Cracks in sand/clay dome

[soren]

Should I worry about these cracks? They appeared after I went “full heat” on my home built oven the first time.

- Dome is 80 cm diameter sand & clay. 7cm thick

- I plan to insulate with ceramic blanket and perhaps finish with “vermicrete”

[oblertone]

The vast majority of WFO's have cracks; you have the opportunity to do something about yours before adding your chosen insulation. A wet slurry of your dome mix certainly won't do any harm to your dome, but carefully staged drying fires would help.

[soren]

Sounds like a good idea.

It got me to thinking about perhaps actually removing some material to make the lower part of the crack wide enough (5-7 mm) so that I can reliably fill it with more dome mix. The thinking is that it would create a better bond between the cracked surfaces.

[downunderdave]

Jun 16, 2021 7:40:08 GMT oblertone said:

The vast majority of WFO's have cracks; you have the opportunity to do something about yours before adding your chosen insulation. A wet slurry of your dome mix certainly won't do any harm to your dome, but carefully staged drying fires would help.

filling cracks in a dried clay mix is usually unsuccessful. Especially if a thin wet mix is used. Because extra water in the mix increases the volume, when it dries it simply shrinks away from the crack. Your best chance is to sieve the coarse sand out of your mix. Wet the crack a number of times before applying the mix in a mix no thinner than a peanut butter consistency, using 50/50 water and vinegar to get to the peanut butter state. forcing it hard into the cracks. The vinegar assists in bonding.