What causes ashes to cake-up?

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John_M

John_M

Minister of Fire
Dec 10, 2008
614
Central NY
At the end of a long fire I open the air all the way and rake most of the ashes to the front of the stove. I let them burn down and repeat the process until I have burned up most of the charcoal. Then I spread the remaining ashes to give a level platform to rekindle the fire.

While raking the ashes flat I notice large (2" to 5" dia., 1" thick) hard cakes of ashes near the front of the stove. They are seldom even warm and I could pick them up with my unprotected hands but I still wear gloves. These large cakes look like and have the same texture as broken fire brick. All my fire bricks are intact and sound so it is not my stove falling apart.

I have an OAK and these cakes are located just below where the outside air enters the firebox. I am not worried about these curious objects but am wondering how they are created.

Any suggestions?

John_M
 
I get em too, no clue why they form
 
The more that ash burns down, the finer it gets. In front of the air inlet there is lots of air to help combustion. That fine ash should compact pretty easily.

Matt
 
Could those be the infamous clinkers that pellet burners get?
 
These cowpies often form in places where there's a good layer of ash, where remaining combustible material causes the whole mass to cook together into crunchy patches. I have this happen sometimes in my ash bucket, where the ash will glow red hot down in the pile. It seems that the ash fuses itself into these crunchy masses after it cools.
 
I've heard it's from the weight of a full box compacting down the ash and the intense heat kind of fusing it together. It supposedly only happens in stoves without ash grates. No ash grate in my last two stoves and I get them too. Air comes in along the bottom back on mine and they can really interfere with a burn. Maybe that's the real reason why VC started adding ash doors. Mine pre-dates that. Took me a while to figure that one out since the last stove had air coming in through the front door and they merely took up space for wood but never affected the burn, actually seemed to help it to a point.
 
Battenkiller said:
I've heard it's from the weight of a full box compacting down the ash and the intense heat kind of fusing it together. It supposedly only happens in stoves without ash grates. No ash grate in my last two stoves and I get them too. Air comes in along the bottom back on mine and they can really interfere with a burn. Maybe that's the real reason why VC started adding ash doors. Mine pre-dates that. Took me a while to figure that one out since the last stove had air coming in through the front door and they merely took up space for wood but never affected the burn, actually seemed to help it to a point.
Click to expand...
Not sure what causes it, but I don't think an ash grate prevents it. My last stove, a VC cat, had an ash grate and I used to get these things all the time. Sometimes they were 6 inches across or more, and I could pick them up like a frozen pancake. They were always on the bottom of the ashes, right next to the grate surface. I could always tell when they were forming, as the ash would stop falling through the grate, even though the ash pan was nowhere near full. Have not seen this phenomenon this season, but I have no idea why the change. The operating differences are that I used to close down the old VC cat more than the new Oslo will go. I also used to rake and disturb the ashes a lot more than I do now, though I'd think that would prevent their formation, not encourage it. Dunno.
 
They form and clog up my grate too. Certainly there must be some potential commercial value to these things? If so, we must first come up with an enticing name for them other than Phoenix Poop. :)
 
I actually got them more with my stove with a grate so don't think that is it. I believe they are caused from weight and the intense heat at the front of the stove. Maybe we could call them stove diamonds!
 
I get them too and it seems like the longer I go without cleaning out the ashes the larger they become so I'm going with the theory that it's very fine ash material being compacted together from the intense heat at the bottom of the stove.
 
I never realized this is such a common occurrence. Perhaps there is a chemist among us who can tell us exactly how these are formed.

An impractical suggestion for commercial use of this product is to crush it and sell in 40# bags to be used as traction sand on driveway and in vehicles.

John_M :roll:
 
I too see these in my stove. I always welcomed them as it made it easier to clean out the ashes. Could it be a by product of Super Cedar or other similar firestarter?
Thomas
 
I'm not chemist, but I slept at a Holiday Inn last night.
But seriously, I know in my insert, the air comes in right at the bottom front there. That is where my bricks form.
I attribute it to since that is where the air comes in, that is the hottect area of the stove. And I believe the added air there, super heats the ash laying in front of the intake, and that heat and location of the ash causes those ashes to get hot enough to fuse together and form that brick, or cake or puck or whatever you wanna call it.
Thats my theory, but I am not chemist.
 
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