds it. I would be inclined to either do nothing and see how it all goes, or remove the whole chimney and replace it with a thin stainless pipe. But be careful because most building codes require a double thickness stainless flue if penetrating a roof.

Regards,
Dave

Thank you for the input! Much appreciated. I think for now we will just see how it goes... I will update this thread with my solution.

Cant promise its the best or correct solution.


Thank you!

[david s]

Yeah I think that's what I'd be doing too. The thought of undoing all that work for a solution that may not be required, is daunting, however I'm sure you'll take that into consideration for the next oven you build.
I'm all in favour of pushing the envelope and using trial and error to see what you can get away with, I certainly have. After all "rules are made to be broken".
Many solutions might be on the boundary of being ok or failure and it's only with experience that we find out if it works or not.