what is the max thickness of ceramic to be fired?

[s6x]

I am making 40" tall sculptures and having issues with them collapsing once I hollow them out.   I split them in half horizontally, hollow them out, but when I put the top piece back on, they crumble.   I'm thinking I need to make the walls thicker, but how thick is too thick?  Any suggestions?  

[Bill Kielb]

some of my experience
Thickness will help, but you may be able to design around it depending on what is collapsing. Larger diameters if you will instead of tall and  slender can enhance the strength.  Horizontal shoulders collapse but gradual thickening inside can allow the force to distribute down into the sidewall clay on axis rather than a cantilever shoulder. So when practical select thickening of areas is definitely a thing for me.

[s6x]

thank you.  I'm making urn/vase shapes, so the top is just a cylinder basically, while the bottom is irregular shaped.  the top cylinder is also not a perfect fit after hollowing out, because as I'm turning it this way and that way its slowly changing shape... so when I put it back on, I have to get finicky with it, which adds addiontal stress on the bottom part.      What is the max thickness you can go?  I've been going half an inch thick, but if I could go 1" thick on the bottom, that would be helpful.  

[Kelly in AK]

My BFA professor was a sculptor, her work was around 4-5 feet tall and probably averaged an inch thick. She used an Imco sulpture clay, it was pretty groggy. Also fired very slowly. Another thing I've seen is people building reinforcing structure inside the sculpture, extra walls where support is needed. 

[s6x]

thank you

 

[baetheus]

You can use wooden dowels as supports and leave them in during the bisque (or even during glaze if you single fire). It's best to alter your firing schedule to climb more slowly through the organic burn out section (500F to 700F https://digitalfire.com/temperature/36), about 100-150F/hr if you can manage. Some sculptor who makes a lot of dogs uses this method. He also will block out the rough shape of the sculpture using entire 25lb blocks of clay, sculpt away until most of the work is done, blast the surface with fire, cut away a few lids and hollow out the sculpture, and then score slip his "lids" back on. I watched a video and he was incredibly quick using these techniques. Don't remember his name though, sorry.

Hope this helps!