To apply cob to vertical surface, you work in stages. Bring the cob up slowly. Then after you get a few inches on, you use a sheetrock plastic wrap. If it can be wrapped around that is best. If not then
genteelly push it into your soft cob. Come back the next day and cob over your mesh. The mesh will help hold your cob up it also helps with cracking.
You are going to have cracking. Its not a problem you just need to use your finger and work new cob into the crack.
Another trick you might like is to add color to your cob. There are readily available dies for concrete you can use or natural dies in many colors.
Does coating a drum in cob give the drum a shorter lifespan since the heat cannot dissipate from it as fast?
I do not know the answer to that question, but your post brought it up in my mind.
Drums and cob are cheap so even if the drum metal did degrade faster it would be easy to swap out and likely worth the benefits of making the drum heat more slow and stable.
Hi Matt; That drum is seven years old now. Having cob on it did not hurt it at all.
Here is the same drum installed on my batchbox.
Not all who wander are lost... J.R.R. Tolkien
posted 2 weeks ago
Good question. I am using old pessure tanks so much thicker steel than barrels. I could not weld barrels and want to make my own variation. I want to be able to add verticle cob for several reaons. But mostly for making sure my sealed bell is extra sealed and also to control the initial heat. Not sure if this second part is correct but i think it might be a way to cover surface that give direct heat and therefore tune that heat for my own needs
Fraser, I didn't see a reply about the cardboard. While commonly used for airtight masonry heaters, using cardboard between the barrel and cob will result in a smoky mess and will take long time to burn out. What you need is a similar expansion joint between the two so that your cob doesn't crack. This doesn't need to be very thick, you can use refractory blanket that is really thin. I've found that the 1" blanket pulls apart fairly easily into quarter inch sheets. Try not to squish it too much when you apply cob. Build the cob slow, like 3" a day so that it doesn't pull away too much. Also, the thicker the cob, the less likely to crack. Make sure to use some long straw that will help hold it together.
Matt, I don't think that coating the barrel will result in degradation any faster than without. The mass from the cob picks up heat very well and should be able to quickly wick heat from the barrel to the mass to the air fairly quickly. Probably not as quickly as having the barrel completely exposed, but I think read that they are comparable.