Sorry if this looks strange I'm doing on a crappy old andoid phone.
1) is it critical to do the second burn if you are adding to cob or Adobe
2) is it critical to do a second burn to create a breathiable "lime pkaster" from Ash.
I live in the very dry desert and don't have the means to do a second burn safely, even in winter
3( Can you do a second burn without making it into balls
Thanks for reviving this post! I have lots of Ash and my husband thinks in hoarding. I need to have a plan or it's going into the compost.
quote=Spencer Miles]The reason that Prim re-fired was to calcine the calcium in the ash... no pun (not really)
The decanting that he did floated away the LOI (loss on ignition - unburned charcoal).
His video is a little misleading - and this thread has some issues related to it.
Generally (GENERALLY!!) Wood Ash is primarily Calcium and Silicon (with metals - primarily Aluminum) and that is mostly (MOSTLY!!!) the same as Portland Cement.
Wood Ash in general is chemically identical (IN GENERAL!) to Ordinary Portland Cement.
Why doesn't your fire-pit turn to a cement block? Metastable Crystalline Structure!!
When OPC clinker comes out of the kiln, it has to be rapidly cooled, or the crystals in it grow into more stable forms and combine with humidity to create expensive, sterile, and caustic sand/gravel/dust - ash.
Wood fires cool slowly, so the ash becomes hydrated and stabilized.
Prim's video shows first the fire to make the ash - this is incidental to the process, the first fire doesn't mean much and may as well have been a cooking fire.
The second fire is the key. Before the second fire, he "purifies" the ash by decanting the LOI - this is good. In the second fire, the ash balls that he made glow - this is calcination that drives the CO2 out of what is essentially limestone in the ash (that is produced by the slow cooling - limestone is already carbonated via a chain reaction from hydration to carbonation)
Something missing in his video is that the inner part of the ash-ball is insulated from the air/humidity, so it cools slower than the skin of the ball, and is not converted to a non-reactive (useless) form of Calcium.
Then he adds fired clay dust. Clay is alumino-silicate goodies, and the firing process creates a meta-crystal. Vis Metakaolin as opposed to kaolin. Metastable clay is a Pozzolan... much argument and many Romans....
The most important part here is the RAPID cooling of the ash (again, after it has been made - the first fire is not part of the cement process, all it does is make ash...) Prim did it via a ball of ash, and dropping it in water.
The use of naturally cooled wood-ash in concrete or plaster or mortar adds a little bit of reactive lime (calcium) to the mix - but it is mostly a super-fine filler and to a lesser extent an added Pozzolan (again, Concrete Chem is a field of many dangers!!)
Just mixing Wood Ash into Portland is certainly good - but to replace Portland all together with wood ash requires that the ash be heated to red-glow, then cooled as rapidly as possible. This actually makes it INTO Portland Cement, just with a dirty and uncontrolled recipe.
My plan (and why I'm back here again after a few months of research, experimentation, failure, and re-thought) is to make a diy rotary kiln. Seriously. Get the ash super-hot, then blow huge amounts of air over it without creating a dust-cloud of doom. My mountain has a severe lack of limestone, and my wallet has a severe lack of portland cement