outside the exterior of the chimney or outside of the firebox?
Pitch or tar is the by product of many fires. this stuff can be like gasoline when it accums too much. This could be a flag telling you do make some wise desisions quickly.
Rule of thumb, clean the flue and sweep the chimney after every two cords of burning. More often if certain species of wood are used.
That chimney burning log now advertised is a joke.
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