charred mass when sifting coals

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New Member
Oct 8, 2022
nova scotia
Sorry, no pictures, wish I'd thought of that but I'll do my best to describe.

This morning when I was raking the coals/ash, I dug a bit deeper than I have in the last week or two and scraped up this big mass of char. Hard to describe but it wasn't glowing like the rest of the coals, and it took a bit of effort to scrape up from the bottom. Like it had almost melted on there. I pushed it off to the side and once I had some good coals separated from ash I put it near the air intake where the coals had made a nice hot bed. It made a dull glow after a few minutes which extinguished almost as soon as I pulled it away.

Once I removed, my next fire burned much hotter and got to a secondary burn a lot quicker than it had the last few days. Can anyone tell me about this build up and what it might be? It didn't have any wood-like structure discernable. More like if you had some dirt, sand or plastic or something. It was right above the grate for the ashpan which I don' empty anymore as the stove runs better that way. I have had a few logs steam a bit the last week.

I have one of the older model hearthstone mansfield stoves, burning mixed hardwood that is not the driest but not the worst.
My guess is its "clinker" which is fused ash. No real BTU content as its already burned out. Different types of wood have different types of ash along with contaminants brought in along with the wood. The "ash" fuses at different temperatures. Odds are if you change your source of wood, your clinker will form differently. It can mess up air flow in the firebox, so best removed. It could help in early and late season as its going to reduce the volume of the firebox, so it may get hotter quick.
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Clinkers indeed. Be careful taking them out as sometimes they fuse to the firebrick. Don't want to damage the firebrick.
Takes a lot of heat to fuse ash. Usually clinkers are relegated to coal stoves and they will fuse to the fire brick. Especially if it hot enough to turn into a sort of glass. Usually won't come off at that point.
It depends a lot on the (mineral) composition of the wood. It's quite common to see clinkers in wood stoves too in my experience.
Thanks @peakbagger and others who replied. It has continued to happen, always around the doghouse or whatever you call the air flow box, so im guessing "clinkers" it is. Some of the wood had moss and lichen on the bark so there has been a lot of different stuff going in there I suppose. So long as its not an indication of something I'm doing wrong or that will harm things I'll just carry on, and aim for an earlier, bigger stockpile of better seasoned wood.
It's normal with some wood species. This is an annual question. Search on past threads in this forum on clinkers for more info.